JPH0380588A - Etalon of laser equipment - Google Patents

Abstract

PURPOSE:To obtain an etalon of a laser device with improve resistance against laser by enabling both multilayer overcoat and undercoat to be constituted from an optic film thickness which is in even multiples of a specific wavelength. CONSTITUTION:A second SiO2 thin film 6 with an optic film thickness of 1/4 wavelength and an Al2O3 thin film 7 with an optic film thickness of 1/4 wavelength are laminated on a artificial quartz substrate 1 and a multilayer with a total of 25 thin films is formed. Then, for example two layers of a second SiO2 thin film 6 are formed for both overcoat and undercoat of a multilayer film.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an etalon for a laser device in which a high reflection film made of a multilayer film of different types of thin films is formed on a substrate.

[Conventional technology]

Figure 5A is a plan view of the etalon of the narrowband laser device;
Figure B is a side view of Figure 5A, in which an antireflection film (2) and a high reflection film (3) are provided on both sides of a synthetic quartz substrate (1). The high reflection films (3) are optically bonded via a spacer (4) so as to face each other.

Figure 6 is a cross-sectional view showing the film structure of the anti-reflection film (2) [for example, Laser Handbook (Laser Institute, Ohmsha) 19
1982, p. 468], Figure 7 is a diagram showing the spectral reflectance characteristics.The undercoat of the synthetic quartz substrate (1) has a first layer with an optical film thickness (nd) of 172 wavelengths (λ). A SiO2 thin film (5) of 174 wavelengths is applied, and the upper layer is a ^120° thin film (7) with an optical thickness of 174 wavelengths and a MgF2 thin film (8) with an optical thickness of 174 wavelengths.
are applied to each.

FIG. 8 is a cross-sectional view showing the film structure of the high reflection film (3),
On the synthetic quartz substrate (1), ^I20. Thin film (7> and 1
A second 5i02 thin film (6) having an optical thickness of 74 wavelengths is alternately repeated, and the overcoat has an optical thickness of 172 wavelengths.
An alternating multilayer film is formed in which a first SiO□ thin film (5) having an optical thickness equal to the wavelength is applied.

FIG. 9 is a sectional view showing another example of the high reflection film (3) having a different total number of thin films from that in FIG. 8, and FIG. 10 is a diagram showing the spectral reflectance of the high reflection film (3) in FIG. 9. It is.

When the etalon configured as described above is used in a resonator of a laser device, laser beams are incident on the high reflection wA(3) from both the upper and lower directions.

[Problem to be solved by the invention]

In the etalon of a conventional laser device, it is not possible to improve laser resistance by simply applying the first 5if2 thin film (5) with an optical thickness of 172 wavelengths as an overcoat among the high reflection 11g (3) consisting of a multilayer film. The problem was that it was not possible.

The present invention was made to solve this problem, and an object of the present invention is to obtain an etalon for a laser device with high laser resistance.

[Means to solve the problem]

In the etalon of the laser device according to the present invention, both the multilayer overcoat and the undercoat have an optical film thickness that is an even number multiple of 174 wavelengths.

[For production]

In this invention, the optical thickness of both the overcoat and undercoat of the high reflection film is an even number multiple of 1/4 wavelength, so that the electric field intensity does not peak at the boundary between different types of thin films.

〔Example〕

The present invention will be explained in detail below. FIG. 1 is a sectional view showing the film structure of a highly reflective fi(10) showing the first embodiment of the present invention. Second 5in2 thin film (6〉 and 1/
Has an optical film thickness of 4 wavelengths^120. A multilayer film in which the thin films (7) are laminated and the total number of thin films is 25 is formed by an electron beam method. Of the multilayer film, two layers of the second 5ift thin film (6) are formed for both the overcoat and the undercoat.

FIG. 2 shows a second embodiment of the present invention with high reflection [(11
) is a cross-sectional view showing the film structure of a synthetic quartz substrate (1), in which a second Si (+2 thin film (θ) and a ^1203 thin film (7
〉 A multilayer film with a total of 29 thin films is formed by an electron beam method. The second SiO□ thin film (6) in both the overcoat and undercoat of the multilayer film is
N are formed respectively.

