JPH0875603A - Optical response measuring instrument - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide an optical response measuring instrument capable of operating in the visible region to the near infrared region with a time resolution of about ps to 10 fs or less. [Structure] The output light of a laser 1 is incident on an optical parametric oscillator 4 via second and third harmonic generators 2 and 3, and one of signal light and idler light is selected by a wavelength filter to select an optical Kerr shutter system 8. Incident on. 2 with beam splitter 9
The beam is divided into beams A and B, reflected by the mirrors 10 to 12 and the corner reflectors 13 and 14, passed through the half-wave plates 15 and 16, the polarizers 17 and 18, and the lens 19 to be focused on the sample 20. The light enters the spectroscope 23 through the analyzer 21 and the lens 25, is detected by the light receiver 22, and enters the boxcar integrator 26. The position of 26 is adjusted by the pulse stage 24.
4 and 26 are controlled by the computer 27.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a measuring device for response time of optical materials and devices, which is capable of operating over a wide wavelength range and has a time resolution much shorter than the pulse width of a light source. is there.

[0002]

2. Description of the Related Art The response time of optical materials and devices including non-linear optical materials is measured by using a short pulse laser which is faster than the response time. So far, stable and wavelength-variable picosecond and subpicosecond light sources have been limited to composite mode-locked dye lasers that are synchronously pumped by mode-locked lasers such as Ar ion lasers and Nd ³⁺ : YAG lasers.
Recently, a Ti: Al ₂ O ₃ laser has been used as a wavelength tunable sub-picosecond or femtosecond light source. However, the usable oscillation wavelength range Δλ is
It is about Δλ to 10 nm with a dye laser and about Δλ to 100 nm with a Ti: Al ₂ O ₃ laser. Further, changing the oscillation wavelength requires not only replacing the gain medium and the saturable absorber in the dye laser, but also changing the optical components such as the mirror, which is a troublesome work. Also, Ti: A
Even in the case of the l ₂ O ₃ laser, in order to keep the time width of the optical pulse constant, it is necessary to keep the dispersion in the laser cavity unchanged, and it is limited to the oscillation wavelength range of 700 nm ≦ λ ≦ 1000 nm. Even so, the optical components have to be changed within the range of Δλ to 100 nm.

On the other hand, light that cannot maintain coherence is called incoherent light. This incoherent light is
For example, even if the pulse width is nanoseconds or more, the spectral width of light is wider than the value corresponding to the pulse width, and the coherence time is extremely short on the picosecond or sub-picosecond order. Therefore, it can be seen that the time resolution corresponding to this coherence time can be obtained even with a light source having a wide pulse width. Therefore, in the case of the incoherent light pulse and the ultrashort light pulse whose pulse widths are considerably different from each other, in the case of measurement using the pulse correlation, they can be treated equivalently from the viewpoint of coherence time (T. Yajim).
a, N .; Morita, "Method of Lase"
r Spectroscopy. "Y. Prior,
A. Ben-Reuven, and M.M. Rosenb
luh, eds. (Plenum, New York,
1986), pp 75-85). The measurement of the relaxation time using this incoherent light is also called incoherent spectroscopy, and it was used for the measurement of the phase relaxation time that requires an ultrafast optical pulse (Y. Ishida and T.Y.
ajima, Rev. Phys. Appl. 22, 16
29 (1987)). In reality, there are more reports using picosecond laser light rather than nanosecond laser. For example,
When a picosecond or subpicosecond pulse is incident on an optical fiber or the like, the spectrum width increases due to the self-phase modulation effect. As an example of using this chirp pulse as a light source, there is a report by Nakano et al. (H. Nakano, Y. Ishi.
da, and T.S. Yanagawa, Appl. Ph
ys. Lett. 59, 3090 (1991)). This incoherent spectroscopy technique has considerably eased the labor required to generate extremely short light pulses, which has been extremely difficult until now, but the spectral width obtained is still the same as the output light of a picosecond or subpicosecond laser. Even if it is adopted as the excitation light, it is at most about several tens of nm, and the time resolution corresponding to this spectral width is at most about several tens of fs.

From the above, the conventionally used optical response measuring instrument can be used only in the wavelength range and the time resolution range which are limited by the light source and the optical components used, and the picosecond and subpicosecond light sources, respectively. Even if is used, the spectral width of 100 nm at the most, from several 10 fs to 1
The time resolution is about 00 fs. On the other hand, an optical response measuring device that uses the output light from the optical parametric converter as an incoherent light source (Japanese Patent Application No. 4-2402).
70, JP-A-6-94571), even if a nanosecond optical pulse is used as an excitation light source, the optical response in the picosecond to subpicosecond region can be easily measured. However, we can measure non-resonant (without absorption) nonlinear optical response such as electronic effect and molecular orientation effect.
In order to understand the characteristics of all-optical high-speed switches, an optical Kerr (Ker
r) A shutter arrangement is desirable.

On the other hand, the pump-probe method is often used for measuring the lifetime of a photoexcited carrier that determines the resonance type nonlinear optical response. However, in measuring the carrier lifetime, changes in the transmittance of probe light are observed. Therefore, in the degenerate pump-probe method, leak light of pump light often deteriorates S / N. In this respect, the non-degenerate pump-probe method is advantageous, but it is not easy to prepare short-pulse light sources having different wavelengths or obtain an incoherent light source having the same coherence. In this point, when the optical parametric converter is used, photon pairs (signal light and idler light) having the same coherence can be easily obtained in different wavelength regions.

[0006]

As described above, the conventional optical response measuring instrument has a spectral width of 100 nm at most and a few tens of fs even if a picosecond or subpicosecond light source is used.
It is about time resolution. Morita et al. Found that when using a nanosecond light source with a pulse width of about 2-3 ns, the spectral width was 0.02-0.2 nm and the time resolution was several ps even when using incoherent spectroscopy. (N. Morita, T. Tokizak).
i, and T. Yajima. J. Opt. Soc.
Am. B 4,1296 (1987)). Moreover, the oscillation wavelength range that can be used as the light source is 100 nm or less.

The object of the present invention is to extend the usable wavelength from the visible region to the near infrared region and to improve the time resolution from ps to 10 fs.
It is to provide an optical response speed measuring device whose degree is less than or equal to a certain degree, and in particular to provide a polarization rotation type (optical Kerr shutter system) response measuring device that can be used in a form in which a non-resonance type nonlinear optical response is separated. is there.

Further, in order to improve the S / N and measure the wavelength dependence of carrier dynamics, a non-degenerate pump-probe method is expected even though it is difficult to secure a light source. Another object of the present invention is to provide a plurality of incoherent light beams having different coherences with different wavelengths simply by using optical parametric conversion light beam as incoherent light beam in the non-degenerate pump-probe method. is there. Thereby, the resonance type nonlinear optical response such as carrier lifetime can be measured.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[0010]

In order to achieve the above-mentioned object, the optical response measuring instrument of the solving means of (1) of the present invention is such that the polarization axes of optical media having a nonlinear refractive index effect are orthogonal to each other. In a nonlinear optical device sandwiched by two polarizers arranged, an output light from an optical parametric converter including at least one of an optical parametric oscillator, an optical parametric amplifier, and an optical parametric fluorescence generator is used as a light source. It is characterized by using.

An optical response measuring device as a means for solving (2) of the present invention is the optical response measuring device according to (1), further comprising means for separating output light of the optical parametric converter.
The output light is separated into signal light and idler light, and only one of the lights is used.

An optical response measuring device as a solution means of (3) of the present invention is the optical response measuring device according to (1), further comprising means for separating output light of the optical parametric converter.
The feature is that the light is separated into the signal light and the idler light, and both lights are coaxially used.

The optical response measuring device of the solution means (4) of the present invention is the optical response measuring device according to any one of (1) to (3), wherein the output light of the optical parametric converter is: It is characterized in that a dichroic mirror is provided as means for separating or multiplexing.

The optical response measuring device of the solution means (5) of the present invention is the optical response measuring device according to (2), wherein the means for separating the output light of the optical parametric converter is a wavelength filter. Is characterized by.

The optical response measuring device as the means for solving the problem (6) of the present invention is capable of adjusting the delay time of at least one light beam by injecting a plurality of light beams into an optical medium having a nonlinear absorption effect. In the nonlinear optical device, the output light from the optical parametric converter including at least one of an optical parametric oscillator, an optical parametric amplifier, and an optical parametric fluorescence generator is used as a light source.

An optical response measuring device as a means for solving (7) of the present invention is the optical response measuring device according to (6), further comprising means for separating the output light of the optical parametric converter.
The output light is separated into a signal light and an idler light, one of which is used as a pump light (excitation light) having a high light intensity, and the other is used as a probe light for adjusting a delay time with respect to the pump light.

An optical response measuring device according to a solution of (8) of the present invention is the optical response measuring device according to (6), further comprising means for separating output light of the optical parametric converter.
The output light is separated into signal light and idler light, and both lights are coaxially arranged for use.

[0018]

According to the above-mentioned means, when the optical parametric conversion using the BBO crystal is used for the excitation light of 355 nm, the short wavelength limit is 450 nm or less, the long wavelength limit is 1700 nm or more, and Δλ to 1250 nm.
A wide wavelength tunable light source as described above can be realized. Even if the nanosecond light pulse is used as the excitation light, the time resolution of the present invention is several ps or less. If a picosecond light source is used, an optical response speed measuring method and a measuring instrument therefor capable of time resolution of 10 fs or less can be realized. When the output light of the optical parametric converter is incident on a wide-band optical amplifier to be optically amplified, an optical response measuring device with a wider variable wavelength can be obtained at a higher speed. In this way, a time resolution of several ps to several 10 fs can be obtained in the range of 400 nm to 3000 nm.

The above-mentioned wide wavelength tunable region and narrow time resolution are achieved by the optical parametric converter (optical parametric oscillator (OPO), optical parametric amplifier (OPA), optical parametric fluorescence generator (OPF)) and incoherent spectroscopy method. Can be realized by using simultaneously. For example, considering an optical parametric oscillator, if the angular frequency of the pumping light is ω ₃ , the angular frequency of the signal light generated by the optical parametric effect is ω ₁ , and the angular frequency of the idler light is ω ₂ , then ω ₃ = ω ₁ + ω ₂ is established. At this time, for example, in a negative uniaxial crystal such as BBO (β-BaB ₂ O ₄ ),

[0020]

[Equation 1]

Is satisfied. However, e and o represent an extraordinary ray and an ordinary ray, respectively, n ₃ is the refractive index of the excitation light, and n _{2 is}
Represents the refractive index of idler light, and n ₁ represents the refractive index of signal light. The gain width δω at this time is

[0022]

[Equation 2]

It is represented by Here, L is the crystal length and c is the speed of light. The phase change φ of light in the crystal can be expressed as φ = knL, where k is the propagation constant of light. At this time, the group delay time τ _g is

[0024]

(Equation 3)

[0025] Therefore, from (2) and (3)

[0026]

(4) δω = 2π / | τ _1g −τ _2g | (4) is obtained.

[0027]

[Outer 1]

[0028]

(Equation 5)

Is obtained.

[0030]

[Outside 2]

And the refractive index n at the phase matching angle θ
It is obtained from the λ derivative of the relational expression of (θ) and n _o and n _e , and the expression (3). The Sellmeier equation and its λ derivative are shown in the following equations (6) and (7), respectively, and the relational expression of the refractive index and its λ derivative are also shown in the equations (8) and (9).

[0032]

(Equation 6)

For example, using BBO (β-BaB ₂ O ₄ ), the third harmonic (355n) of an Nd ³⁺ : YAG laser is used.
m) When excitation is performed, the phase matching angle θ becomes about 30 ° in order to obtain signal light at a wavelength near 488 nm. At this time, the group delay time difference between the signal light and the idler light is (3)
And can be calculated using the equations (6) to (9) and 215fs
/ Mm is obtained. When the length of the BBO crystal is 12 mm, it becomes a large value of δν = 4 THz. This value means that a time resolution of about 200 fs can be obtained when the incoherent spectroscopy method is used.

To measure the optical response time, the emission intensity of photoluminescence is time-resolved and the decay time is observed, or two beams of laser light incident on the sample are used.
Alternatively, a transient grating is configured with three beams, and the decay time of the diffracted light intensity and the recovery time of the nonlinear absorption are observed by the pump / probe method. In incoherent spectroscopy, these decay time and recovery time, the energy relaxation time T _{1 of} the sample, and the phase relaxation time T ₂
The relationship between the pulse width t _p and the coherence time t _c of the light pulse, it, the spectral width of the optical transition in the excitation light wavelength of the magnitude relationship and a sample of T _1, T ₂ is, depending on whether homogeneous or heterogeneous It has been decided. The results and theoretical examinations by each experimental arrangement are discussed in detail in the reports as shown below (N. Morita, T. Yajim).
a, Phys. Rev. A 30, 2525 (198
4); Morita, T .; Tokizaki, an
d T. Yajima, J, Opt. Soc. Am. B
4, 1269 (1987): A. W. Weine
r, S. De Silvervestri, and E.M. P.
Ippen, J .; Opt. Soc. Am. B 2,65
4 (1985)).

According to the present invention, the output light of the optical parametric converter is used as incoherent light to form an optical Kerr shutter system and a two-wavelength non-degenerate pump / probe system, and as described above, a high speed is achieved in an extremely wide wavelength variable range. The response time measuring instrument of was realized. Further, when the output light of the optical parametric converter is incident on an optical amplifier having a gain width approximately the same as the spectral width of the output light of the optical parametric converter, the response time of the response time measuring device can be obtained without impairing the time resolution of the incoherent spectroscopy. The measurement sensitivity can be improved.

[0036]

Embodiments of the present invention will be described below in detail with reference to the drawings.

