JPS6378102A - Reflection preventing film for tellurium dioxide - Google Patents

Abstract

PURPOSE:To obtain the titled film having high light resisting power against laser ray, without giving change to optical characteristics by forming an aluminum oxide film and a silicon dioxide film in this order on the surface of a tellurium dioxide substrate. CONSTITUTION:The titled film is formed by laminating the aluminum oxide (Al2O3) film and the silicon dioxide (SiO2) film in this order on at least one surface of the tellurium dioxide (TeO2) substrate which is polished for an acoustooptic element. Thus, the TeO2 substrate of the acoustooptic element does not almost change the optical characteristics, and reflection loss is small, thereby taking out the laser ray with good efficiency, even in the case that the polarization state of the laser ray incident upon said TeO2 substrate is either ordinary ray incidence or extraordinary ray incidence. And, the titled film can be proof against the continuous irradiation of the laser ray.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an antireflection film for tellurium dioxide, which is a material for acousto-optic elements (light modulation elements, optical deflection elements, acousto-optic filters, etc.) that utilize the acousto-optic effect. It is something.

Recently, tellurium dioxide crystals (hereinafter referred to as TeO2) have been used in acousto-optic elements that utilize the acousto-optic effect.

In recent years, laser light sources in the visible range have tended to have shorter wavelengths and higher outputs. Te has a short ultraviolet absorption edge of 330 nm.
02 also has a durability against laser light of 100 w/mm.
It has two major features. Therefore, Ar ion L/
- laser (wavelength 488 mm) and He -Cd laser (wavelength 4
42 mm) has been widely used as an acousto-optic element for optical modulators and optical deflectors. Furthermore, it has been used as an acousto-optic filter to obtain arbitrary monochromatic light from a white light source.

However, TeO2 has optical anisotropy and is divided into ordinary rays and extraordinary rays depending on whether the plane of polarization of the light incident on the crystal orientation (001) axis is perpendicular or horizontal. Furthermore, at this time, TeO2 has an ordinary ray refractive index (hereinafter referred to as nQ) for ordinary rays, and an extraordinary ray refractive index (hereinafter referred to as n6) for extraordinary rays. It has a refractive index.

In other words, the refractive index of Te 02 changes from no to ne depending on the polarization plane of the incident light, and the spectral optical characteristics change greatly depending on whether the incident light is ordinary light, extraordinary light, or random light.

TeO2 has come to be widely used in optical modulators, deflectors, and acousto-optic filters, and is used for reflection purposes to improve its transmittance and to prevent spectral optical characteristics from changing depending on the polarization plane of incident light, such as ordinary light or extraordinary light. Demand for protective films has increased.

Conventionally, magnesium fluoride (hereinafter referred to as MgF2) has been used as an antireflection film for TeO2 because it is optically transparent over a wide range from the infrared region to the ultraviolet region and is easy to manufacture as an antireflection film.

Problems to be Solved by the Invention However, the refractive index of TeO2 changes from no to n6 depending on the polarization plane of the incident light (for example, the wavelength of 633
(n = 2.26, rle = 2.41), therefore, a MgF2 film with a refractive index of 1.38 has problems such as its optical properties changing greatly depending on the polarization plane of the incident light. was not improved. For example, MgF2
A He-Ne laser (e length 632.8 nm), which is a typical visible light laser, is applied to a TeO2 substrate on which an antireflection film is formed.
When the light of This caused a large change in reflection loss.

Furthermore, in recent years, the wavelength of laser light has progressed to become shorter, and Ar lasers (wavelength: 488 nm), He-Cd lasers (wavelength: 442 nm), and the like have come to be widely used as light sources. Along with this, n, ) and ne ( of TeO2
For example, at 442 nm no = 2.38, n6 = 2
．． 55) As shown in Fig. 8, when a He-Cd laser beam with a wavelength of 442 nm is incident on a Te 02 substrate on which an anti-reflection film of MgF2 film is formed,
The reflection losses on one side due to the incidence of ordinary rays (line n□ in the figure) and extraordinary rays (line n6 in the figure) are 1.2% and 2.1%, respectively, as shown by the arrows in the figure. Wavelength 632.8
Compared to the case of nm light, the change in optical characteristics when ordinary rays and extraordinary rays are incident is about 1%, which is even larger. Further, the value of reflection loss also increases approximately twice compared to when the He--Ne laser beam is incident. Furthermore, as the laser equipment used also tends to have higher output year by year, the hygroscopicity of the MgF2 film increases the amount of heat absorbed during laser beam irradiation, which deteriorates the MgF2 film in the irradiated area and increases the transmittance. There was a problem in that it decreased.

The present invention solves the above problems, and is an anti-reflection film for tellurium dioxide that has almost no change in optical properties even if the polarization plane of the incident laser light changes, and is durable against laser light irradiation. The purpose is to provide a membrane.

Means for Solving the Problems The present invention uses polished TeO as an acousto-optic element.
The above object is achieved by overlappingly forming an aluminum oxide (hereinafter referred to as Az2O3) film and then a silicon dioxide (hereinafter referred to as 5i02) film on at least one surface of two substrates.

Function The present invention provides an acousto-optic element TeO2 with the above configuration.
Even when the polarization state of light such as a laser beam that enters the substrate becomes ordinary or extraordinary light, there is almost no change in the optical properties, and the laser light can be efficiently extracted with low reflection loss. Furthermore, it is designed to withstand continuous irradiation with laser light.

Examples Below are examples of Ar ion laser light (wavelength 488 nm) of the present invention.
An example will be described with reference to the drawings.

FIG. 1 is a structural diagram of a two-layer anti-reflection coating formed on one surface of a TeO2 substrate according to the present invention. 3 in the figure has a wavelength of 488 nm and n□ of 2.33, both sides of which are optically polished.
It is a Te 02 substrate with ne of 2.49.

l is AI with a refractive index n1 of 163! 203 film and has an optical thickness n1d1=77.27 nm.

2 is a 5i02 film having a refractive index n2 of 1.45 and an optical thickness n2d2 = 56.65 nm. Each of the above optical film thicknesses can be determined using the Munchar relational formula (Mouchar t;A
pplied 0ptics VoL 16. No,
10 P2722), and the thickness of the third layer was determined to be zero.

FIG. 2 shows the wavelength dependence of an antireflection film formed on a Te 02 substrate for an Ar ion laser (λ=488 nm) according to this example. The line indicated by the arrow n□ in the figure is
This is the case when ordinary rays are incident on the TeO2 substrate, and the line indicated by arrow n6 shows the wavelength dependence of the reflectance when extraordinary rays are incident. The reflectance at a wavelength of 488 nm is 0.1% or less, and even if the refractive index of the TeO2 substrate changes from n□ to n6, it remains at the center wavelength 488
As shown by the arrow in the figure, the reflectance in nm did not change so much that the two overlapped with each other, and good results were obtained.

Figures 3 and 4 show the first layer of Al2O5 film 1,
The wavelength dependence of the reflectance is shown when the optical thickness n1di of the second layer 5i02 film 2 is increased or decreased by 10% with respect to the set value.

FIG. 3 shows the optical thickness of the second layer 5i02 film 2 of 56.
The first layer A# has a thickness of 65 nm and is in close contact with the TeO2 substrate 3.
When the optical thickness of the zOs film 1 is changed, A120
3 The optical thickness of film 1 is 69.54 nm - 85,00
In the nm range, the reflectance at a wavelength of 488 nm is 0.
It was a good 17%.

The fourth factor is the AJL of the first layer that is in close contact with the Te 02 substrate 3.
'203 film 1 has an optical thickness of 77.27 nm, and Al
When the optical thickness of the second layer 5i02 film 2 formed on the t203 film l is changed, the optical thickness of the 5i02 film 2 is in the range of 50.98 nm to 62.31 nm at a wavelength of 488 nm. Good results were obtained with a reflectance of about 0.1%.

FIG. 5 shows the wavelength dependence of the reflectance when the optical thickness of the Al2O3 film 1.5i02 film 2 is simultaneously increased by 10% and decreased by 10%. Since the reflectance at a wavelength of 488 nm is about 0.46%, the total reflectance in the case of a double-sided anti-reflection coating is about 0.9%, which is the practical limit.

