JPS6228852B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for evaluating optical damage to optical elements such as mirrors and windows used in lasers.

Conventionally, there has been a device of this type as shown in FIG. In this figure, 1 is a He-Ne laser, 2 is an optical element such as a mirror or window, and 3 is the He-Ne laser mentioned above.
- This is a photodetector that detects scattered light generated when Ne laser light is focused on the optical element 2.

Although the conventional light scattering evaluation apparatus is constructed as described above, it has the following drawbacks.

In other words, conventional equipment detects changes in surface conditions due to optical damage based on changes in light scattering intensity, but the method of detection is to read the information recorded by a photodetector, an amplifier, and a recorder. be. In this method, the response speed of the measurement system is slow and it is only possible to follow large changes when damage has definitely occurred. On the other hand, in order to investigate the cause of optical damage, it is important to know the stages of damage occurrence, progression, and destruction, but with conventional methods, the time course of the above three stages is very fast, and observation is difficult. There was a drawback that I couldn't do it. Second
The figure shows a schematic diagram of the change in damage over time.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and uses a laser beam separate from the laser beam of the laser device for optical damage evaluation. By providing a photodetector for irradiating the incident point of the separate laser beam and observing the scattered light from the irradiation surface, and providing a high-speed response recording device for recording the signal from this photodetector at high speed,
The purpose of this study is to provide a device that can capture temporal changes in photodamage and have a significant effect on elucidating the mechanism of photodamage.

Next, before going into the description of the embodiments, the meaning of "optical damage to optical elements" mentioned in this invention will be explained.

First of all, "optical element" in this invention refers to a high-output laser for industrial processing (welding, fusing, trimming, surface treatment, etc.) or a high-output laser for medical use, which has a low output but has a high output density (by narrowing down the laser beam). This refers to resonator mirrors, beam splitters, condensing lenses, etc. in laser equipment that has a wavelength of W/cm ² ), and in the case of lenses, it has a transmittance with as little absorption as possible for the wavelength of the laser light normally used. A material with a high reflectance is selected, while a dielectric multilayer film is used for the reflective mirror to make the reflectance as high as possible. And "optical damage" to such elements refers to the fact that when the laser light output used is powerful, clouding occurs within the surface of these optical elements, despite the selection of materials with low absorption or high reflectivity. , cracks, cracks, etc. may occur.
This means that it becomes useless as an optical element. The cause of damage is said to be thermal destruction of the material due to absorption of laser light or strong electric field destruction due to the electric field of light in the case of high power density.
In any case, these optical elements are extremely expensive in terms of materials and processing, and once damage occurs, the laser system will stop completely, so damage becomes a big problem as laser light output increases. ing.

An embodiment of the present invention will be described below with reference to the drawings.

In Figure 3, 1 is He for light scattering measurement.
-Ne laser, 6 is a He-Ne laser beam for optical damage evaluation, 2 is an optical element, 7 is the reflected light of the He-Ne laser beam 6, 4 is a laser beam that induces optical damage, 5 is the optical element 2 8 is a lens for condensing the scattered light; 3 is a photodetector for detecting the scattered light; 9 is a broadband amplifier with good high-speed tracking that receives the signal from the photodetector; 10 is a wideband amplifier that receives the signal from the photodetector; A fast transient phenomenon recorder, 11 is a recorder.

Next, the operation will be explained. The beam 6 from the He--Ne laser 1 is irradiated to the optical element 2 at the irradiation position of the laser beam 4 that induces damage, and becomes reflected light 7. Changes due to damage to the surface of the optical element 2 result in changes in the intensity of the scattered light, which reaches the photodetector 3 via the condenser lens 8 . Changes in the scattered light are converted into electrical signals by the photodetector 3, which are guided to the transient phenomenon recorder 10 via the broadband amplifier 9, and the changes from the initial stage of damage to progress and destruction are recorded at high speed.

In addition, in the above example, He--Ne was used as the laser.
This invention uses laser 1, but this invention
The laser is not limited to the He--Ne laser 1, but any laser having an oscillation line in a wavelength range in which a photoelectron amplifier tube can be used may be used. Although the optical axes of the laser beam 4 and the beam 6 from the He--Ne laser 1 are shown not to be coaxial in FIG. 3, they can be made co-axial by appropriately using a beam splitter. The laser beam from the Ne laser 1 may also be vertically incident on the optical element 2.

As described above, according to the present invention, it is possible to irradiate a laser beam that causes optical damage while applying a separate laser beam to the irradiated area and record changes in scattered light in that area at high speed in real time. It is possible to accurately observe the process of damage occurrence, progression, and destruction.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram showing a conventional optical damage evaluation device.
FIG. 2 is a schematic diagram of temporal changes in scattered light intensity indicating surface changes due to damage, and FIG. 3 is a schematic diagram of the configuration of an optical damage evaluation apparatus showing an embodiment of the present invention. 1 is a He-Ne laser, 2 is an optical element, 3 is a photodetector, 4 is a laser beam that induces optical damage, 5 is a transmitted beam, 6 is a He-Ne laser beam, 7 is a He-Ne laser beam reflected light , 8 is a condensing lens for scattered light, 9 is a broadband amplifier, 10 is a transient phenomenon recorder, and 11 is a recorder. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] 1. Means for injecting a laser beam for damage evaluation, which is different from the laser beam, into the irradiation position of the laser beam of the test sample that is irradiated with the laser beam that causes photodamage, and a means for evaluating the damage generated from the irradiation position. A laser-induced damage evaluation device consisting of a photodetector that observes scattered laser light and a transient phenomenon recording device that records signals from the photodetector at high speed.