Laser surface treatment method and apparatus for practicing same

DETAILED DESCRIPTION An object of the present invention is to provide a surface treatment method capable of treating an object surface so that the surface is provided with high anisotropy, without applying the light to the same surface, or with the intensity of the incident light limited to a level at which the damage to the surface does not occur.
This object can be achieved by exciting or decomposing only such gas particles that have speeds within a predetermined range with the light of a narrow line width to thereby treat the surface of a substrate.
The gas particles move at various speeds, and the wavelengths of the light absorbed by the respective gas particles vary depending upon the speeds thereof.
The speed referred to above is a vector having a direction.
Let C equal the speed of the light, and .
lambda.
.
sub.
O the wavelength of the light which is absorbed by the stationary gas particles.
The wavelength of the light absorbed by a gas particle having a speed V in the direction of light propagation becomes as follows due to the Doppler effect.
##EQU1## If the light of a specific wavelength .
lambda.
is applied to a substrate, only the gas particles that have the speed V in the direction of light propagation can be excited.
(The gas particles having a speed in the direction of the light propagation of zero can be excited selectively, especially, with the light of a specific wavelength .
lambda.
=.
lambda.
.
sub.
O.
) Since it is difficult from a practical standpoint to obtain the light of a specific wavelength, the light of a narrow line width .
DELTA.
.
lambda.
is used.
For example, if the light of a line width of FWHM (full width at half maximum) of 2.
times.
10.
sup.
-6 .
lambda.
.
sub.
O is used, the following equation can be established for defining a narrow line width light as that term is used herein.
##EQU2## In accordance with the equation (1), .
DELTA.
V=2.
times.
10.
sup.
-6 .
times.
C=600 m.
s.
Namely, the velocity distribution in the direction of light propagation of the gas particles to be excited can be set to both -300 m/s