JPH0715075A - Short pulse laser light source - Google Patents

Abstract

PURPOSE:To obtain a short pulse light having variable wavelength by feeding the light, emitted from a nonlinear optical medium upon reentrance during reverse optical parametric process, back to a laser medium thereby shortening the duration of pulse. CONSTITUTION:A beam (wavelength lambdaOSC) emitted from a laser medium 1 passes through a unidirectional unit 5 and reflected on a mirror M1. The beam is then passed through lenses L1, L2 in order to increase the power density thereof before the beam impinges on a nonlinear optical crystal X1. Consequently, two beams having wavelengths lambdaS1, lambdaS2 are generated in the crystal X1 through a parametric process. The original wavelength lambdaOSC is recovered at a second nonlinear optical crystal X2 through an optical parametric process reverse to that of the first crystal X1. In other words, the light having wavelength lambdaOSC emitted from the crystal X2 passes through lenses L3, L4 where the original beam diameter is recovered and then the light is reflected on a mirror MS back to the laser medium. Since the combination acts as a mirror which reflects the light more as the incident intensity thereof increases, i.e., a saturable absorber, a short pulse light can be generated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a short pulse laser light source, and more particularly to a mode-locking short pulse laser light source.

[0002]

2. Description of the Related Art As a short pulse laser light source, a short pulse laser light source using a passive mode-locking method or an active mode-locking method is known.

In a passive mode-locked laser light source, a dye solution is placed as a saturable absorber in a laser resonator,
When a light pulse passes through this dye solution, loss or phase modulation is automatically generated according to the pulse waveform, and a short pulse light can be obtained for practical use. On the other hand, an active mode-locked laser light source that uses a light modulation element and forcibly synchronizes the phase by adding a signal that matches the traveling cycle of light has been put to practical use. There is.

Further, as another short pulse laser light source, there is one which can obtain short pulse light of two kinds of wavelengths disclosed in Japanese Patent Laid-Open No. 1-147881. This is shown in FIG.
The laser medium 1, the nonlinear optical medium X, and the mirror M ₃ are arranged in the laser resonator including the mirrors M ₁ and M ₂ .

According to this structure, by pumping the laser medium 1, laser resonant light having a frequency (fundamental frequency) determined by the laser medium is generated, and when this laser resonant light is incident on the nonlinear optical medium X, In the nonlinear optical medium X, radiated light (second harmonic wave; SHG) having a frequency twice the fundamental frequency can be obtained. Here, the mirror M ₁ totally reflects light of the fundamental frequency, and the mirror M ₂ is SHG 1
00% and 25% of the fundamental frequency are reflected, and the mirror M ₃ is S
Selectively reflect HG. Mirror M ₂ is 25% of fundamental frequency
Is reflected, a loss occurs according to the pulse waveform, and short pulse light is obtained.

[0006]

The above-mentioned passive mode-locking method uses a dye solution, but there are problems that the kinds of dyes are limited and that the life is short and stable output cannot be obtained for a long time. . On the other hand, the active mode locking method has a problem that the structure is complicated and it is difficult to perform the mode locking of the pulse oscillation. Further, neither of them can selectively generate and take out short-pulse light having a desired wavelength over a wide range.

Further, the structure of the Japanese Patent Laid-Open No. 1-147881 is simple, but as described above, the pulse is shortened by the mirror whose reflectance is fixed to uniformly reflect light of all intensities. Therefore, there is a problem that it is not possible to obtain a short pulse light having a sufficiently narrow pulse time width.
Furthermore, by setting a non-linear optical medium X called an SHG crystal in the laser resonator, it is possible to obtain short pulsed light having a frequency twice the fundamental frequency in addition to short pulsed light having the fundamental frequency. Was fixed at twice the fundamental frequency. That is, there is a problem that the wavelength of the short pulse light cannot be selected.

The present invention has been made in order to overcome the above-mentioned problems. A short pulse laser light source capable of performing mode locking by utilizing an optical parametric process and outputting a short pulse light having a sufficiently narrow pulse time width. And a short pulse laser light source capable of simultaneously outputting multiple wavelengths and selectively generating and extracting short pulse light of a desired wavelength over a wide range.

[0009]

A first short pulse laser light source according to the present invention is a laser medium, a laser resonator having the laser medium therein, and a nonlinear optical device provided inside the laser resonator. An extraction means for selectively extracting the generated light in the optical parametric process generated when the generated light from the laser medium is incident on the nonlinear optical medium and re-incident on the nonlinear optical medium; and It is characterized in that the light generated in the optical parametric reverse process generated in the nonlinear optical medium by the re-incident by the means is fed back to the laser medium. Here, this short pulse laser light source may be characterized in that an optical means for correcting the group velocity dispersion of the generated light in the optical parametric process is arranged on the optical path between the nonlinear optical medium and the extracting means.

