JPH01225186A - Narrow band laser - Google Patents

Abstract

PURPOSE:To suppress a wavelength distribution in a laser beam and to improve the quality of a narrow band laser by providing an aperture out of an optical resonator, and so reducing the diameter of the beam to be radiated from the resonator to an effective diameter falling in an allowable range of the wavelength of the beam. CONSTITUTION:An aperture 6 is provided out of an optical resonator, and the diameter of a laser beam 5 to be radiated from the resonator is reduced to an effective diameter falling in an allowable range of the wavelength of the beam 5. That is, an unallowable part of the wavelength distribution in the beam 5 generated due to the manufacturing accuracy or a thermal strain of an etalon 4 is suppressed by the aperture 6. Thus, the wavelength distribution in the beam is reduced so that the wavelength shift falls within the allowable range of the whole beam 5.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a narrowband laser, and particularly to suppression of the wavelength distribution of the laser beam.

[Prior art] Figure 3 shows, for example, the magazine rOPTIcs LETTER5J.
1 ('77) 199, in which (1) is the laser medium, (
2) is a total reflection mirror, and (3) is a partial reflection mirror, and these mirrors (2) (:l) are arranged opposite to each other with the laser medium (1) in between. (4) is an etalon, (5) is a laser beam, and (7) is a spacer.

Next, the operation will be explained. When an optical resonator consisting of a total reflection mirror (2) and a partial reflection mirror (3) is constructed with a laser medium (1) in between, the light is amplified as it travels back and forth within this optical resonator and becomes a laser beam (5). emits. By the way, some types of lasers having such a configuration, such as semiconductor lasers, alexandrite lasers, dye lasers, excimer lasers, etc., have a wide wavelength range that can be amplified, and therefore the wavelength width of the laser beam is also wide. Therefore, by inserting a spectroscopic element such as an etalon, grating, or prism into the optical resonator of this type of laser, light can be selected and a laser beam with a narrow wavelength width can be obtained.

Of these, etalons are very commonly used elements because of their low loss and high tolerance to vibration.

An etalon is an interferometer with two highly precisely polished reflective surfaces, allowing only a range of wavelengths to pass, determined by the optical distance between the two reflective surfaces.

The etalon shown in Figure 3 is an air-gap type of etalon, and after polishing two substrates and applying a reflective coating, the reflective surfaces of each are glued together with a spacer (8) in between. This is what I did. The parallelism of the gap that occurs at this time allows only a sufficiently small error in the plane through which the laser beam passes, even compared to the wavelength of the laser beam.Therefore, several spacers are polished to the same thickness as possible. Moreover, it is necessary to attach the spacers as far apart as possible.

[Problem to be solved by the invention] Since the conventional narrowband laser is configured as described above, the distance between the spacers is wide, and therefore the etalon has a size several times the size of the laser beam. was using. By the way, as the laser output increases, the etalon generates heat and has a temperature distribution. Then, the etalon substrate also swells accordingly, resulting in a wavelength shift and an oscillation wavelength of 4i within the laser beam. The former shows the maximum temperature change, and the latter shows the change corresponding to the temperature gradient. By the way, the former can be corrected by tilting the etalon, changing the length of the gap, or changing the refractive index of the gas in the gap, but the latter can be corrected because it is difficult to cool from the center of the etalon. It's not easy. Moreover, in the conventional device, since the beam diameter is small compared to the etalon diameter, the temperature gradient is large, and therefore the wavelength distribution within the laser beam is also significant.

This invention has been made to solve the above-mentioned problems, and is designed to reduce the wavelength distribution within a laser beam so that the wavelength shift is within an allowable range over the entire laser beam.

[Means for Solving the Problems] The narrowband laser according to the present invention is provided with an aperture outside the optical resonator so that the diameter of the laser beam emitted from the optical resonator can be adjusted so that the wavelength of the laser beam is within an allowable range. It is narrowed down to the effective diameter.

[Function] The band-narrowing laser according to the present invention uses an aperture to block portions that are unacceptable due to etalon manufacturing accuracy or wavelength distribution within the laser beam caused by thermal strain.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings. 1st
4, (1) is a laser medium, (2) is a total reflection mirror,
(3) is a partial reflecting mirror, (4) is an etalon, (5) is a laser beam, (6) is an aperture, and (7) is an etalon spacer.

Next, the operation will be explained. Similar to the conventional example, in some types of lasers, the laser wavelength band can be narrowed by inserting a spectroscopic element into the optical resonator. By the way, when examining the wavelength at each point within a laser beam, a wavelength distribution always occurs.

FIG. 2 shows an example of this. The horizontal axis shows the radial position, and the vertical axis shows the wavelength. First, the broken line A is the wavelength distribution immediately after excavation, which is mainly caused by the fact that the reflective surfaces of the two substrates of the etalon are not kept in a straight line. Also,
In general, wavelength distribution has a tolerance range for different wavelengths.

For example, when performing precision processing using this laser beam,
If there is a wavelength in, chromatic aberration will occur in the processing optical system, and the laser beam will become blurred. This allowable range is indicated by a dashed line B. As is clear from the figure, if the diameter of the laser beam is increased, it is expected that the permissible range will be exceeded even immediately after oscillation.

On the other hand, the solid line C is the wavelength distribution during steady operation. During steady operation, the etalon absorbs the laser beam and thermal distortion occurs, resulting in such an extreme wavelength distribution.

This distribution is approximately proportional to the temperature distribution.

However, in this figure, the overall wavelength shift is subtracted. As can be seen from the figure, the effective diameter r, where the wavelength is within the allowable range, is small relative to the laser beam diameter.This effective diameter is uniquely determined by the laser output and the absorption rate of the etalon, so All you have to do is conduct a test in advance to find out the wavelength distribution, and use an aperture to block out the portions where the wavelength exceeds the allowable range.

By the way, regarding the location where the aperture is placed, if it is placed inside an optical resonator, the laser beam diameter will become smaller, so there will be an increased difference from the etalon diameter, and the temperature distribution will become significant and the wavelength distribution will also become extreme.

Therefore, it is better to place it outside the optical resonator and cut the emitted light. In this case, the cut light serves to warm the etalon and smooth out the temperature distribution. For the same reason,
By making the etalon smaller and reducing the ratio of the etalon diameter to the beam diameter, the temperature distribution can be made more gentle. However, in this case, the distance between the spacers becomes smaller and the parallelism deteriorates, so the slope of the wavelength distribution shown by the broken line A in Figure 2 becomes steeper, so the aperture exceeds the effective diameter. must be cut by.

[Effects of the Invention] As described above, according to the present invention, an aperture is provided outside the optical resonator of a narrowband laser, and the diameter of the laser beam emitted from the optical resonator can be adjusted so that the wavelength of the laser beam is within an allowable range. Since the diameter is narrowed to the effective diameter, the wavelength distribution within the laser beam is suppressed, which has the effect of improving beam quality.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a narrowband laser according to an embodiment of the present invention, FIG. 2 is an explanatory diagram illustrating the wavelength distribution of the narrowband laser, and FIG. 3 is a conventional narrowband laser. FIG. (1)--Laser medium, (2)--Total reflection mirror, (3
) - Partial reflector, (4) - Etalon, (5)
. . . Laser beam, (6) . . . Aperture In the drawings, the same reference numerals indicate the same or corresponding parts. Agent Masuo Oiwa

Claims (1)

[Claims] An optical resonator constituted by mirrors arranged facing each other with a laser medium in between, an etalon provided within the optical resonator to select the oscillation wavelength, and an etalon provided outside the optical resonator to emit light from the optical resonator. A band-narrowing laser includes an aperture that narrows down the diameter of a laser beam to an effective diameter within an allowable range of the wavelength of the laser beam.