Method and laser system for production of high-resolution laser-induced ...

2. A. Vaidyanathan et al. "Competing Mechanisms in LaserInduced Damage", Damage in Laser Materials: 1979, Bennet et al. (Editors), NBS Special Publication #568 (1979), pp. 457-465.

3. E.W. Van Stryland et al. "Pulse-Width and Focal-Volume Dependence of Laser-Induced Breakdown",Damage in Laser Materials: 1980, Bennet et al. (Editors), NBS Special Publication # 620 (1981), pp. 375-383.

4. J.R. Bettis, "Electron Tunnel Ionization: The Pulse Length and Wavelength Dependence", Laser-Induced Damage in Optical Materials: 1999, Exarhos et al. (Editors), SPIE Vol. 3902 (2000) pp. 302-316.

* cited by examiner

Primary Examiner—Geoffrey S. Evans (57) ABSTRACT

A method and apparatus for production of high-resolution laser-induced damage images by small etch points is based on generation of the initial electron density in the relatively large volume, creation of the breakdown at a small part of the said volume and control of the energy amount enclosed inside the plasma. The method uses two laser radiations: the first has comparatively long pulse width, its energy does not exceed damage threshold value, and it is focused at relatively large focal spot; the second has shorter pulse duration, it is focused at smaller spot and its energy exceeds appropriate threshold value. The system produces laser-induced damage images by joint using of an optical scanner (deflector) and a drive table for movement of article. The system works without interruption of article movement relative to the laser beam and creates image areas with different brightness by modulation of article replacement speed and frequency of scanning.

11 Claims, 2 Drawing Sheets

1

METHOD AND LASER SYSTEM FOR
PRODUCTION OF HIGH-RESOLUTION

LASER-INDUCED DAMAGE IMAGES
INSIDE TRANSPARENT MATERIALS BY

GENERATING SMALL ETCH POINTS 5

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for producing high quality laser-induced damage images in 10 transparent objects.

BACKGROUND OF THE INVENTION

A number of techniques for creating a variety of patterns on the surface and inside of transparent substrates using pulsed laser radiation are well known.

One publication disclosing such techniques is the Russian invention # 321422 to Agadjanov et. al., published on Nov. 16, 1970 (#140454529-33). The invention concerns a 2Q method of manufacturing decorative products inside a transparent material by changing the material structure by laser radiation. As disclosed, by moving a material relative to a focused laser beam, it is possible to create a drawing inside the material. 25

U.S. Pat. No. 4,092,518 to Merard discloses a method for decorating transparent plastic articles. This technique is carried out by directing a pulsed laser beam into the body of an article by successively focusing the laser beam in different regions within the body of the article. The pulse energy 30 and duration is selected based upon the desired extent of the resulting decorative pattern. The effect of the laser is a number of three dimensional "macro-destruction" (fissures in the material of the article) appearing as fanned-out cracks. The pattern of the cracks produced in the article is controlled 35 by changing the depth of the laser beam focus along the length of the article. Preferably, the article is in the form of a cylinder, and the cracks are shaped predominantly as saucer-like formations of different size arranged randomly around the focal point of the optical system guiding a laser 40 beam. The device used to carry out this technique is preferably a multi-mode solid-state, free-running pulse laser used in conjunction with a convergent lens having a focal length from 100 to 200 mm.

U.S. Pat. No. 4,843,207 to Urbanek et al., discloses a 45 method of creating controlled decorations on the surface of a hollow symmetrical transparent article. This technique is preferably carried out on glass. The glass is preconditioned with a coating on the outer surface of the glass being approximately 1.2 mm thick and made of a material having 50 at least 75% absorption of laser radiation. The technique is also carried out using a laser having a wave of length of 0.5 to 2 microns acting upon the external coating through the wall of the cylindrical glass article. The laser beam moves so that it is focused on the surface of the cylinder, and moves 55 about the axis of symmetry of the cylinder to irradiate the aforementioned surface coating. As a result, the irradiated portions of the surface coating go through a phase change and a pattern is formed.

U.S. Pat. No 5,206,496 to Clement et al. discloses a 60 method and apparatus for providing in a transparent material, such as glass or plastic, a mark which is visible to the naked eye or which may be "seen" by optical instruments operating at an appropriate wavelength. The Clement et al. Patent describes a method and apparatus for producing a 65 subsurface marking which is produced in a body such as bottle, by directing into the body a high energy density beam

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and bringing the beam to focus at a location spaced from the surface, so as to cause localized ionization of the material. In the preferred embodiment the apparatus includes a laser as the high energy density beam source. The laser may be a Nd-YAG laser that emits a pulsed beam of laser radiation with a wavelength of 1064 nm. The pulsed beam is incident upon a first mirror that directs the beam through a beam expander and a beam combiner to a second mirror. A second source of laser radiation in the form of a low power He—Ne laser emits a secondary beam of visible laser radiation with a wavelength of 638 m. The secondary beam impinges upon the beam combiner where it is reflected toward the second reflecting surface coincident with the pulsed beam of laser radiation from the Nd-YAG laser. The combined coincident beams are reflected at the reflecting surface via reflecting two other surfaces to a pair of movable mirrors for controlling movement of the beam. The beam then passes through a lens assembly into the body to be marked.

Soviet patent publication 1838163 to P. V. Agrynsky, et. al discloses a process for forming an image in a solid media by processing of the optically transparent solid material by a beam of radiation with changeable energy for creation of the image.

WIPO Patent Document No. 96/30219 to Lebedev et al. discloses a technology for creating two- or threedimensional images inside a polymer material using penetrating electromagnetic radiation. The technology can be used for marking and for producing decorative articles and souvenirs. Specifically, laser radiation is used as the penetrating radiation, and carbonizing polymers are used as the polymer material. By these means, it is possible to produce both black and half-tone images in the articles.

U.S. Pat. No. 5,575,936 to Goldfarb discloses a process and apparatus where a focused laser beam causes local destruction within a solid article, without effecting the surface thereof. The apparatus for etching an image within a solid article includes a laser focused to a focal point within the article. The position of the article with respect to the focal point is varied. Control means, coupled to the laser, and positioning means are provided for firing the laser so that a local disruption occurs within the article to form the image within the article.

U.S. Pat. No. 5,637,244 to Erokhin discloses a technique which depends on a particular optical system including a diffraction limited Q -switched laser (preferably a solid-state single-mode TEM00) aimed into a defocusing lens having a variable focal length to control the light impinging on a subsequent focusing lens that refocuses the laser beam onto the transparent article being etched. The laser power level, operation of the defocusing lens, and the movement of the transparent article being etched are all controlled by a computer. The computer operates to reproduce a preprogrammed three-dimensional image inside the transparent article being etched. In the computer memory, the image is presented as arrays of picture elements on various parallel planes. The optical system is controlled to reproduce the stored arrays of picture elements inside the transparent material. A method for forming a predetermined half-tone image is disclosed. Accordance to the method, microdestructions of a first size are created to form a first portion of the image and microdestruction of a second size different from the first size are created to form a second portion of the image. Different sizes of microdestructions are created by changing the laser beam focusing sharpness and the radiation power thereof before each shot.

U.S. Pat. No. 5,886,318 to A. Vasiliev and B. Goldfarb discloses a method for laser-assisted image formation in