JPH0480980A - Optical element and laser resonator - Google Patents

Abstract

PURPOSE:To enable a laser device to be controlled in vertical mode and polarization mode of laser rays and to maintain a stable laser oscillation low in noise by a method wherein a mode control plate possessed of an etalon effect and a wave plate effect is inserted in the resonator of a laser device provided with a nonlinear optical material. CONSTITUTION:An optical film whose reflectivity R is so set as to satisfy a formula, FO = piR<1/2>/(1-R) (FO denotes finesse when laser ray passes through an optical element once), is provided to a light input-output face. The film concerned is polished to be as thick as L, where L is so set as to satisfy a formula, O<L<=<=L1 = C/(2n.FSR) (where, (m) denotes a natural number, lambdais the wavelength of laser rays, (C) represents speed of light, (n) is the refractive index of an optical element, FSR represents the free spectrum space of an optical element, and (a) means a minimum) and the film is made not to serve as a lambda/4 wave plate but as a lambda/2 wave plate.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a laser resonator into which a novel single mode control element is inserted.

[Prior art] Conventionally, when generating harmonics by inserting a nonlinear optical material into a laser resonator, the noise and output fluctuations that occur are
It is reduced by inserting an etalon or a wave plate into the resonator to control the intra-cavity mode.

However, inserting two types, an etalon and a wave plate, into the resonator increases the loss within the resonator. In addition, it occupies a large volume and cannot be used for small resonators. Since alignment is performed separately, it is difficult to adjust the position, and there are problems such as a large number of parts (which makes the structure complicated and reliability reduced).

[Problems to be Solved by the Invention] An object of the present invention is to overcome the above-mentioned drawbacks of the prior art.

[Means for Solving the Problems] The present invention provides a light input/output surface with a reflectance R of Fo:πR""
An optical film is formed that satisfies / (1-R) (where Fo is the finesse when the laser passes through the optical element once), and the thickness L is 0<L≦L, = c/ (2n-F
SR) (However, m is a natural number, e is the wavelength of the laser,
An optical element which is polished to become a λ/2 plate within the range of C: high speed, n: refractive index of the optical element, FSR: free spectral interval of the optical element, and a: minimum value;
And the reflectance R on the light input/output surface is F0=πR””/
An optical film is formed that satisfies (1-R) (where Fo is the finesse when the laser passes through the optical element once),
Thickness is 0<L≦L, = c/ (2n-FSR)
(However, m is a natural number, e is the wavelength of the laser, C is the high speed, n is the refractive index of the optical element, FSR is the free spectral interval of the optical element, and a is the minimum value.) It is provided by being polished.

Hereinafter, the present invention will be explained according to embodiments. FIG. 1 shows a sectional view of the basic configuration of the present invention.

In Figure 1, 1 is a solid laser medium, and 2 is Ti0P.
A nonlinear optical material such as an O4 crystal, 3 a mode control plate having both the effects of an etalon and a wave plate, and 4 an output mirror. In FIG. 1, one end face of the solid-state laser medium is used as a resonant mirror of a laser resonator, but it is also possible to provide a resonant mirror 5 as shown in FIG. 2. It is also possible to change the arrangement of 2 and 3 in FIG. 1 and the arrangement of 1.2.3 in FIG.

[Function] This is shown for a Nd:YAG laser with a laser resonator length Lc=5c+w. The gain spectrum width (oscillation region) of the Nd:YAG laser at room temperature is 250 GHz, and the etalon free spectral spacing (FSR; F
Since single-mode oscillation is not possible unless the ray 5pectral range is wider than the laser oscillation range, the FSR of the etalon is set to 250 GHz. At this time, the thickness of the etalon is n is the refractive index of the etalon material,
If C is the speed of light, FSR=c/ (2nL), then n
= 1.5, then L = 0.4 mm. Since the function as an etalon can be obtained by setting L≦0.4μm, it is sufficient to set L≦c/(2n·FSR).

Longitudinal mode spacing Δν of the laser resonator. is the cavity length Lc
This is because =5cm. In order to transmit only one longitudinal mode of the laser, the bus band width Δν5 of the etalon is changed by the longitudinal mode spacing Δ
If we take l/10 of 1/(, then the required etalon finesse F will be: However, if the same photon passes through the etalon nine times by resonating in the laser resonator, then
The finesse is (21/l-1) -1'2 times thicker (approximately p is as follows).