[Embodiment 1] FIG. 1 is a block diagram showing a schematic configuration of a spatially arranged optical Kerr shutter system as an embodiment of the optical response time measuring device of the present invention. Lasers used include Q-switched Nd ³⁺ : YAG laser (Q-YAG),
High output mode-locked Nd ³⁺ : YAG laser (ML-YA
In addition to G) and Ar lasers, titanium sapphire lasers (Ti: Al ₂ O ₃ ) and collision pulse mode-locked dye lasers (CPM) are also conceivable if the pulsed light output is amplified. Here, it is assumed that a peak power of several MW or more is secured, and an example of using Q-YAG, which is the easiest to perform maintenance work, will be shown. Of course, the following can be similarly realized as long as the laser has an output capable of wavelength conversion, including the lasers mentioned here. Used Q-Y
The AG laser has a pulse energy of 600 mJ, a pulse width of 15 ns, and a repetition frequency of 10 Hz. The output light (fundamental wave) of the laser 1 is first made incident on a second harmonic generator (SHG) 2 using a nonlinear optical crystal such as CD ^* A.
The pulse energy of SH wave of Q-YAG is 140mJ,
The pulse width is about 12 ns. The output second harmonic (SH wave) and the transmitted light of the fundamental wave are incident on the third harmonic generator (THG) 3 using a nonlinear optical crystal such as KD ^* P, and the third harmonic is generated by the sum frequency generation. Obtain harmonics (TH waves). Q
The pulse energy of the -YAG TH wave is 90 mJ, and the pulse width is about 10 ns. Only the obtained TH wave is B
It is incident on an optical parametric oscillator (OPO) 4 using a non-linear optical crystal such as BO, and O
Obtained as PO output photon pairs. The sum of the outputs of the signal light and the idler light is 15 mJ, and the pulse width is about 8 ns.
Here, the oscillation wavelength variable range of the OPO is widened from the visible range to the near-infrared range, and the use of the TH wave, which makes it easier to set the wavelength using the angle phase matching, will be described. Can be used without any problem. One of the photon pairs of the OPO output is selected by the wavelength filter 5, is totally reflected by the prism (p) or the 45 ° incident total reflection mirror (M) 6, 7 and is incident on the optical Kerr shutter system 8. Here, a two-beam spatial arrangement type system is shown, and the difference between the polarization directions of the two beams A and B is 45 °. In this case, the signal light,
The optimum one is selected depending on which one of the idler light is used, and only one wavelength is made incident on the degenerate four-wave mixing system 8. Instead of the wavelength filter, an optical component having a wavelength selecting function such as a dispersion prism may be used. The OPO output is divided into two beams A and B by the beam splitter (BS) 9.
45 ° incidence total reflection mirrors 10 to 1
It is reflected by 2 or the corner reflectors (CR) 13 and 14, passes through the half-wave plates 15 and 16 and the polarizers 17 and 18, and is focused on the sample 20 by the lens (L) 19. The corner reflector may be a prism depending on the time resolution used. It is desirable to insert the half-wave plate and the polarizer into both the A and B optical paths in order to avoid the influence of the dispersion change due to the difference in the optical paths as much as possible. Fresnel ROM is used for the half-wave plate to obtain a wide wavelength tunable range. Here, the polarizations of the beam A and the beam B are inclined by 45 ° with respect to each other, as indicated by the circles in FIG. When the beam A is the probe light and the beam B is the gate light, the probe light after passing through the sample 20 has only the polarization component orthogonal to the polarization direction before passing cut out by the analyzer 21, and is output to the photomultiplier tube (PMT). Typical light receiver 22
Detected in. The spectroscope 23 removes stray light and outputs S /
Although N is improved, it may be omitted if the noise component is almost negligible. The position of the corner reflector 14 is controlled by the pulse stage (PS) 24,
The delay time τ _d of the probe light with respect to the gate light is adjusted. A lens 25 is used to enter the probe light after passing through the sample, that is, the signal light S, into the spectroscope 23. The output of the photomultiplier tube 22 is input to a boxcar integrator (BCI) 26 and a blotter, and the intensity change of S is recorded. The boxcar integrator 26 and the pulse stage 24 are controlled by a computer 27. Since the OPO output is used as incoherent light as described above, it is possible to easily measure picosecond and subpicosecond response times.

FIG. 2 shows CS ₂ when the method of the present invention is used.
The waveform of the optical car shutter output of is shown. If the delay time of the probe light is taken on the horizontal axis, the response speed of the substance to be measured can be obtained. FIG. 3 shows the measurement result of the response time. The horizontal axis represents the delay time of the probe light (optical path A), and the vertical axis represents the signal light intensity. In FIG. 2, a nanosecond output pulse waveform reflecting the excitation light waveform is observed.
When the change in the intensity of the signal light S is measured while moving,
As shown in FIG. 3, the correlation waveform of the OPO incoherent pulse is obtained. The tail of the correlation waveform of the pulse is overlapped with the response derived from the electronic effect of the sample and the relaxation of the molecular orientation,
Overlaid on a _d independent background. In FIG. 3, a response of picosecond order is seen, but this is because the correlation waveform of the pulse is dominant, and the response waveform of the sample is not clear. This is because the measurement is performed on the short wavelength side of 490 nm, so that the OPO gain width is narrow and the time resolution is on the order of picoseconds. FIG. 4 shows the wavelength dependence of the gain width of the BBO-OPO used in this example. Idler light is omitted because it is the same as the corresponding signal light. As is clear from this figure, the sub-picosecond correspondence of the sample can be easily obtained by performing the same experiment in the vicinity of 600 nm.

The spectral width δλ shown in FIG. 4 is 488.
nm is about 0.3 nm, and δν = 0.4 THz. This value agrees with the value of the time resolution of the response speed measurement described above, but is one digit smaller than the calculated value of δν described in the section "Action". This is because the time resolution is determined by the photon lifetime determined by the reflectance of the OPO resonator mirror. When light reciprocates in the optical resonator in this way, the bandwidth becomes narrower. Therefore, when the resonator structure is abolished and the traveling wave type is used, naturally, from the above results,
The time resolution becomes short. Since there is a trade-off relationship between the time resolution and the output power of the optical parametric conversion light, whether the resonator is assembled or the traveling wave type is used satisfies the conditions imposed on the sample and the measuring instrument. You can select it.

Since a wide gain band is required for amplification of the incoherent light source, an optical parametric amplifier or a wide wavelength band solid-state amplifier represented by titanium sapphire (Ti: Al ₂ O ₃ ) can be used. . At the insertion points of these optical amplifiers, the OPO output light is the optical car shutter system 8
Immediately before entering.

[Embodiment 2] FIG. 5 shows an optical Kerr shutter system in which gate light and probe light are coaxially arranged. The optical components used are the same as in the case of Example 1 shown in FIG. In Example 1, the interaction length between the non-linear optical medium and the light is at most several mm, although it varies depending on the intensity of the incident light and the angle formed by the incident light. In the second embodiment, this interaction length can be made longer than that of the first embodiment, so that the S / N becomes high, and even if the nonlinearity is small, the response speed can be improved by adopting the form of the capillary, the waveguide, or the fiber. Can be measured. The light source part is basically the same as that of the first embodiment, but in this system, light of two wavelengths (signal light and idler light) near the degeneration point of the OPO is used. As long as wavelength separation is possible, two incoherent light beams having the same coherence but different wavelengths can be obtained, so that the optical Kerr shutter having the above-mentioned time resolution can be obtained. As a matter of course, also in the first embodiment, the same result can be obtained by allocating either the signal light or the idler light to the gate light or the probe light to assemble the experimental system.

In the yarn of FIG. 5, the laser 1, the second harmonic generator 2, the third harmonic generator 3 and the optical parameter transmitter 4 are used as in FIG. 1, but the OPO output signal light and idler are used. The light is assigned to either the gate light or the probe light, separated by the wavelength separation dichroic mirror 28, and is incident on the thread 30 of the optical car shutter. Example 1
Similarly, the separated light is reflected by the mirrors 9 to 12 and 33 or the corner reflectors 13 and 14, and both are polarized. Further, in order to suppress the difference in chromatic dispersion as much as possible, the half-wave plates 15 and 16 and the polarizers 17 and 18 are transmitted. The delay time τ _d of the probe light with respect to the gate light is adjusted by controlling the position of the corner reflector (CR) 14 by the pulse stage (PS) 24 and the computer 27. In FIG. 5, the same arrangement is used for the gate light. The gate light is p-polarized or s-polarized. The polarization of the probe light is rotated by 45 ° from the polarization of the gate light, and is incident on the dichroic mirror 32 for wavelength multiplexing together with the gate light. The emitted light (the probe light is transmitted and the gate light is reflected) is condensed on the sample 20 by the lens 19. The light that has passed through the sample is incident on the wavelength separation filter or dichroic mirror 31, and is transmitted through the analyzer 21. Since the removal of the gate light is indispensable here, the wavelength filter and the dichroic mirror 31 are arranged immediately after the sample. 31 may be placed after the analyzer 21. The polarization direction of the analyzer 21 is orthogonal to the polarization of the probe light before entering the sample. The dichroic mirror 31 reflects the gate light after passing through the sample. Only the polarization component of the analyzer 21 is cut out from the probe light that has been polarized and rotated by the intensity of the gate light and has passed through the sample.
The light enters the spectroscope 23 through 5 and is detected by the photomultiplier tube 22. If the S / N is sufficient, the spectroscope is not necessary. The output of the photomultiplier tube 22 is input to a boxcar integrator (BCI) 26 and a blotter, and the intensity change of S is recorded. The boxcar integrator 26 and the pulse stage 24 are controlled by the computer 27. As a result, for example, the signal light is 674 for the TH wave of Q-YAG.
nm, the idler light is 750 nm, the signal light is 1.0 μm for the SH wave, and the phase resolution is performed at an arbitrary wavelength in the vicinity of the idler light 1.14 μm. This enables time-resolved spectroscopy faster than the response.

