JPH04111484A - Method of generating fourth harmonics of nd:yag layer - Google Patents

Abstract

PURPOSE:To get the fourth harmonics in the condition of being stable for a long time even without performing the temperature control of third nonlinear optical crystals by constituting the third nonlinear optical crystals out of LiB3O5 crystals. CONSTITUTION:Third nonlinear optical crystals 7, to which the third harmonics near to near ultraviolet-rays regions enter and which emit the fourth harmonics, are made of LiB3O5 crystals, where the self absorption of ultraviolet rays are little and the allowable temperature range of phase conformity condition is wide. Hereby, the third nonlinear optical crystals 7 are subject to thermal influence, and the phase conformity condition goes out of order, and the refractive index changes, and light intensity scarcely drops, and even without performing the temperature control of the third nonlinear optical crystals 7, the fourth harmonics of Nd:YAG laser can be gotten in the condition of being stable for a long time.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention provides a fourth harmonic generation method of Nd: YAG laser used in fields such as laser chemistry, laser lithography, laser medicine, and biotechnology that require high-power ultraviolet rays. It is related to.

[Conventional technology] Traditionally, in the fields of laser chemistry, laser lithography, laser medicine, biotechnology, etc., depending on the purpose,
Harmonic waves are generated and utilized from a laser beam, and the procedure for generating harmonic waves is shown in FIG.

In Fig. 4, l is a Nd: YAG laser (neodymium doped YAG laser) oscillator, and 2 is a CD*A crystal (C
3 is a first nonlinear optical crystal made of a BBO crystal (β-BaB20a crystal), or a second nonlinear optical crystal made of a KD P crystal (KD2PO4 crystal), etc.
4 is a 60″ dispersion prism.

When a BBO crystal is used as the second nonlinear optical crystal 3, the BBO crystal is cut so that the angle ψ is 0'' and the phase matching angle θ is 48''.

Further, when a KD P crystal is used as the second nonlinear optical crystal 3, the KD P crystal is cut so that the angle ψ is 45° and the phase matching angle θ is 90°.

Note that ψ and θ refer to the following angles.

That is, as shown in Figure 3, the refractive index of light of the crystal is n
Assuming X, y, and Z axes where nX x n17 < n7 where X and nysn7, the angle formed by the projection of a vector extending in any direction through the origin onto the X-y plane with the X-axis is ψ, and the angle between the two axes of the vector is θ.

In the above configuration, when a fundamental wave (wavelength λ1=1.0B42Jffi) is emitted from the Nd:YAG laser oscillator l, the fundamental wave is incident on the first nonlinear optical crystal 2, and based on the relationship The optical crystal 2 converts a part of the fundamental wave to the second harmonic (wavelength λ2-0.5a21m)
occurs.

Further, the second harmonic and the fundamental wave transmitted through the first nonlinear optical crystal 2 enter the second nonlinear optical crystal 3, and based on the relationship, the second harmonic and the fundamental wave transmitted through the first nonlinear optical crystal 2 are
Part of the harmonics to the fourth harmonic (wavelength λa = 0.2B
6 μs) is generated, and the fourth harmonic, the fundamental wave and the second harmonic that have passed through the second nonlinear optical crystal 3 are incident on the 606 dispersion prism 4, and the 60° dispersion prism 4
The separated harmonics are then used for a specific purpose.

[Problems to be Solved by the Invention] However, when a KDP crystal is used as the second nonlinear optical crystal 3, the second harmonic is more sensitive than the fundamental wave, and the fourth harmonic is more sensitive than the second harmonic. Since the wave is closer to the near-ultraviolet region, the KDP crystal is thermally affected by the self-absorption of the ultraviolet light, which disturbs the phase matching condition and changes the refractive index, as shown in Figure 2. Approximately 20 minutes after starting 1, the normalized output decreases and the light intensity reaches 0, so the Nd:
It is not possible to obtain the fourth harmonic of YAG laser.

In addition, even when a BBO crystal is used as the second nonlinear optical crystal 3, the phase matching condition is disturbed due to self-absorption of ultraviolet light, as in the case of the KDP crystal described above, although not as much as in the case of the KDP crystal, as shown in Fig. 2. As shown in the figure, the normalized output decreases with the passage of time after starting the Nd: YAG laser oscillator 1, so when using the KD'''P crystal, the Nd: 4th YAG laser
Can't get harmonics.