The decay time (photon lifetime) of the resonator mode is τ.

Then, Lc c (a Lc + (1-(RIR2)"")
) α: In-cavity loss = 5% R,, R2: Laser resonator end face reflectance = 99.5%
From Z e :3.3 x 1O-8 (sec), p=
C1: c / L c = 198 times, (21/+9
11-1)-1/2 item 17.

From the above, the finesse F0 of the etalon during a single pass can be F0=F/n=833/17=49. From this, the reflectance R of the etalon is F0=πR””/(
Using 1-R), R → 94%. Such an optical film can be obtained by designing and depositing alternating multilayer films of TiO2 and 5i02 to have a reflectance of 94% using the dielectric multilayer film deposition method, which is a method for producing reflective mirror films in an extremely reflective manner. It will be done.

The effect of the wave plate (χ/2.λ/4 plate) is that L is 0.4 mm.
A crystal plate with the following thickness λ = 11064n (N d:
(In the case of a YAG laser), this can be obtained by polishing while monitoring the passing light and finishing the polishing when it reaches a thickness that functions as a wavelength plate.

[Example] A cross-sectional view of the basic configuration of the present invention is shown in FIG. length 5c
A laser resonator of m was fabricated. Mode control board 3 is 11
The material and thickness are designed to exhibit two effects: an etalon for single longitudinal mode oscillation and a wavelength plate (λ/4 plate) that generates a phase difference of λ/4 for the 064n Nd:YAG laser beam. For example, the coating is designed using quartz crystal to a thickness of about 0.4non, polished in the order of the wavelength, and then coated with a dielectric multilayer film so that the finesse in a single pass is about 50 or more. It was produced by

In this case, the intra-resonator loss was set to be 0.5% or less.

[Effects of the Invention] The present invention combines the effects of an etalon and a wave plate.
By newly submitting this one mode control plate and inserting it into the resonator of a laser that has a nonlinear optical material in the resonator, the longitudinal mode and polarization mode of the laser can be controlled to achieve low noise and high Stable laser oscillation is possible. Conventionally, similar effects were obtained by using an etalon and a wave plate separately, but the present invention combines the effects of an etalon and a wave plate.
By using a small, thin crystal plate, it is possible to insert the laser into an ultra-small laser resonator, and excellent effects such as simplification of optical axis alignment and improvement of laser reliability have been recognized.

[Brief explanation of drawings]

1 and 2 are cross-sectional views of embodiments of the basic configuration of the device of the present invention. 1...Solid laser medium 2...Nonlinear optical material 3...Mode control plate No.? figure

Claims (4)

[Claims] (1) The reflectance R on the light input/output surface is F_o=πR^1^
An optical film is formed that satisfies /^2/(1-R) (where F_o is the finesse when the laser passes through the optical element once), and the thickness L is 0<L≦L_1=c/(2n・FS
R) (where m is a natural number, λ is the wavelength of the laser, c is the high speed,
An optical element characterized in that it is polished to become a λ/2 plate within the range of (n is the refractive index of the optical element, FSR is the free spectral interval of the optical element, and a is the minimum value). (2) The reflectance R on the light input/output surface is F_o=πR^1^
An optical film is formed that satisfies /^2/(1-R) (where F_o is the finesse when the laser passes through the optical element once), and the thickness L is 0<L≦L_1=c/(2n・FS
R) (where m is a natural number, λ is the wavelength of the laser, c is the high speed,
An optical element characterized in that it is polished to become a λ/4 plate within the range of (n is the refractive index of the optical element, FSR is the free spectral interval of the optical element, and a is the minimum value). (3) In a laser resonator having a laser medium and a nonlinear optical material arranged between two laser resonant mirrors, the optical element according to claim 1 is arranged on the optical axis within the laser resonator. A laser resonator featuring: (4) In a laser resonator having a laser medium and a nonlinear optical material arranged between two laser resonant mirrors, the optical element according to claim 2 is arranged on the optical axis within the laser resonator. A laser resonator featuring: