JPH1031106A - Laser mirror for multiwavelength - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a laser mirror having a wider high reflection band than a high reflection band of a normal mirror although the number of layers of the new mirror is almost the same as that of a normal laser mirror and the same material is used for films, by alternately depositing layers in such a manner that these layers include layers having a specified range of optical film thickness and that other layers have specified optical film thickness. SOLUTION: This mirror is produced by alternately depositing high refractive index layers 2 and low refractive index layers 3 on an optical substrate. When λis the designed center wavelength, these alternately deposited layers include at least one layer having the optical film thickness between >=0 and <=0.1λ or between >=0.35λ and <=0.65λ and other layers are formed to have about 0.25λ optical film thickness. For example, the structure of a multiwavelength laser mirror is expressed by 6(HL).2H.6(LH), in which the high refractive index layer 2 is composed of TiO2 and the low refractive index layer 3 is composed of SiO2 . In 25 layers of the laser mirror, the 13th layer has λ/2 optical film thickness while other layers have λ/4 optical film thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a multi-wavelength laser mirror used in a laser optical system.

[0002]

2. Description of the Related Art As a mirror that reflects visible light, there are a mirror made of a metal thin film and a mirror made of a dielectric multilayer film.
Among them, a mirror composed of a dielectric multilayer film that efficiently reflects light of a single wavelength such as a laser is called a laser mirror, and is often used in a laser optical system.

[0003] The basic film configuration of a laser mirror consists of a high refractive index layer (hereinafter referred to as H) having an optical film thickness of λ / 4 on a substrate,
HLHLH are alternate combinations of low refractive index layers (hereinafter referred to as L) having an optical film thickness of λ / 4. The reflectance is adjusted by the number of repetitions of the alternate combination, and a high reflectance may be obtained by increasing the number of repetitions.

Since the high reflection band is theoretically defined by the refractive index difference between the high refractive index layer and the low refractive index layer, in order to obtain a wide reflection band, it is necessary to select a film material having a large refractive index difference. I just need.

[0005]

However, when high reflection is required at several wavelengths at the same time, even if the refractive index difference is maximized by selecting a film material and the high reflection band is widened, the required wavelength is not increased. There are times when it doesn't work. In addition, film materials that sufficiently satisfy the requirements for physical properties such as laser proof stress and the like and film quality and have a large difference in refractive index are limited.

Further, when the required wavelength is barely contained at both ends of the high reflection band of a normal laser mirror, the high reflection band fluctuates due to a manufacturing error of the film, and the required wavelength deviates from the high reflection band. The problem of disappearing occurs. In such a case, the method of overlapping the laser mirrors for different wavelengths to increase the reflection band is used, but the method of overlapping the laser mirrors for different wavelengths to increase the reflection band increases the number of layers significantly. Inevitably, this causes manufacturing disadvantages, such as increased costs, and optical disadvantages, such as increased scattering and reduced laser tolerance.

Accordingly, the present invention provides a multi-wavelength laser having a high reflection band wider than that of a normal laser mirror by using the same film material with the same number of film layers as that of a normal laser mirror. It is intended to provide a laser mirror.

[0008]

SUMMARY OF THE INVENTION The present invention firstly provides a multi-wavelength laser mirror in which alternating layers of a high refractive index layer and a low refractive index layer are laminated on an optical substrate, and has a design center wavelength. λ
Wherein the optical thickness of the alternating layers is 0 or more and 0.1λ or more.
Or at least one layer having a thickness of not less than 0.35λ and not more than 0.65λ, and the other layer has an optical thickness of about 0.25λ.
A multi-wavelength laser mirror (Claim 1).

The present invention also relates to a second aspect of the present invention in which the number of layers having an optical film thickness of 0 to 0.1 λ or 0.35 λ to 0.65 λ is counted from the substrate other than the first layer or the final layer. A multi-wavelength laser mirror according to claim 1 (claim 2) "is provided.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a laser mirror according to an embodiment of the present invention will be described with reference to the drawings. 5
A laser mirror having a high reflectance of 99% or more at 60 nm and 720 nm will be described as an example.

FIG. 1 shows a multi-wavelength laser mirror according to the first embodiment. The film configuration of the multi-wavelength laser mirror according to the first embodiment of the present invention is 6 (H
L) ・ 2H ・ 6 (LH), and the high refractive index layer 2
It consists iO _2, the low refractive index layer 3 is made of SiO _2. 25
The optical film thickness of the thirteenth layer of the laser mirror of the layer is λ /
2, and the optical thickness of the other layers is λ / 4.

The design center wavelength λ is 633 nm. Optically polished quartz glass, silicon, BK7 as substrate 1
And the like, but are not particularly limited. High refractive index layer 2
As zirconium oxide (ZrO ₂ ), titanium oxide (TiO ₂ ), tantalum oxide (Ta ₂ O ₅ ), niobium oxide (Nb ₂ O ₅ ), hafnium oxide (HfO ₂ ), cerium oxide (CeO ₂ ) or the like And mixtures thereof.

As the low refractive index layer 3, aluminum oxide
(Al_TwoO_Three), Silicon oxide (SiO _Two), Magnesium fluoride
Nesium (MgF_Two), Germanium oxide (GeO)_Two),
Aluminum fluoride (AlF_Three) And the like. Departure
Multi-wavelength laser mirror according to first embodiment according to the present invention
FIG. 2 shows the spectral reflectance characteristics of.

High reflectivity is exhibited at 560 nm and 720 nm, and the high reflection band is about -15 nm around 560 nm.
nm to +70 nm, about -80 n around 720 nm
m to +20 nm, and sufficiently exhibit high reflectance at 560 nm and 720 nm even if the high reflection band fluctuates due to some manufacturing errors. Also, the ripple is only at the center of the high reflection band, and this position varies greatly due to the manufacturing error of the λ / 2 film thickness of the thirteenth layer even if there is a slight manufacturing error. There is no. Comparative Example The film configuration of the multi-wavelength laser mirror according to Comparative Example 1 was 12 (HL) · H, and the high refractive index layer was TiO.
₂ and the low refractive index layer is made of SiO ₂ .

FIG. 3 shows the spectral reflectance characteristics of the multi-wavelength laser mirror according to Comparative Example 1. 560nm and 720n
Although high reflection of 99% or more can be ensured in m, the high reflection band is about -5 nm and 720 nm for 560 nm.
If the spectral characteristics are shifted due to a manufacturing error, one of the wavelengths is out of the high reflection band, and the requirement is not satisfied.

The film configuration of the multi-wavelength laser mirror according to Comparative Example 2 is such that each layer has an optical thickness other than λ / 4 (each layer is optimized by a thin film design), and a high refractive index layer and a low refractive index layer. There are 25 alternating layers of layers. High refractive index layer is Ti
O ₂ , and the low refractive index layer is made of SiO ₂ . FIG. 4 shows the spectral reflectance characteristics of the multi-wavelength laser mirror according to Comparative Example 2.

Although high reflection of 99% or more can be ensured at 560 nm and 720 nm, there are a large number of recesses in the reflectance of a high reflection band called a ripple, and the position and size of the ripple are shifted due to manufacturing errors. Considering
It may not be possible to satisfy the request. FIG. 5 shows a multi-wavelength laser mirror according to the second embodiment.

The film configuration of the multi-wavelength laser mirror according to the second embodiment of the present invention is 4 (HL) .2H.3.
(LH) · L · 2H · 4 (LH), where the high refractive index layer 2 is made of TiO ₂ and the low refractive index layer 3 is made of SiO ₂ . The optical thickness of the ninth and seventeenth layers of the 25-layer laser mirror is λ / 2, and the optical thicknesses of the other layers are λ / 4.

FIG. 6 shows the spectral reflectance characteristics of the multi-wavelength laser mirror according to the second embodiment of the present invention. The ripple at the center is larger, but at 560 nm and 720
high reflectivity in nm, high reflection band is 560 nm
From about -20 nm to +50 nm centering on the center, and from about -70 nm to +40 nm centering on the 720 nm.
It shows high reflectance at 0 nm and 720 nm.

[0020]

As described above, the multi-wavelength laser mirror according to the present invention sacrifices the reflectance for a part of the wavelength. A high reflection band wider than the high reflection band of a normal laser mirror could be achieved by using the same film material with the same number of film layers as the mirror.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a mirror for a multi-wavelength laser according to a first embodiment.

FIG. 2 shows a spectral reflectance characteristic of the multi-wavelength laser mirror according to the first embodiment.

FIG. 3 is a spectral reflectance characteristic of a multi-wavelength laser mirror according to Comparative Example 1.

FIG. 4 shows a spectral reflectance characteristic of a multi-wavelength laser mirror according to Comparative Example 2.

FIG. 5 is a schematic sectional view of a multi-wavelength laser mirror according to a second embodiment.

FIG. 6 shows a spectral reflectance characteristic of the multi-wavelength laser mirror according to the second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... High refractive index layer 3 ... Low refractive index layer

Claims (2)

[Claims] 1. A multi-wavelength laser mirror comprising an alternating layer of a high-refractive-index layer and a low-refractive-index layer laminated on an optical substrate, wherein a design center wavelength is λ, and The film thickness is from 0 to 0.1λ or from 0.35λ to 0.65λ.
A multi-wavelength laser mirror comprising at least one of the following layers, and the other layer has an optical thickness of about 0.25λ. 2. The method according to claim 1, wherein the layer having the optical film thickness of 0 to 0.1λ or 0.35λ to 0.65λ is provided in addition to the first layer or the last layer, counting from the substrate side. The multi-wavelength laser mirror according to claim 1.