For amplification of the OPO incoherent light source,
As described above, an optical parametric amplifier is used because it requires a wide gain band and two-wavelength amplification. The insertion point of this optical amplifier is just before the OPO output light is incident on the optical Kerr shutter system, and the normal input light is pump light (here, TH wave or SH wave of Q-YAG) and signal light or idler light. Is either.

[Third Embodiment] In the first and second embodiments, the configuration example of the response measuring device using the optical Kerr shutter is described. Here, the configuration of the optical response measuring instrument concerning the method of measuring the carrier lifetime of the resonant nonlinear optical material using the pump-probe method is described. Basically, the configuration is almost the same as in the first and second embodiments. The reference numerals assigned to the optical components are shown in FIG.
And FIG. 5 are common. Japanese Patent Application No. 4-240270
As described in (Japanese Patent Application No. 6-94571), the carrier lifetime can be measured by the two-beam OPO incoherent method in which one optical path is provided with a time delay. The carrier lifetime measuring device shown in FIG. 6 is similar to that shown in FIG. 1 except that the laser 1, the second harmonic generator 2, the third harmonic generator 3, and the optical parametric oscillator 4 are used.
However, the wavelength filter 5 is omitted. Here, the output light of the optical parametric converter 4, that is, either the signal light or the idler light having different wavelengths is described above.
It is assigned to each of the beams, namely the pump light or the probe light. A dichroic mirror 28 is used to separate the signal light and the idler light. A prism or a diffraction grating may be used instead of the dichroic mirror. The two beams thus separated are separated by the dichroic mirror 2
8. It is introduced into the pump / probe experiment system 30 by a folded mirror 29 (or a prism). The introduced two beams are reflected by the mirrors 9 to 12 or the corner reflectors 13 and 14 and focused on the sample 20 by the lens 19. Carrier life, that is, energy relaxation time T ₁
Is obtained from the recovery time of the transmittance change ΔT. Since the transmitted light intensity is measured, the background transmittance T ₀ when pump light is not incident
On top of the probe light transmittance change ΔT when pump light is incident
Are superposed with the background signal of incoherent spectroscopy. A dichroic mirror 31 is used to remove the pump light that acts on the S / N, but other than this, a wavelength filter, a reflection mirror, a pinhole, a slit, or the like can be used. To focus the two beams on the sample 20, reflection by a concave mirror may be used. A lens 19 as shown in FIG. 6 is used to focus the two beams on the sample 20, but it is also possible to use reflected light from a concave mirror instead of using the lens. The probe light after passing through the sample 20, that is, the signal light is incident on the spectroscope 23 and detected by the photomultiplier tube 22. The output of the photomultiplier tube 22 is input to a boxcar integrator (BCI) 26 and a blotter, and the intensity change of S is recorded. The boxcar integrator 26 and the pulse stage 24 are controlled by a computer 27.

As described above, T ₁ can be measured by dividing the incoherent light obtained by using the optical parametric conversion into two and using it as the light source of the pump-probe method. This is the method first shown by Tomita et al. Using a Q-switch mode-locked YAG laser (Q-ML-YAG) (M. Tomita, M. Matsu).
oka, J .; Opt. Soc. Am. B 3,560
(1986)). When a coherent laser pulse is used as the pump light and an optical parametric conversion light output with a wide spectral width is used as the probe light with a time delay, the time-resolved spectrum can be obtained by measuring the intensity of the probe light after passing through the sample. Can be measured. In this case, since the sample transmitted light of the probe light having a wide spectrum width can be measured, the probe light delay time dependency of the carrier relaxation process over a wide wavelength range can be expected. For example, Ti:
Picosecond and femtosecond pulsed light of Al ₂ O ₃ laser
i: Amplified by an Al ₂ O ₃ amplifier, and the output light after this amplification is divided into two. One is used as pump light and the other is incident on the second harmonic generator, and optical parametric conversion is performed with the obtained SH wave. When this optical parametrically converted light is used as the probe light, the time-resolved spectrum can be observed and the carrier relaxation process over a wide wavelength range can be overlooked.

[Embodiment 4] FIG. 7 shows a carrier lifetime measuring system in which pump light and probe light are coaxially arranged. The optical components used are the same as in FIGS. 1, 5 and 6. The light source part is basically similar to the configuration shown in FIG. That is, the separated light is reflected by the mirrors 9 to 12, 33 or the corner reflectors 13 and 14, and in this system, O
Two wavelengths of light (signal light and idler light) near the PO degeneracy point are used. As long as wavelength separation is possible, two incoherent light beams having the same coherence but different wavelengths can be obtained, so that the pump / probe system having the above-mentioned time resolution can be obtained.

The OPO output signal light and idler light are
It is assigned to either pump light or probe light and is separated by the dichroic mirror 28 for wavelength separation. The separated two beams are introduced into a pump / probe experiment system 30 by a dichroic mirror 28 and a folding mirror 29.
The separated light is reflected by the mirrors 9 to 12, 33 or the corner reflectors 13 and 14, and the polarization of the probe light is rotated by 45 ° from the polarization of the pump light by the polarizer 16.
The light enters the dichroic mirror 32 for wavelength multiplexing together with the pump light. The delay time τ _d of the probe light with respect to the pump light is adjusted by controlling the position of the corner reflector (CR) 14 by the pulse stage (PS) 24 and the computer 27. The emitted light (the probe light is transmitted and the pump light is reflected) is condensed on the sample 20 by the lens 19.
As described in Example 3, a concave mirror can be used instead of the lens for condensing the two beams. The light transmitted through the sample 20 again enters the wavelength separation filter or dichroic mirror 31. A plurality of 31 may be provided if necessary. The pump light after passing through the sample is reflected by the dichroic mirror 31. Although the dichroic mirror 31 is used to remove the pump light, a wavelength filter, a reflection mirror, a pinhole, a slit, or the like can be used instead. The probe light after passing through the sample, in which the transmittance changes depending on the intensity of the pump light, passes through the lens 25 to the spectroscope 2.
3 and is detected by the photomultiplier tube 22. Incidentally, if the S / N is sufficient, the spectroscope is not necessary. The output of the photomultiplier tube 22 is the boxcar integrator (BC
I) It is input to 26 or a blotter and the intensity change of S is recorded. The boxcar integrator 26 and the pulse stage 24
Are controlled by the computer 27.

The wavelength used may be exactly the same as in the third embodiment. The amplification of OPO incoherent light is also the same as in the third embodiment.

[0049]

As described above, according to the present invention, the output light from the optical parametric converter including at least one of the optical parametric oscillator, the optical parametric amplifier, and the optical parametric fluorescence generator is used as the light source. 450nm to 1700 by using
It has become possible to measure the optical response time by using the optical Kerr shutter and the pump-probe method in a wide wavelength range of up to nm. Moreover, even if a nanosecond laser is used as an excitation light source, only a BBO crystal of about 12 mm is used,
A time resolution of picoseconds to subpicoseconds or less can be realized. If the crystal length is further shortened or the resonator structure is stopped and the traveling wave type is adopted, the response time of the phenomenon can be measured even faster. Thus, there is no optical response time measuring instrument that is simple and can continuously use light in a wide wavelength range and has sufficiently short time resolution. Recently, a pulsed laser with a high output and a short pulse width has been vigorously developed, and a titanium sapphire laser (Ti: Al
_Even femtosecond lasers such as ₂ O ₃ ) have come into practical use. Especially Ti: Al ₂ O ₃ is OPO by SH wave.
Not only that, but because the pulse width is short, high peak power can be obtained with a small amount of amplification, and time resolution can be dramatically improved. In the future, the present invention will elucidate the high-speed light phenomenon and in various application fields utilizing the high-speed light phenomenon,
Expected to make a major contribution.

In particular, H. M. An optical bistable device proposed by Gibbs et al. (HM Gibbs, G.G.
R. Olbright. N. Peyghambaria
n. H. E. Schmidt, S .; W. Koch, an
d H. Haug, Phys. Rev. A 32, 69
2 (1985)), a high-speed optical switch using the optical Kerr effect, and distortion correction of an optical image using a phase conjugate wave (RK Jain and RC Lind, J. et al.
Opt. Soc. Am. 73, 647 (1983)),
Generation of ultrashort optical pulses using saturable absorption characteristics, suppression of quantum noise by optical squeezing (RE Sluth
her, L .; W. Hallberg, B.A. Yurke,
J. C. Mertz, and J.M. F. Valley,
Phys. Rev. Lett. 55, 2409 (198
5)) and other materials, which are indispensable for the application of nonlinear optics and quantum optics, and which provide high-speed and large nonlinear optical effects, and EO sampling materials, the optical response speed of the sample is used. Since measurement is important, it has been earnestly desired that a fast response time of sub-picosecond can be continuously measured using only one measurement system over a wide wavelength range from the visible region to the near infrared region. For this purpose, it is only necessary to use the ultrashort light pulsed laser light easily, but in reality, generation and application of the ultrashort light pulse requires a great deal of time and labor of a highly skilled engineer. Will be. According to the present invention, even with Q-switched (nanosecond) laser light that is almost maintenance-free, a high-speed response time ranging from picoseconds to subpicoseconds, and even femtoseconds, can be obtained from the visible range to near red. It is possible to continuously measure using only one measuring system over a wide wavelength range up to the outer region.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an optical response time measuring instrument using OPO incoherent light of Example 1 of the present invention.

FIG. 2 is a diagram showing an example of measuring an output waveform of a CS ₂ optical car shutter by OPO incoherent spectroscopy,
(A) corresponds to the case where the gate light is on (ON), and (b) corresponds to the case where the gate light is off (OFF).

FIG. 3 is a diagram showing probe light delay time dependence of CS ₂ optical Kerr shutter output by the OPO incoherent spectroscopy shown in FIG.

FIG. 4 is a diagram showing an example of spectrum width measurement of signal light of BBO-OPO.

FIG. 5 is a block diagram showing a schematic configuration of a coaxial arrangement type optical car shutter using an OPO incoherent light source of Example 2 of the present invention.

FIG. 6 is a two-wavelength light (signal light and idler light) obtained from the OPO incoherent light source according to the third embodiment of the present invention.
FIG. 3 is a block diagram showing a schematic configuration of a pump / probe experiment system using the above.

FIG. 7 is a block diagram showing a schematic configuration of a coaxially arranged pump / probe system using signal light and idler light obtained from an OPO incoherent light source of Embodiment 4 of the present invention.

[Explanation of symbols]

 1 Laser (Q-YAG) 2 2nd Harmonic Generator (SHG) 3 3rd Harmonic Generator (THG) 4 Optical Parametric Oscillator (OPO) 5 Wavelength Filter (Including Optical Intensity Attenuator) 6,7, 10-12 45 ° incidence total reflection mirror 8 optical Kerr shutter system 9 beam splitter (BS) 13,14 corner reflector (CR) 15,16 half-wave plate 17,18 polarizer 19,25 lens 20 sample 21 analyzer (18 22) Photomultiplier tube (PMT) 23 Spectrometer 24 Pulse stage (PS) 26 Boxcar integrator (or plotter) 27 Computer A, B Light beam

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshikuni Kaino, 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Inside Nippon Telegraph and Telephone Corporation (72) Inventor, Yuzo Ishida 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation

Claims (8)

[Claims] 1. An optical response measuring instrument for measuring a nonlinear refractive index effect of an optical medium, wherein an optical medium having a nonlinear refractive index effect is sandwiched between two polarizers arranged so that polarization axes thereof are orthogonal to each other. An optical response measuring instrument, characterized in that the output light from an optical parametric converter, which includes at least one of an optical parametric oscillator, an optical parametric amplifier and an optical parametric fluorescence generator, is used as a light source. 2. The optical response measuring device according to claim 1, further comprising means for separating output light of the optical parametric converter, and separating the output light into signal light and idler light,
An optical response measuring instrument characterized in that only one of the lights is used. 3. The optical response measuring device according to claim 1, further comprising means for separating output light of the optical parametric converter, separating the light into signal light and idler light, and arranging both lights in a coaxial arrangement. An optical response measuring instrument characterized by being used. 4. The optical response measuring device according to claim 1, further comprising a dichroic mirror as a means for separating or combining the output light of the optical parametric converter. And an optical response measuring instrument. 5. The optical response measuring device according to claim 2, wherein the means for separating the output light of the optical parametric converter is a wavelength filter. 6. An optical response measuring instrument for measuring a nonlinear absorption effect of an optical medium by injecting a plurality of light beams into an optical medium having the nonlinear absorption effect and adjusting a delay time of at least one light beam. An optical response measuring instrument, characterized in that the output light from the optical parametric converter is used as a light source and includes at least one of an optical parametric oscillator, an optical parametric amplifier and an optical parametric fluorescence generator. 7. The optical response measuring device according to claim 6, further comprising means for separating output light of the optical parametric converter, and separating the output light into signal light and idler light,
An optical response measuring instrument, wherein one is used as a pump light (excitation light) having a high light intensity and the other is used as a probe light for adjusting a delay time with respect to the pump light. 8. The optical response measuring device according to claim 6, further comprising means for separating output light of the optical parametric converter, and separating the output light into signal light and idler light,
An optical response measuring instrument characterized in that both lights are coaxially used.