Coherent light generators – Particular beam control device – Producing plural wavelength output
Reexamination Certificate
2000-07-31
2003-11-04
Ip, Paul (Department: 2828)
Coherent light generators
Particular beam control device
Producing plural wavelength output
C355S067000
Reexamination Certificate
active
06643300
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
The present application is based on Patent Application No. 11-220970 filed in Japan, the content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a laser irradiation optical system, and specifically relates to a laser irradiation optical system which divides a laser beam, shapes each laser beam after division, and emits each laser beam after shaping.
2. Description of the Prior Art
A characteristic of a laser beam is the ability to increase intensity and reduce the beam width, for diversified fine processing of an object surface. In recent years, increased processing efficiency has been achieved by performing the same process at a plurality of parts by dividing a laser beam emitted from a laser light source into a plurality of laser beams, and irradiating an object with the laser beams after division of the laser beam.
It is necessary to equalize the intensity of the laser beams after division because the different parts of the object cannot be processed equally due to differences in intensity between the emitted laser beams. The intensity distribution of each laser beam must be set in accordance with shape of the object being processed because the object is processed in a shape corresponding to the intensity distribution of the laser beam. For example, when forming a hole having a square cross section and a fixed depth in an object, the contour of the cross section perpendicular to the optical path must be rectangular, and the laser beam must have a uniform intensity distribution within this cross section.
Accordingly, the laser irradiation optical system used for such purpose not only simply divides the laser beam emitted from the light source, but also must equalize the intensity of all laser beams after division to attain a desired intensity distribution of each laser beam in a cross section parallel to the optical path and in a cross section perpendicular to the optical path. In general, the intensity distribution in a cross section perpendicular to the optical path of the laser beam emitted from a light source is a Gaussian type distribution, and is not suitable to be used directly in most cases. For this reason, the intensity distribution of the laser beam is converted, i.e., shaped, by the laser irradiation optical system.
The construction of a conventional laser irradiation optical system is briefly shown in FIG.
15
. This laser irradiation optical system
7
divides a laser beam L
1
emitted from a laser light source
71
into four laser beams L
2
, and equalizes the intensity distribution of each laser beam L
2
in a cross section perpendicular to the optical path. Three half-mirrors
73
are provided to divide the laser beam L
1
, and the transmittance and reflectivity rate of the three half-mirrors
73
are set so as to equalize the intensity of the laser beams L
2
after division.
The laser means L
2
after division are directed to a light shield
77
provided with openings
77
a
having identical size and shape and disposed at equal distances via the total reflecting mirror
74
. The light shield
77
transmits only the center part of the laser beam L
2
having a Gaussian distribution so as to render a uniform intensity distribution in a cross section perpendicular to the optical path, and regulates the shape of the contour of this cross section via the shape of the opening
77
a.
A beam expander
72
for broadening the beam width of the laser beam L
1
is arranged on the optical path from the light source
71
to the half-mirror
73
, and a lens
75
for converging the laser beam L
2
on the light shield
77
is arranged on the optical path of each divided laser beam L
2
. The four lenses
75
have identical performance, and the distance from each lens
75
to the light shield
77
is equal. A reducing optical system
78
is provided on the optical path of the laser beam L
2
transmitted through the opening
77
a
, and each laser beam L
2
is condensed in beam width and mutual spacing via the reducing optical system
78
and irradiates the irradiation object surface S.
In laser irradiation device
7
, the divided laser beams L
2
are shaped by the opening
77
a
of the light shield
77
, the lens
75
, and the reducing optical system
78
. The main element among the aforesaid elements fulfilling this function is the opening
77
a
which regulates the intensity distribution in a direction perpendicular to the optical path. The condition of the shaping of the divided laser beam L
2
by the opening
77
a
of the light shield
77
is shown schematically in FIG.
16
.
In this laser irradiation device, the division of the laser beam emitted from the light source occurs in several stages. For this reason, the overall structure is enlarged, there are many optical elements, and the relative positions of the elements cannot be easily set. This problem becomes pronounced as more laser beams are produced after division.
The divided laser beams have a Gaussian type distribution similar to the laser beam before division, and the range in which the intensities are near fixed is narrow. Accordingly, the majority of the laser beam is eliminated in shaping, such that there is poor usage efficiency of the laser beam from the light source. In the example of
FIG. 16
, only one half of the laser emitted from the light source is used.
Laser beam division also can be accomplished by a diffraction element; when such an element is used, the beam can be divided once, and the overall structure can be expected to be made more compact. However, there is no example of use of a diffraction element for division in laser irradiation optical systems which shape the beam after dividing the beam. This is because the laser beams are overlap directly after division, and the shaping of each laser beam is difficult in this state, the direction of travel of each laser beam differs after division, and setting the conditions for managing the direction of travel and the conditions for shaping are difficult.
SUMMARY OF THE INVENTION
An object of the present invention is to improve a compact laser irradiation optical system for dividing and shaping a laser beam into a plurality of laser beams and emitting the laser beams after shaping.
A particular object of the present invention is to provide a laser irradiation optical system which has little loss of the laser when shaping.
These objects are attained by a laser irradiation optical system having the following construction.
A laser irradiation optical system comprising a dividing means for dividing a first entering laser beam once, and producing a plurality of second laser beams having beam widths equal to the beam which of the first laser beam and advancing in mutually different directions; a condensing means for condensing each second laser beam to mutually advance in near the same direction; and a shaping means for converting the intensity distribution of a cross section perpendicular to the optical path of each second laser beam in the optical paths of the mutually separated second laser beams.
The division means divides the entering first laser beam into a plurality of second laser beams, but since this division occurs only once, the overall construction of the laser irradiation optical system is compact. The division means may divide the first laser beams in only one direction, or may divide the first laser beam in two directions. All the second laser beams obtained by division have approximately equal beam widths. Since it is also possible for the division means to approximately equalize the intensities of all the second laser beams, all the second laser beams can be rendered equivalent excluding the different directions of travel.
The second laser beams are set to advance in approximately the same direction via the condensing means. Accordingly, the second laser beams can irradiate the irradiation object from identical directions. Moreover, the condensing means produces a condensed beam of each second laser beam, such that
Ip Paul
Nguyen Phillip
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