For this reason, conventionally, the heating temperature of the second nonlinear optical crystal 3 was adjusted using a temperature control device, but it was difficult to maintain the second nonlinear crystal 3 at a constant temperature.

The present invention solves the above-mentioned problems.
The purpose is to be able to obtain harmonics in a stable state for a long time.

[Means for Solving the Problems] The present invention makes the fundamental wave emitted by a Nd:YAG laser oscillator enter a first nonlinear optical crystal, and the first nonlinear optical crystal converts a part of the fundamental wave into a second wave. A harmonic is generated, the second harmonic and the fundamental wave that has passed through the first nonlinear optical crystal are made incident on a second nonlinear optical crystal, and a part of the fundamental wave is generated by the second nonlinear optical crystal. A third harmonic is generated from a part of the second harmonic, and the third harmonic, the fundamental wave transmitted through the second nonlinear optical crystal, and the second harmonic are converted into LiB.
The third nonlinear optical crystal is made of a 505 crystal, and the third nonlinear optical crystal generates a fourth harmonic from a part of the fundamental wave and a part of the third harmonic.

[Function] When the Nd: YAG laser oscillator is activated to emit a fundamental wave, the fundamental wave is incident on the first nonlinear optical crystal, and the first nonlinear optical crystal converts a part of the fundamental wave into a second wave. Harmonics are generated and the remaining fundamental wave is transmitted through the first nonlinear optical crystal.

The second harmonic and the fundamental wave transmitted through the first nonlinear optical crystal are incident on the second nonlinear optical crystal, and the second harmonic and the second harmonic are partially transmitted through the second nonlinear optical crystal. The third harmonic is generated from the second harmonic, and the remainder of the fundamental wave and second harmonic are transmitted through the second nonlinear optical crystal.

The third harmonic, the fundamental wave, and the second harmonic that have passed through the second nonlinear optical crystal are incident on the third nonlinear optical crystal, and
The fourth harmonic is generated from a part of the fundamental wave and a part of the third harmonic by the third nonlinear optical crystal, and the fundamental wave, the remainder of the third harmonic, and the second harmonic are generated by the third harmonic. Transmits through 3 nonlinear optical crystals.

In the present invention, the third nonlinear optical crystal, into which the third harmonic near the near ultraviolet region is incident, and which emits the fourth harmonic, has low self-absorption of ultraviolet light and has a temperature tolerance range of phase matching conditions. Since it is composed of a wide LiB50s crystal,
The third nonlinear optical crystal is affected by heat, the phase matching condition is disturbed, the refractive index changes, and the decrease in light intensity is very small.
The fourth harmonic of the Nd:YAG laser can be obtained in a stable state for a long time without controlling the temperature of the third nonlinear optical crystal.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of an apparatus for carrying out the method of the present invention, in which 1 is a Nd:YAG laser oscillator, 4 is a 60@ dispersion prism, 5 is a first nonlinear optical crystal, and 6 is a second nonlinear optical crystal. Optical crystal 7 indicates a third nonlinear optical crystal.

Nd: Fundamental wave emitted by YAG laser oscillator (
λ1 = 1.0Ei42Jal) can be incident on the first nonlinear optical crystal 5 whose angle of the BBO crystal is cut to ψ-〇'', θ-48'', and the fundamental wave is generated by the first nonlinear optical crystal 5. The second harmonic (λ2
-0.5321gIl), and the remaining fundamental wave that has passed through the first nonlinear optical crystal 5, is transferred to a second nonlinear optical crystal 6, which is obtained by cutting the LiB505 crystal at an angle of ψ-37.8" and an angle of θ-90°. The third harmonic (λ3−0.3547 μm) generated from a part of the fundamental wave and a part of the second harmonic by the second nonlinear optical crystal 6 and the second nonlinear optical The remaining fundamental wave and second harmonic that have passed through the crystal 6 are transferred to the LiB50s crystal at an angle of ψ-60.
7@, third nonlinear optical crystal 7 cut to θ-90″
The fourth harmonic (λa = 0.266uR) generated from a part of the fundamental wave and a part of the third harmonic by the third nonlinear optical crystal 7 and the third nonlinear optical The remaining fundamental wave, second harmonic wave, and third harmonic wave that have passed through the crystal 7 are allowed to enter the dispersion prism 4 at 60@.