A second short pulse laser light source according to the present invention is a laser medium, a laser resonator having the laser medium therein, a nonlinear optical medium provided inside the laser resonator, and a laser. Extraction means for selectively extracting the generated light in the optical parametric process that occurs when the generated light from the medium is incident on the nonlinear optical medium and re-entering the nonlinear optical medium, and the generated light in the optical parametric process. And a selective emission means for selecting and emitting from the resonator those not involved in the optical parametric reverse process occurring in the nonlinear optical medium by re-incident by the extraction means,
It is characterized in that the light generated in the optical parametric reverse process generated in the nonlinear optical medium by re-incident is fed back to the laser medium. Here, this short pulse laser light source may be characterized by having a rotating means for rotating the nonlinear optical medium or a temperature adjusting means for adjusting the temperature of the nonlinear optical medium. Further, it may be characterized in that it has one or more optical means for correcting the group velocity dispersion of the generated light in the optical parametric process.

A third short pulse laser light source according to the present invention is a laser medium, a laser resonator having the laser medium therein, and a laser medium provided inside the laser resonator. A first non-linear optical medium that causes an optical parametric process by the incidence of light, an extracting unit that selectively extracts the generated light in the optical parametric process, and an incidence of the generated light in the optical parametric process extracted by the extracting unit. The second non-linear optical medium that causes the optical parametric reverse process is provided, and the generated light in the optical parametric reverse process is fed back to the laser medium. Here, in this short pulse laser light source, an optical means for correcting the group velocity dispersion of the generated light in the optical parametric process is arranged on the optical path between the first nonlinear optical medium and the second nonlinear optical medium. It may be characterized. Further, it may be characterized in that an optical path length adjusting means for adjusting an optical path length in the resonator is provided so that generated lights from the laser mediums traveling in opposite directions along the optical path collide in the nonlinear optical medium. .

A fourth short pulse laser light source according to the present invention is a laser medium, a laser resonator having the laser medium therein, and a laser medium provided inside the laser resonator. A first non-linear optical medium that causes an optical parametric process by the incidence of light, an extracting unit that selectively extracts the generated light in the optical parametric process, and an incidence of the generated light in the optical parametric process extracted by the extracting unit. And a second nonlinear optical medium that causes an optical parametric inverse process by the first and an optical parametric process that is generated by the first nonlinear optical medium.
The non-linear optical medium of (1) is provided with selective emission means for selecting and emitting from the resonator those not involved in the optical parametric inverse process, and the generated light in the optical parametric inverse process is fed back to the laser medium. Characterize. Here, this short pulse laser light source may have a rotating means for rotating the first nonlinear optical medium and a rotating means for rotating the second nonlinear optical medium, and operate both of them in conjunction. . Further, it may be characterized in that it has a temperature adjusting means for adjusting the temperatures of the first and second nonlinear optical media. Further, it may be characterized in that it has an optical path length adjusting means for adjusting the optical path length in the resonator, and that the generated lights from the laser mediums traveling in opposite directions along the optical path collide in the nonlinear optical medium. . Further, it may be characterized by having one or more optical means for correcting the group velocity dispersion of the generated light in the optical parametric process.

[0013]

In the first short pulse laser light source according to the present invention,
When the light generated from the laser medium enters the nonlinear optical medium and an optical parametric process occurs, the ratio of the intensity of light generated in this optical parametric process to the incident light intensity becomes nonlinear, and the intensity ratio is emphasized by this optical parametric process. The generated light thus extracted is extracted by the extraction means and is incident on the nonlinear optical medium again. Then, since the intensity ratio is emphasized again by the optical parametric reverse process, the combination of the extraction means (for example, the mirror) and the nonlinear optical medium acts as a mirror in which the reflectance becomes higher as the light intensity becomes higher. Therefore, it becomes possible to generate short pulsed light, and from the extraction means,
Light generated from the laser medium that does not participate in the optical parametric process is emitted as short pulse light. Also,
The light emitted from the nonlinear optical medium after re-incident returns to the laser medium and causes stimulated emission.

The wavelength dispersion of the refractive index of each optical element causes the group velocity dispersion of the generated light in the optical parametric process.
The optical means for correcting group velocity dispersion arranged on the optical path between the nonlinear optical medium and the extracting means corrects this group velocity dispersion and then re-enters the generated light in the optical parametric process into the nonlinear optical medium. Let

In the second short pulse laser light source according to the present invention, in addition to the same operation as the first short pulse laser light source, the selective emitting means is the generated light in the optical parametric process and is the optical parametric inverse. Those which do not participate in the process are selected and emitted as short pulse light. The light generated in the reverse process returns to the laser medium and causes stimulated emission.

A third short-pulse laser light source according to the present invention is the same as the above-mentioned first short-pulse laser light source except that a nonlinear optical medium that causes an optical parametric process and a nonlinear optical medium that causes an inverse process are separated. is there. When the light generated from the laser medium is incident on one of the nonlinear optical media and an optical parametric process occurs, the ratio of the intensity of the light generated in the optical parametric process and the intensity of the incident light becomes non-linear, and the intensity ratio by this optical parametric process. The generated light in which is emphasized is extracted by the extraction means and is incident on the other nonlinear optical medium. Then, the intensity ratio is emphasized again by the optical parametric inverse process, so that the combination of the nonlinear optical medium that causes the optical parametric process, the extraction means (for example, the mirror), and the nonlinear optical medium that causes the inverse process has a different optical intensity. The higher the reflectance, the higher the reflectance. Therefore, it becomes possible to generate short pulse light, and the light generated from the laser medium that is not involved in the optical parametric process is emitted from the extraction means as short pulse light. Further, the light generated in the reverse process returns to the laser medium to cause stimulated emission.