Figure 3 shows the high reflection film (10) shown in Figures 1 and 2.
, (11) is a diagram showing the spectral reflectance characteristics of (11), in which (
A) shows the reflectance of the high-reflection film (10), and (b) shows the reflectance of the high-reflection film (10).As can be seen from this figure, the optical film thickness of both the overcoat and undercoat is changed to an even multiple of 174 wavelengths. Even if the total number of films is increased, the reflectance at the center wavelength of the laser is not affected, and the reflection bandwidth is only slightly reduced when the total number of films is increased in terms of optical film thickness of 1/4 wavelength.

A high reflection film (10) of the etalon configured as described above,
(11), of the multilayer film formed on the synthetic quartz substrate (1), both the overcoat and undercoat are 1/2
By stacking the second 5iOz thin film (6) with an optical film thickness of 4 wavelengths in an even number of times, even if the laser is incident on the etalon in both directions, the peak of the electric field distribution in the overcoat and undercoat of the multilayer film will be maintained. It does not appear at the thin film boundary, improving the laser resistance of the etalon.

Note that FIG. 4 shows the electric field distribution when the laser passes through the multilayer film. The laser passes through the multilayer film while being reflected and attenuated at the interface with materials with different refractive indexes.
At this time, it can be seen that the electric field strength is maximum at the position of an odd number multiple of the optical film thickness L/4 wavelength, and is minimum at the position of an even number multiple of the 174 wavelength.9 The table below shows the laser resistance of the high reflection film of the above example. It shows the measured value. Laser resistance is beam area 8
Under the conditions of irradiating one pulse of laser light with a wavelength of 248 nm and a pulse width of 16 ns, 1. J/cm
The power density is increased in steps and is expressed as the power density just before damage occurs with the g-microscope.Therefore, the expression of laser resistance 7 J/cm2 indicates that damage occurs at 8 J/cm2. There is.

Beam surface fl 8nn+" Irradiation wavelength 248 nm Note that in the embodiment, the uppermost layer and the substrate surface layer are made of a material having a thickness that is an even number multiple of the optical film thickness 1/4 wavelength, but other materials may be used. As a high refractive index material,
In the above examples, ^1□03 (aluminum oxide) was used, but other materials such as Sc, 03 (scandium oxide), Zr02 (zirconium oxide), etc.
Any material may be used as long as it has a refractive index of 1.6 or more at 8 nm. Although SiO□ was used as the low refractive index material in the above embodiments, other materials such as Mgl"2.
BaF2. Any material having a refractive index of 1.6 or less at 248 nm, such as CaF2, may be used. Furthermore, although the electron beam evaporation method was used to explain the manufacturing method of the thin film in the above embodiment, other methods such as resistance evaporation method, RF
A stopper method, an ionization vapor deposition method, etc. may also be used.

〔Effect of the invention〕

As explained above, the etalon of the laser device of the present invention has a multilayer overcoat and an undercoat.
Since it is composed of an optical film thickness that is an even number multiple of 74 wavelengths,
The electric field strength does not reach a peak at the boundary between different thin films, resulting in improved laser resistance and significantly longer life.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the structure of a high reflection film of an etalon according to a first embodiment of the invention, FIG. 2 is a sectional view showing a second embodiment of the invention, and FIG. Figure 2 shows the spectral reflectance characteristics of the high-reflection film, and Figure 4 shows the optical multi-NJM.
FIG. 5A is a plan view of the etalon, FIG. 5B is a side view of FIG. 5A, and FIG. 6 is a cross-sectional view showing the structure of a conventional etalon anti-reflection film. Figure 7 is a diagram showing the spectral reflectance of the antireflection film with the structure shown in Figure 6;
9 and 9 are cross-sectional views showing the structure of a conventional example of a high-reflection film, and FIG. 10 shows the spectral reflectance of the high-reflection film having the structure shown in FIG. 9. In the figure, (1) is the synthetic quartz substrate, (5) is the first S
in, thin film, (6> is the second Sin, thin film, (a) is ^
120. The thin films (10) and (11) are highly reflective films. Note that the same gender and the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] In an etalon of a laser device in which a high reflection film made of a multilayer film of different types of thin films is formed on a substrate, the multilayer film has a 1/4 wavelength for both an overcoat at the top of the multilayer film and an undercoat at the bottom of the multilayer film. An etalon for a laser device, characterized in that it has an optical film thickness that is an even number times as large as .