As is clear from this figure, the optical thickness of the antireflection film for Te 02 against Ar ion laser light according to this example is 69.54 nm to 8 nm for the first layer AJ203 film l.
5.00 nm, second layer 5i02 film 2 is 50.98n
The range is preferably from m to 62.31 nm.

FIG. 6 shows a second embodiment of the present invention, in which the first layer A
By setting the optical thickness of the 12O3 film 1 to 73.63 nm, the optical thickness of the second layer 5i02 film 2 to 53.98 nm, and setting the center wavelength to 465 nm, the optical thickness of the Ar ion laser (λ The wavelength dependence of the reflectance when an antireflection effect is provided to both laser beams of a He-Cd laser (λ=488 nm) and a He-Cd laser (λ=442 nm) is shown. As is clear from this figure, the wavelengths are 442 nm and 488 nm.
The reflectance in each case is good at about 0.15%.

Furthermore, there is almost no change in reflectance whether the incident laser beam is an ordinary ray (line n□ in the figure) or an extraordinary ray (line n6 in the figure), and there is a sufficient reflection prevention effect for both laser beams. A preventive film was easily formed.

Figure 7 shows a TeO2 substrate 3 (8mm x 10mm x 2mm
t) on (=, anti-reflection film according to this example (Al2O3/
5iO2) formed on both sides and conventional technology MgF2
This figure shows the results of a light resistance test using a He-Cd laser beam of a sample with a film formed on both sides.

The output of the He-Cdv-za is 37 mW, the beam diameter of the laser beam is focused to 26 μm using a lens, and the power density is 7 mW.
0 w/mz12 (-) and shows the change in transmittance over time when the sample is continuously irradiated.As is clear from this figure, the (A#Ox/5iO2) film is Even after irradiation for 12 hours or more, the transmittance changes over time.
The change in transmittance over time can be reduced to about 1/7 of the 17% change in the MgF2 film, which is about 2.5%.

Effects of the Invention As described above, the present invention provides an antireflection film for Te 02 formed by stacking an A#205 film and then a 5i02 film on at least one surface of a TeO2 substrate.
2. The plane of polarization of the light source such as a laser beam that enters the substrate is the ordinary ray,
The anti-reflection coating has a great effect, with almost no change in optical properties even when the light changes to extraordinary rays or randomly polarized light, and which has high light resistance even to laser light.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view for explaining an antireflection film for TeO2 in an example of the present invention, and FIG. 2 shows an (A#203/5iO2) film formed on one surface of a TeO2 substrate, and Figure 3 shows the wavelength dependence of reflectance when an extraordinary ray is incident. Figure 3 shows the wavelength dependence of reflectance when the optical thickness of the first layer A4203 film is increased or decreased by 10% from the set value. Figure 4 shows the wavelength dependence of reflectance when the optical thickness of the second layer 5i02 film is increased or decreased by 10% from the set value, and Figure 5 shows the wavelength dependence of the reflectance when the optical thickness of the second layer 5i02 film is increased or decreased by 10% from the set value. Figure 6 shows reflectance dependence when increased or decreased by 10%.
The figure shows the wavelength dependence of the reflectance for Ar ion laser light and He-Cd laser light in the present invention. Figure 7 shows the reflection prevention (A1
203/S i 02 ) film and the prior art MgF2 film using He-Cd laser light. It is a diagram showing the wavelength dependence of reflectance when a MgFz film is formed and ordinary rays and extraordinary rays are incident. 1 = AJ205 film, 2-8iO2 film, 3-TeO
2 boards. Figure 1 Figure 2 Figure 2 (nyy + Ji Figure 3 Growth (tryn) Figure 4 Destruction (ka m2 Figure 5 Wolf (Layer) Figure 6 Figure 7 Time (h Oboros) )

Claims (2)

[Claims] (1) An antireflection film for tellurium dioxide, characterized in that an aluminum oxide film and a silicon dioxide film are formed in this order on at least one surface of a tellurium dioxide substrate. (2) The optical thickness values of the first layer of aluminum oxide film and the second layer of silicon dioxide are 69.54 nm to 8.
The antireflection film for tellurium dioxide according to claim 1, which has a wavelength of 5.00 nm and 50.98 nm to 62.31 nm.