Further, if optical means for correcting group velocity dispersion is arranged on the optical path between the two nonlinear optical media, the generated light in the optical parametric process will have its group velocity dispersion corrected, It is incident on a nonlinear optical medium that causes the reverse process.

In the fourth short pulse laser light source according to the present invention, in addition to the same operation as the third short pulse laser light source, the selective emission means is the generated light in the optical parametric process and is involved in the reverse process. Those not selected are selected and emitted as short pulse light. The light generated in the reverse process does not go out and returns to the laser medium to cause stimulated emission.

In the second and fourth short pulse laser light sources, the rotating means rotates the medium to adjust the orientation of the medium, and the temperature adjusting means adjusts the temperature of the medium.

Further, in the second and fourth short pulse laser light sources, the optical means for correcting group velocity dispersion corrects the group velocity dispersion of the generated light in the optical parametric process.

Further, in the third and fourth short pulse laser light sources, the optical path length adjusting means has an optical path in the resonator so that the generated lights from the laser medium traveling in opposite directions collide with each other in the nonlinear optical medium. Adjust the length.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A short pulse laser light source according to embodiments of the present invention will be described below with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols and redundant description may be omitted.

The first embodiment is an embodiment of the first and second short pulse laser light sources of the present invention. FIG. 1 shows the configuration of a short pulse laser light source according to this embodiment. As shown, a pair of mirrors M ₁ and M ₂ constitutes a laser resonator, and a laser medium 1, a nonlinear optical crystal X and a polarizing element 2 are installed inside the laser resonator. The laser medium 1 is, for example, N
It is composed of a d: YAG laser rod, and the emission wavelength in that case can be λ _OSC = 1064 nm. In addition,
The laser medium 1 is pumped by a light source (not shown).

The polarization element 2 is for making laser oscillation light into light having a plane of polarization parallel to the plane of the paper, which facilitates the optical parametric process in the nonlinear optical crystal X. The nonlinear optical crystal X causes positive and reverse optical parametric processes, and the wavelength of the generated light is variable, which will be described later in detail. Collimating lens L ₁ , L ₂
Is for narrowing the beam of laser light to increase the optical power density and making it enter the nonlinear optical crystal X.

The mirror M ₁ is a total reflection mirror, while the mirror M ₂ is a mirror which selectively reflects light of a specific wavelength. That is, letting R _S1 and R _S2 be reflectances with respect to light having wavelengths λ _S1 and λ _S2 (variable wavelength) generated by the optical parametric process, and _letting R _OSC be reflectance with respect to light having a wavelength λ _OSC (fixed wavelength), the mirror M ₂ , R _S1 and R _S2 are high (reflect light of λ _S1 and λ _{S2 at} a high rate), and R _OSC is low (transmit light of λ _OSC at a high rate). In particular,
When the wavelength λ _OSC of the light from the laser medium 1 is 1064 nm, the reflectance of the mirror M ₂ is as shown in FIG.

Next, the operation of the above embodiment will be described.

First, in the crystal X of FIG. 1 having a non-linear optical effect, the wavelength λ _S1 , in the relationship of 1 / λ _OSC = 1 / λ _S1 + 1 / λ _S2 (1) by the optical parametric process. Two waves of λ _S2 are generated. Then, λ _S1 and λ _S2 can be tuned by changing the angle θ between the crystal axis c of the crystal X and the excitation light of λ _OSC . Here, _assuming that the intensities of the respective waves are I _OSC , I _S1 , and I _S2 , the conversion efficiency η from λ _OSC light to λ _S1 and λ _S2 light by the parametric process is η = (I _S1 + I _S2 ) / I _OSC ……………… (2), the conversion efficiency η is proportional to the light intensity I _OSC in the optical parametric process. That is, the following equation η = κ · I _OSC κ becomes the proportionality constant (3). Therefore, the parametric output is I _S1 + I _S2 = κ · I _OSC ² (4).

At this time, the mirror M ₂ has a low reflectance (R _OSC ) for the wavelength λ _OSC and a high reflectance (R _S1 for the wavelengths λ _S1 and λ _S2 as shown in FIG. , R
_S2 , which is abbreviated as R _S here), the intensity of the light reflected from the mirror M ₂ is R _S1 I _S1 + R _S2 I _S2 = R _S · κ · I _OSC ² (5) .

When the reflected light from the mirror M ₂ , that is, the light having the wavelengths λ _S1 and λ _S2 is incident on the crystal X of FIG. 1 having the nonlinear optical effect again, the parametric process opposite to that described above is performed. Occurs, and light of wavelength λ _OSC is generated. If the conversion efficiency at this time is ξ, the light intensity of the wavelength λ _OSC emitted from the crystal X is ξ · (R _S · κ · I _OSC ² ) ² ………………………… (6 ) Can be described.