In the above configuration, when the Nd:YAG laser oscillator I is activated and emits a fundamental wave (λ+ -1,0842 m), the fundamental wave is incident on the first nonlinear optical crystal 5, and the fundamental wave is incident on the first nonlinear optical crystal 5. 5, the second harmonic (λ2-0.5321
Jal) is generated, and the remainder of the fundamental wave is transmitted through the first nonlinear optical crystal 5.

The second harmonic and the fundamental wave transmitted through the first nonlinear optical crystal 5 enter the second nonlinear optical crystal 6, and the second harmonic and the second harmonic are transmitted through the second nonlinear optical crystal 6. Based on the relationship from part of the wave, i3 harmonic (λ3−.0.3547n
) is generated, and the rest of the fundamental wave and second harmonic are transmitted through the second nonlinear optical crystal 6.

The third harmonic, the fundamental wave, and the second harmonic that have passed through the second nonlinear optical crystal 6 are incident on the third nonlinear optical crystal 7, and the third harmonic is transmitted through the third nonlinear optical crystal 7. The fourth harmonic (λ4−
0.2667 m) is generated, and the fundamental wave, the remainder of the third harmonic, and the second harmonic are transmitted through the third nonlinear optical crystal 7.

Furthermore, the fourth harmonic and the remaining fundamental wave, second harmonic, and third harmonic that have passed through the third nonlinear optical crystal 7 are 60@
The light enters the dispersion prism 4 and is separated by the 60° dispersion prism 4 into a fundamental wave, a second harmonic, a third harmonic, and a fourth harmonic.

In the present invention, the third nonlinear optical crystal 7, into which the third harmonic near the near ultraviolet region is incident and which emits the fourth harmonic, has low self-absorption of ultraviolet light and has a permissible temperature range of phase matching conditions. Since the third nonlinear optical crystal 7 is formed of a Li8305 crystal with a wide range of Even without controlling the temperature of the crystal 7, Nd:Y remains stable for a long time as shown in Figure 2.
The fourth harmonic of the AG laser can be obtained.

Note that the fourth harmonic generation method of the Nd:YAG laser of the present invention is not limited to the above-mentioned embodiments.
Of course, various changes can be made without departing from the spirit of the invention.

[Effects of the Invention] As explained above, according to the fourth harmonic generation method of the Nd:YAG laser of the present invention, various excellent effects as described below can be achieved.

(1) The third nonlinear optical crystal, into which the third harmonic near the near ultraviolet region is incident, and which emits the fourth harmonic, has low self-absorption of ultraviolet light and a wide allowable temperature range for phase matching conditions.
Since it is composed of iB50s crystal, the third nonlinear optical crystal is affected by heat, the phase matching condition is disturbed, the refractive index changes, and the decrease in light intensity is very small, and the temperature of the third nonlinear optical crystal is The fourth harmonic of the Nd:YAG laser can be obtained in a stable state for a long time without any control.

■ The second harmonic passes through the second and third nonlinear optical crystals, and the third harmonic passes through the third nonlinear optical crystal, so the fundamental wave of the Nd:YAG laser and the second, third,
Four wavelengths of the fourth harmonic can be obtained simultaneously.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram showing an example of an apparatus for carrying out the method of the present invention, FIG. 2 is a graph showing the stability of light intensity of a nonlinear optical crystal that wavelength converts the fourth harmonic of a Nd:YAG laser, and FIG. FIG. 3 is a conceptual diagram of a phase matching angle of a nonlinear optical crystal, and FIG. 4 is a conceptual diagram showing an example of a conventional Nd:YAG laser device. In the figure, l is Nd: YAG laser oscillator, and 5 is the first
, 6 is a second nonlinear optical crystal, 7 is W
! 3 shows a nonlinear optical crystal of No. 3. Kajo e5Agu

Claims (1)

[Claims] 1) The fundamental wave emitted by the Nd:YAG laser oscillator is incident on a first nonlinear optical crystal, and the first nonlinear optical crystal generates a second harmonic from a part of the fundamental wave. The wave and the fundamental wave transmitted through the first nonlinear optical crystal are incident on a second nonlinear optical crystal, and the second nonlinear optical crystal converts a part of the fundamental wave and a part of the second harmonic into
A third harmonic is generated, and the third harmonic, the fundamental wave transmitted through the second nonlinear optical crystal, and the second harmonic are transferred to LiB_3.
The Nd is made incident on a third nonlinear optical crystal made of O_5 crystal, and the third nonlinear optical crystal generates a fourth harmonic from a part of the fundamental wave and a part of the third harmonic. : Fourth harmonic generation method of YAG laser.