3 4
length defocusing lens is interposed between the pulsed laser Another peculiar feature of the selected laser type resides
and the focusing lens, said defocusing lens being adapted for in utilizing utmost possibilities of sharp radiation beam
changing the occupancy of the actual aperture of the focus- focusing, which is schematically represented in FIG. 2.
ing lens. The mechanical driving means for mutual displace- A sharp laser radiation focusing necessary for normal
ment of the transparent material and the laser beam is shaped 5 operation of the apparatus is carried out as follows,
as a single-axis and two-axis motion mechanism. The laser radiation beam 3 having a diameter d is incident
Adjusting microdestxuctions characteristics it is possible Up0n the defocusing lens 2 and emerges therefrom in a
now to produce three or two-dimensional images of a pre-set diverging form to get into the aperture of the focussing lens
pattern in transparent materials having various shapes and 4 and having a diameter D which is found from the formula
mechanical features, e.g. hardness. 10
D=d(L+f)/f,
BRIEF DESCRIPTION OF THE DRAWINGS
where L is the distance between the lenses
The present invention will be more apparent from the f is me focal length of the defocusing lens
following description of more specific exemplary embodi- a case 0f aberrationless focusing by the lens 4 the focal
ments thereof with reference to the accompanying drawings, 15 spot dimension is characterized by the value wherein:
FIG. 1 is a schematic diagram of apparatus for carrying ((lamdayD)*F,
out a method of creating an image inside a transparent where ... is the radiation wavelength of the laser
material, using a laser beam, according to the invention; 2Q used;
FIG. 2 is a schematic diagram of sharp focusing of a beam F is the focal length of the focusing lens,
of the pulsed laser for realization of the method proposed in The intensity of the laser radiation at a focal spot 9 is
the present invention; and found from the formula
FIG. 3 is a schematic diagram of reproduction of a copy
of an image stored in a computer memory performed by a 25
laser beam inside a specimen of a transparent material. where P is the power of laser radiation,
S is the effective area of the focal spot.
DESCRIPTION OF THE PREFERRED It results ftom this formula faat me intensity of laser
EMBODIMENTS radiation is proportional to the following expression
To provide a better understanding of the essence of the 30 ,. .,«^^ .
* . e , . (P/(lamda)squared)*(D/F)squared.
proposed method it is expedient first to consider a schematic
diagram of the apparatus for carrying out said method as When calculating the value of the radiation intensity at the
shown in FIG. 1. focus of a multimode laser the above expression is to be
The device comprises a solid-state pulsed laser 1 fixed in divided by squared ratio between the beam divergence of the a stationary position; a variable focal length defocusing 35 laser used and diffraction-limited divergence thereof. Corndivergent lens 2 fixed stationary on the axis of the laser beam pensation of focusing loss by increasing the radiation power 3; a focusing lens 4 located on the axis of the laser beam 3 will result in an undesired increase in the part played by wherein lens 4 can be moved controllably along said axis self-focusing. Increase in the second factor in the above with the aid of actuator 5; a specimen 6 of a transparent expression is restricted by aberration of the focusing lens 4. material arranged across the path of the focused laser beam 40 The parenthesized relation D/F defines the focusing 3, the specimen 6 being capable of moving in a plane sharpness, whence it ensues that the maximum laser radiaorthogonal to the laser beam 3, with the aid of a drive 7. tion intensity in the focus point for a given radiation power
The drive 7 may be in fact a plotter of the heretofore- is attainable at a sharpest aberration-free focusing of a
known construction. single-mode laser beam.
. *o- -j J * <_ i A. c *u 45 The shorter the focal length F of the defocusing divergent
A computer 8 is provided to control the operation of the , „ , it , &. , ,. J> *
1 „„*,,„tTM. c „„a ^„-„= 1 w^i;TMi„TM-„„ lens 2, the sharper the focusing of the laser radiation and the
pulsed laser 1, actuator 5 and drive 7 for displacing the . ,TM . . .. ^ .. .
% , . , . , T ..... ..u higher its intensity. Thus, a desired intensity of laser-induced
focusing lens 4 and the specimen 6. In addition, the com- , , , , ,
o <_ 1 *u t 111 A f ■ A- <- breakdown at the focus point is attainable with lower power puter 8 controls the focal length of the defocusmg divergent ^ ^ 1 f . , . , . . ., t r, 1 i„ consumption, thereby making it possible to create a laserlens 2 which is similar to the commonly known photo- , , , . , . „ ,.
,. , ... . f , , .u 50 produced destruction area having smaller linear dimensions.
graphic camera lenses with a variable focal length. r _ . , ,. ^ '5 ^ . , ., „
3. , , , , . ,, r Consequently, by adjusting the focal length of the lens 2
It is a TEMro laser that proves to be most suitable for the and hence ^ lasef ... powgr Qne can control ±e gize
purpose. Qj ^ destruction area in the specimen 6 made of a transSelection of such a laser is due to the greatest brightness parent material, which allows reproducing a half-tone picof radiation emitted by said laser at a given power. 55 turei
Use of a laser featuring a lower brightness-to-power ratio In principal, the proposed technology of creating a threeleads to an undesirable effect of self-focusing. It has been dimensional or two-dimensional image in a light-transparent found that exceeding the self-focusing threshold by laser material can be applied under manual control of the laser 1 radiation power results in laser beam self-trapping into a by changing the laser beam focusing sharpness and the number of strings. To avoid this disadvantage one must 60 radiation power thereof before each shot. However, the provide that laser radiation power be lower than self- image creation process will in such case be of low producfocusing threshold. tivity. To accelerate the process a computer monitoring of
Nevertheless, in order to initiate breakdown at the focal system operation is used, which can be illustrated by a
point it is necessary to exceed the threshold breakdown detailed description of the schematic diagram presented in
intensity at a given point. It is the laser type selected herein 65 FIG. 3.
that features the maximum intensity-to-radiation power ratio An image 10 of the object to be reproduced is written into
at the focal point at a given focusing geometry. the memory of computer 8 as a number of sections made by