From this, in the combination of the nonlinear optical crystal X and the mirror M ₂ , the reflectance with respect to the wavelength λ _OSC changes nonlinearly with α · I _OSC ³ …………………… (7). It can be thought of as a mirror (a mirror that reflects more light at a higher rate).

Since this has the same effect as the mode-locking using the saturable absorbing dye similar to the prior art, it is possible to generate the short pulse light. Moreover, as shown in (7), the combination of the nonlinear optical crystal X and the mirror M ₂ is a saturable absorber having an excellent saturable absorption characteristic. Therefore, it is possible to obtain a short pulse laser beam having a very narrow pulse time width. This short pulse light (wavelength λ _OSC ) is emitted from the mirror M ₂ .

In the case of FIG. 2, when λ _OSC is the oscillation wavelength of 1064 nm of the Nd: YAG laser, the wavelengths λ _S1 and λ _S2 of the light generated by the parametric mode locking are 1800 nm and 2602 nm, for example. When this light enters the optical crystal X and other optical elements, group velocity dispersion occurs due to wavelength dispersion of the refractive index. Therefore, λ _S1 , λ _S2
The timing at which light re-enters the nonlinear optical crystal X is shifted,
The efficiency of the optical parametric reverse process that occurs in the crystal X is reduced. Therefore, if optical means for correcting the group velocity dispersion (a specific form will be described later) is installed on the optical path between the nonlinear optical crystal X and the mirror M ₂ , the efficiency of the optical parametric reverse process is increased, and as a result, The output intensity of the obtained short pulsed light can be increased.

Further, R _S1, R _S2 is low (to transmit light of lambda _S1, lambda _S2 at a high rate.), The R _OSC is (reflects light lambda _OSC at a high rate.) High mirror M ₃ Once installed, λ _S1 , λ _S2
It can also extract light. That is, simultaneous oscillation of three wavelengths of λ _S1 , λ _S2 and λ _OSC is possible. Further, if the phase matching condition is adjusted by changing the direction of the crystal axis of the crystal X or changing the temperature, the wavelengths λ _S1 and λ _S2 can be selected over a wide range, and multiple wavelengths including λ _OSC light are added. It is possible to obtain the short pulse light of. In this embodiment, the wavelength is tunable by operating the rotating means 7 (not shown) to change the direction of the crystal axis.

Next, a first modification of the first embodiment will be described. This is an apparatus in which a nonlinear optical crystal for generating a harmonic of λ _OSC light is installed in the resonator of the short pulse laser light source of the first embodiment shown in FIG. FIG. 3 is a diagram showing the configuration of the apparatus of this modification. This device has
The SHG crystal X ₃ is used as a crystal for generating harmonics. In this device, an optical parametric process is generated with light having a wavelength of λ _SHG (= λ _OSC / 2). Where the second
If the reflectance for higher harmonics is R _SHG , the mirror M
₂ , R _SHG , R _S1 , and R _S2 are high, and R _OSC is low. In contrast, the mirror M ₃ has high R _SHG and R _OSC , and R _S1 ,
R _S2 is low.

When the light of wavelength λ _OSC is incident, the SHG crystal X ₃ produces the second harmonic of its half wavelength λ _SHG . The light of the wavelength λ _SHG enters the nonlinear optical crystal X and causes an optical parametric process. The wavelengths λ _S1 and λ _S2 of the light generated by this process satisfy the relationship of 1 / λ _SHG = 1 / λ _S1 + 1 / λ _S2 (8). Then, the nonlinear optical crystal X and the mirror M
The combination of ₂ can be considered as a mirror in which the reflectance for the wavelength λ _SHG changes nonlinearly with α · I _SHG ³ …………………… (9). Acts as a saturable absorber that reflects. The λ _SHG light reflected by this saturable absorber is SHG
The light enters the crystal X ₃ and generates λ _OSC light, causing laser resonance. In this way, it is possible to output short pulsed light. And since λ _SHG light has a shorter wavelength than λ _OSC light,
As is clear from the equation (8), short pulse light having a wavelength shorter than λ _OSC can be obtained from the mirror M ₃ .

The harmonic generating crystal is not limited to the SHG crystal, and the same effect can be obtained by using, for example, a nonlinear optical crystal that generates the third and fourth harmonics, or a combination thereof. Is obtained.

FIG. 4 is a diagram showing the construction of the apparatus of the second modification of the first embodiment. This device is a laser medium 1
Is a short pulse laser light source using a crystal having a wide oscillation wavelength range such as titanium sapphire (Ti: Al ₂ O ₃ ). In this device, a wavelength selection element 11 (a birefringent filter, a diffraction grating, etc.) is installed in a resonator.

When the generated light from the laser medium passes through the wavelength selection element 11, it becomes light having a spectral width of about several nm centering on λ _OSC within the oscillation wavelength range. Here, λ _OSC can be arbitrarily selected within the oscillation wavelength range. Then, light having this spectral width causes an optical parametric process.

In this device, more modes are locked due to the existence of the above spectral width. Therefore, it is possible to further reduce the pulse time width. FIG. 5 is a configuration diagram of a short pulse laser light source according to the second embodiment. In this case, in addition to the configuration of the first embodiment, a mirror M ₄ and prisms 3 and 4 having a triangular prism shape are installed as optical means for correcting group velocity dispersion in the laser resonator.

The mirror M ₄ is a total reflection mirror and is installed for setting an optical path in the resonator.

As shown in the drawing, the prisms 3 and 4 are installed so that their directions are opposite to each other and the surfaces facing each other are parallel to each other. This prism pair has a λ
It is an optical means for correcting the group velocity dispersion of _S1 and λ _S2 light. The time delay of the λ _S1 and λ _S2 lights caused by the group velocity dispersion causes not only the decrease in the efficiency of the reverse process as described above but also the expansion of the pulse time width of the short pulse light emitted from the mirror M ₃ .
Therefore, in this embodiment, the group velocity dispersion is corrected by installing the prisms in pairs as described above. Therefore, according to the apparatus of this embodiment,
Due to the correction effect of the group velocity dispersion by the prism pair, short pulse light having a narrower pulse time width can be emitted from the mirror M ₃ as compared with the case where no correction is made. In this case, the installation is not limited to the position shown in FIG. 5, but the correction can be made at any position on the optical path, and the λ _S1 and λ _S2 light is incident even outside the resonator. If it is installed at the position, the same effect can be obtained. Moreover, you may install a plurality in the above-mentioned positions. Further, by installing a prism pair as an optical means for correcting the group velocity dispersion on the optical path between the nonlinear optical crystal X and the mirror M ₂ , the efficiency of the reverse process is increased, and λ _S1 , λ _S2 light and λ _OSC light The output intensity of can be increased.

Also, the second embodiment can be modified in the same manner as the first embodiment, and the same effect can be obtained.

The third embodiment is an embodiment of the third and fourth short pulse laser light sources of the present invention. FIG. 6 shows a short pulse laser light source according to this embodiment. In this short pulse laser light source, the laser resonator in the short pulse laser light source of the first embodiment is configured in a ring type. As shown in the drawing, the laser resonator is formed by the mirrors M ₁ , M ₂ and M ₃ , and the laser medium 1 is provided inside this. The mirror M ₂ is an extracting means and selects the emission wavelength λ _OSC from the laser medium 1 and outputs it to the outside. Further, the lenses L ₁ and L ₂ enter the light having the increased optical power density into the nonlinear optical crystals X ₁ and X ₂ . And the crystal X ₁
Causes the optical parametric process, and the crystal X ₂ causes the reverse process. Further, the lenses L ₃ and L ₄ return the light emitted from the crystal X ₂ to the original beam diameter, and the mirror M ₃ is a selective emission means, and the light of the wavelength λ _OSC among this light is emitted from the laser medium 1. It is reflected toward and is output to the outside as light of wavelengths λ _S1 and λ _S2 .

The unidirectional device 5 provided in the optical path is an element that transmits light in only one direction, and is also called an optical isolator or an optical diode, and a Faraday element is generally used. Here, the unidirectional device 5 is not always necessary, but if provided, the light in the opposite direction can be eliminated, and thus unnecessary disturbance between the modes can be reduced.

Next, the operation of the above embodiment will be described.

The beam emitted from the laser medium 1 (wavelength λ
_OSC ) passes through the unidirectional device 5, is reflected by the mirror M ₁ , and the power density is increased by the lenses L ₁ and L ₂ to increase the nonlinear optical crystal X.
Incident on ₁ . As a result, two beams of wavelengths λ _S1 and λ _S2 are generated in the crystal X ₁ by the parametric process.

The light intensities I _S1 and I _S2 of the respective wavelengths λ _S1 and λ _S2 at this time can be expressed as I _S1 + I _S2 = κ · I _OSC ² (10). The mirror M ₂ has the characteristics of R _OSC : ˜0 (small) R _S1 , R _S2 : R _S (large), and therefore the light intensity after reflection is R _S1 · I _S1 + R _S2 · I _S2 = R _S · (I _S1 + I _S2 ) = R _S · κ · I _OSC ² ………………………… (11).

In the second non-linear optical crystal X ₂ , λ _S1 , λ _S2 → λ _{OSC are established} by the reverse optical parametric process of the _first crystal X ₁ , and the original wavelength λ _OSC is restored. The light intensity at that time is represented by I _OSC (after X ₂ ) = ξ · (R _S · κ · I _OSC ² ) ² = α · I _OSC ⁴ (12).

In this way, the light of wavelength λ _OSC emitted from the crystal X ₂ passes through the lenses L ₃ and L ₄ to have the original beam diameter, is reflected by the mirror M ₃ and returns to the laser medium 1. Therefore, in the combination of crystal X ₁ → mirror M ₂ → crystal X ₂ , the transmittance is represented by α · I _OSC ³ …………………… (13), and the higher the incident intensity, the better. Since it can be considered as a mirror that reflects light, that is, a saturable absorber, it is possible to generate short pulsed light. Moreover, since this has an excellent saturable absorption characteristic as shown in (13), it is possible to obtain a short pulse light having a very narrow pulse time width. Further, simultaneous oscillation of three wavelengths of λ _S1 , λ _S2 and λ _OSC is possible. Here, the crystal X ₁ and the crystal X
If the phase matching condition is adjusted by changing the direction of the crystal axis or changing the temperature with respect to ₂ , the wavelengths λ _S1 and λ _S2 can be selected over a wide range, and a short pulse of multiple wavelengths including λ _OSC light can be added. It is possible to get light. In this embodiment, the wavelength is tunable by interlocking the rotating means 8 and 9 (not shown) to change the directions of the crystal axes of the crystals X ₁ and X ₂ . At this time, if one crystal undergoes a normal process, the other one must undergo a reverse process, so that adjustment is made in consideration that if one crystal axis direction is determined, the other crystal axis direction is also determined. There is a need.

In the above embodiment, the mirror M ₃ is the selective emission means (transmits the λ _S1 and λ _S2 lights at a high rate and reflects the λ _OSC light at a high rate). For example, this is a perfect reflection mirror. However, it is possible to obtain short pulse light. in this case,
Only the λ _OSC light exits the mirror M ₂ .

In the first embodiment, since only one nonlinear optical crystal is used, λ _OSC by the optical parametric positive process is used.
Conversion efficiency from light to λ _S1 , λ _S2 light (which depends on κ) and conversion efficiency from λ _S1 , λ _S2 light to λ _OSC light by optical parametric reverse process (this depends on ξ .)
The combination of the values of is determined by the type of nonlinear optical crystal. On the other hand, in the present embodiment, since the crystal for the forward process and the crystal for the reverse process are separated, it is possible to select the combination of κ and ξ, and thereby the desired short pulse light The output intensity can be further increased.

As in the case of the first embodiment, the λ _S1 and λ _S2 lights generated in the third embodiment have different group velocities in the process of passing through the respective optical elements. Therefore, in the fourth embodiment, as shown in FIG. 7, optical means (for example, the above-mentioned prism pair) for correcting the group velocity dispersion is installed on the optical path between the crystals X ₁ and X ₂ . For this reason, the efficiency of the optical parametric reverse process is increased and the output intensity of the short pulse light obtained as a result can be increased for the reason described in the first embodiment.

[0053] The third, the apparatus of the fourth embodiment, lambda _S1 mirror M ₃ as a selection output means, when outputting the lambda _S2 light, lambda _S1, group velocity dispersion of the lambda _S2 light is emitted In this case, λ _S1 and λ _S2 light appear as a time delay, and as a result, the pulse time width increases. This is as described in the second embodiment. Therefore, similarly to the second embodiment, the prism pair for correcting the group velocity dispersion is installed on the optical path inside the resonator or at the position where the emitted λ _S1 and λ _S2 light enters even outside the resonator. And correct the time delay of λ _S1 and λ _S2 light,
Short pulse light having a narrower pulse time width can be emitted from the mirror M ₃ .

FIG. 8 shows a fifth embodiment.
In this device, the unidirectional device 5 is removed from the configuration of the third embodiment, and the optical path length adjusting means 10 is installed instead. Then, a configuration is shown in which the λ _OSC light travels in both directions on the optical path, and each is mode-locked by the optical parametric process to shorten the pulse.

In this apparatus, the optical path length adjusting means 10 comprises total reflection mirrors M ₅ and M ₆ and a right-angle prism 6. The total reflection mirrors M ₅ and M ₆ are arranged in a _V shape so that the optical path direction and the normal direction of each mirror surface intersect each other at an angle of 45 degrees. The right-angled prism 6 is a prism having a triangular prism shape having a bottom surface of an isosceles right triangle, and of the surfaces forming the triangular prism, two surfaces including the isosceles side of the bottom surface and perpendicular to the bottom surface cause total reflection. Further, the right-angle prism 6 is variable in the vertical direction in the figure so that the optical path length can be adjusted arbitrarily. According to this, the light that has entered one of the mirrors is reflected perpendicularly to the incident direction and enters the prism.
The light changes its direction in the prism, enters the other mirror perpendicularly to the incident direction, is reflected by the mirror, and travels in the incident direction again. In this way, as the light passes through the prism, the optical path length of this light becomes long. Further, the optical path length can be arbitrarily increased by changing the position of the rectangular prism 6.

By using this, the optical path length is adjusted so that the clockwise and counterclockwise pulsed lights shown in the figure collide with, for example, the nonlinear optical crystal X _1. The non-linear effect at the time of collision is further increased, and the intensity of the generated light at the crystal X ₁ is increased. As a result, the intensity of the short pulsed light also increases. Since the unidirectional device 5 has been removed, there is a concern about the disturbance between the modes that travels in both directions as described above, but generally, the effect of shortening the pulse is greater when the non-linear effect is increased rather than suppressing the disturbance between the modes. large. Therefore, in this embodiment, the pulse time width can be made narrower. The position of the optical path length adjusting means 10 is not limited to the position shown in FIG. 8 and may be any position on the optical path. Moreover, the above-mentioned thing is only an example as an optical path length adjusting means, and another optical path length adjusting means may be used.

[0057] Further, although the selection output means the mirror M ₃ in FIG. 8, the mirror M ₃ are as short pulse laser light source
May be, for example, a total reflection mirror, in which case only λ _OSC light is emitted from the mirror M ₂ as short pulse light.

FIG. 9 shows a sixth embodiment, which is a pair of prisms for correcting group velocity dispersion on the optical path between the crystals X ₁ and X ₂ in the short pulse laser light source of the fifth embodiment. Is installed. Also in this case, the efficiency of the optical parametric reverse process can be increased and the output intensity of the obtained short pulsed light can be increased, as in the above-described embodiment.

Further, in both the fifth and sixth embodiments, the mirror M
₃ lambda _S1 as selecting the exit means, when outputting the lambda _S2 light, the group velocity dispersion optical path in the resonator a correction prism pair or cavity outside the A and was also emitted lambda _S1,, lambda _S2 By installing the light at a position where light is incident and correcting the time delay of the λ _S1 and λ _S2 lights, short pulse light with a narrower pulse time width can be emitted from the mirror M ₃ .

The present invention is not limited to the above-described embodiment. For example, similarly to the second embodiment, in the short pulse laser light sources of the fourth and sixth embodiments, a prism pair is further provided for each optical element. A plurality of prism pairs may be provided as a whole by installing the prism pairs. Further, in the above embodiment, the triangular prism pair is used as the optical means for correcting the group velocity dispersion, but the optical means for correcting the group velocity dispersion is not limited to this. Also, the third, fourth, fifth and sixth
The same modifications as in the first embodiment are possible in the embodiment. However, when performing the first variant, each optical path between the laser medium 1 and the optical path and the laser medium 1 between the nonlinear optical crystal X ₁ and the nonlinear optical crystal X _2, the crystals for harmonic generation Install. At this time, each of the harmonic generating crystals generates a harmonic when the generated light from the laser medium is incident, and the harmonic generating when the other harmonic generating crystal is incident. It is oriented so that it causes the reverse process of development. The fifth, when performing a second modification to the sixth embodiment, each optical path between the laser medium 1 and the optical path and the laser medium 1 between the nonlinear optical crystal X ₁ and the nonlinear optical crystal X ₂ Then, a wavelength selection element is installed.

The method of the above embodiment can be applied to a solid-state laser excited by a semiconductor laser, an excimer laser, and a gas laser, and the type of laser is selected depending on the wavelength range to be obtained.

[0062]

As described above in detail, according to the first short pulse laser light source of the present invention, the saturable absorber is composed of the nonlinear optical medium having the optical parametric action and the extracting means. , The light emitted from the laser medium is reflected at a higher rate as the light intensity is higher, and the ratio of this reflectance to a higher rate according to the light intensity (saturable absorption characteristic) is excellent, and the pulse time width is extremely high. A short pulse laser light source that generates a narrow short pulse light can be realized. Further, if the optical means for correcting the group velocity dispersion is arranged on the optical path between the nonlinear optical medium and the extracting means, the generated light in the optical parametric process is
After correcting the group velocity dispersion, it is possible to correct the timing deviation and re-enter the nonlinear optical medium, so that a short pulse laser light source with high output can be realized.

Further, according to the second short pulse laser light source of the present invention, since the selective emitting means is provided in addition to the first short pulse laser light source, the light of the wavelength of the generated light in the optical parametric process is provided. Can also be emitted as short pulsed light. Furthermore, if the phase matching condition is adjusted by changing the direction of the non-linear optical medium by rotating means or changing the temperature condition by the temperature adjusting means, it becomes possible to select the wavelength of the emitted short pulse light, and the wavelength tunable A short pulse laser light source can be realized.

Further, according to the third short pulse laser light source of the present invention, since the non-linear optical medium that causes the optical parametric process is provided separately from the non-linear optical medium that causes the optical parametric process, By selecting each medium, the conversion efficiency in the forward process and the reverse process can be independently selected, and a short pulse laser light source with high output can be realized. Further, if the optical means for correcting the group velocity dispersion is arranged on the optical path between the nonlinear optical medium for the optical parametric positive process and the nonlinear optical medium for the inverse process, the generated light in the optical parametric process is After correcting the velocity dispersion, the deviation of the timing can be corrected and the light can be incident on the nonlinear optical medium for the reverse process, so that a short pulse laser light source with high output can be realized.

Further, according to the fourth short pulse laser light source of the present invention, since the selecting means is provided in addition to the third short pulse laser light source, it is the same as the second short pulse laser light source for the first. The effect is obtained.

Further, in the second and fourth short pulse laser light sources, if the optical means for correcting the group velocity dispersion is appropriately arranged, the group velocity dispersion of the generated light in the optical parametric process is corrected and the generated light is corrected. Since the time delay of is corrected, it is possible to obtain a short pulse light with a narrower pulse time width.

Further, in the third and fourth short pulse laser light sources, if the optical path length adjusting means is provided, the laser resonance lights traveling in opposite directions are caused to collide with each other in the non-linear optical medium so that a non-linear effect is produced. Since it can be increased, it is possible to obtain a short pulse light having a narrower pulse time width.

According to the single pulse laser light source as described above, several tens ps (picoseconds) to several ps, and further fs
(Femtosecond) order wavelength tunable short pulse laser light is obtained. Therefore, it can be widely used in the field of high-speed or precise optical measurement.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a short pulse laser light source according to a first embodiment.

FIG. 2 is a characteristic diagram of a mirror M ₂ .

FIG. 3 is a configuration diagram of a short pulse laser light source of a first modified example of the first embodiment.

FIG. 4 is a configuration diagram of a short pulse laser light source according to a second modification of the first embodiment.

FIG. 5 is a configuration diagram of a short pulse laser light source according to a second embodiment.

FIG. 6 is a configuration diagram of a short pulse laser light source according to a third embodiment.

FIG. 7 is a configuration diagram of a short pulse laser light source according to a fourth embodiment.

FIG. 8 is a configuration diagram of a short pulse laser light source according to a fifth embodiment.

FIG. 9 is a configuration diagram of a short pulse laser light source of a sixth embodiment.

FIG. 10 is an explanatory diagram of a conventional example.

[Explanation of symbols]

1 ... Laser medium, 2 ... Polarizing element, 3, 4 ... Prism, 5
... Unidirectional device, 6 ... Right angle prism, 7, 8, 9 ... Rotating means,
10 ... optical path length adjusting means, 11 ... wavelength selection element, X ... nonlinear optical medium, M _2, M ₃ ... wavelength selective mirror.

Claims (12)

[Claims] 1. A laser medium, a laser resonator having the laser medium therein, a nonlinear optical medium provided inside the laser resonator, and light generated from the laser medium is incident on the nonlinear optical medium. An optical parametric generated in the non-linear optical medium by re-incident by the re-incident by the extracting means. A short pulse laser light source characterized in that light generated in a reverse process is fed back to the laser medium. 2. The optical means for correcting the group velocity dispersion of the generated light in the optical parametric process is arranged on the optical path between the nonlinear optical medium and the extracting means. Short pulse laser light source. 3. A laser medium, a laser resonator having the laser medium inside, a nonlinear optical medium provided inside the laser resonator, and light generated from the laser medium is incident on the nonlinear optical medium. Extraction means for selectively extracting the generated light in the optical parametric process that occurs when the light is re-entered to the nonlinear optical medium, and the generated light in the optical parametric process that is re-incident by the extracting means. Selective emission means for selecting one that does not participate in the optical parametric reverse process occurring in the nonlinear optical medium and emitting it from the resonator, so that the generated light in the optical parametric reverse process is fed back to the laser medium. A short pulse laser light source characterized by the above. 4. The short pulse laser light source according to claim 3, further comprising rotating means for rotating the nonlinear optical medium. 5. The short pulse laser light source according to claim 3, further comprising temperature adjusting means for adjusting the temperature of the nonlinear optical medium. 6. A laser medium, a laser resonator having the laser medium therein, and a first laser light provided inside the laser resonator for generating an optical parametric process by incidence of generated light from the laser medium. A nonlinear optical medium of
Extraction means for selectively extracting the generated light in the optical parametric process, and a second nonlinear optical medium that causes an optical parametric reverse process by incidence of the generated light in the optical parametric process extracted by the extracting means. A short pulse laser light source, characterized in that the generated light in the optical parametric reverse process is fed back to the laser medium. 7. An optical means for correcting group velocity dispersion of light generated in the optical parametric process is provided on an optical path between the first nonlinear optical medium and the second nonlinear optical medium. The short pulse laser light source according to claim 6. 8. A laser medium, a laser resonator having the laser medium therein, and a first laser light provided inside the laser resonator for generating an optical parametric process by incidence of light generated from the laser medium. A nonlinear optical medium of
Extraction means for selectively extracting the generated light in the optical parametric process, and a second nonlinear optical medium that causes an optical parametric reverse process by incidence of the generated light in the optical parametric process extracted by the extracting means. , Selection of light generated in the optical parametric process occurring in the first nonlinear optical medium, which is not involved in the optical parametric reverse process occurring in the second nonlinear optical medium, and emitted from the resonator A short pulse laser light source, comprising: an emitting unit, and the generated light in the optical parametric reverse process is fed back to the laser medium. 9. A rotating means for rotating the first non-linear optical medium and a rotating means for rotating the second non-linear optical medium, both of which are operated in an interlocking manner. Short pulse laser light source. 10. The short pulse laser light source according to claim 8, further comprising temperature adjusting means for adjusting the temperatures of the first and second nonlinear optical media. 11. An optical path length adjusting means for adjusting an optical path length in the resonator is provided, and generated lights from the laser medium traveling in opposite directions along the optical path collide in a nonlinear optical medium. 6. The method according to claim 6, 7, 8, 9 or 1.
The short pulse laser light source described in 0. 12. The method according to claim 3, further comprising one or more optical means for correcting group velocity dispersion of generated light in the optical parametric process.
1. The short pulse laser light source described in 1.