Coherent light generators – Particular resonant cavity – Specified cavity component
Reexamination Certificate
2002-02-07
2004-08-31
Vu, David (Department: 2828)
Coherent light generators
Particular resonant cavity
Specified cavity component
C372S100000, C372S101000, C372S103000, C372S108000
Reexamination Certificate
active
06785319
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a narrow band ultraviolet laser device.
BACKGROUND ART
In an ultraviolet laser device, an art of band-narrowing, which narrows a spectral bandwidth of laser light and stabilize its center wavelength by mounting a wavelength selection element in a resonator, is conventionally known (Refer to, for example, Japanese Patent Laid-open No. 10-313143).
Hereinafter, the prior art will be explained with an excimer laser device as an example.
FIG. 7
is an explanatory block diagram of a narrow band excimer laser device
1
according to the prior art. In
FIG. 7
, the excimer laser device
1
includes a laser chamber
2
with a laser gas being sealed therein, and a band-narrowing unit
10
for narrowing a bandwidth of laser light
11
oscillated from this laser chamber
2
. The laser light
11
oscillated by electric discharge inside the laser chamber
2
is incident on the band-narrowing unit
10
provided outside and behind the laser chamber
2
.
The laser light
11
incident on the band-narrowing unit
10
is expanded by prisms
32
and
32
, and is incident on a grating
33
. Only the laser light
11
with a predetermined wavelength is returned in the same direction as the incident light by the grating
33
, then it is incident on the laser chamber
2
again and is emitted from a front mirror
8
. Subsequently, it is incident on a processing machine
15
to be a light source for performing precision machining inside it.
In this situation, part of the laser light
11
sometimes hits on end portions of the prisms
32
and the grating
33
inside the band-narrowing unit
10
. When such reflected light the bandwidth of which is not narrowed (this is called undesired laser light
11
A) returns to the laser chamber
2
, optical quality of the laser light
11
such as a center wavelength, spectral bandwidth, and the like is degraded. Further, as a result that the laser light
11
is incident on an optical component from the surfaces other than a predetermined incident surface, heat sometimes generates and thereby the optical component is deformed. Furthermore, when the laser light
11
is incident on the grating
33
at the angles other than a predetermined incident angle, wavelength selection by the grating
33
is not favorably performed, and thereby the optical quality of the laser light
11
is degraded.
In order to avoid the above, a first light shielding element
37
A for removing the undesired laser light
11
A is provided at a position where the laser light
11
is incident on the band-narrowing unit
10
, and a second light shielding element
37
B is provided inside the band-narrowing unit
10
. Further, a third light shielding element
37
C is provided inside the front mirror
8
to shape a beam form of the laser light
11
into a predetermined form suitable for processing.
FIG. 8
shows the forms of the light shielding elements
37
A to
37
C. In
FIG. 8
, the light shielding elements
37
A to
37
C have light shielding sections
49
A to
49
C in a plate form for removing the undesired laser light
11
A, and light transmitting sections
47
A to
47
C constituted by rectangular openings for transmitting the laser light
11
, respectively. When the laser light
11
is radiated to the light shielding elements
37
A to
37
C, the undesired laser light
11
A hit on the light shielding sections
49
A to
49
C is irregularly reflected, then deviated from an optical path, and is absorbed in a cover or the like not shown for covering the excimer laser device
1
. The residual laser light
11
passes through the light transmitting sections
47
A to
47
C, and is shaped into a rectangular beam form.
However, the above-described prior art has the disadvantages as described below.
Specifically, according to the prior art, there is no description regarding the material of the light shielding elements
37
A to
37
C, and metal is generally used. When the laser light
11
is radiated to the light shielding elements
37
A to
37
C, part of it is absorbed in the light shielding sections
49
A to
49
C, and the light shielding sections
49
A to
49
C are beginning to have heat. In this situation, gases, such as, for example, air and an inert gas exist inside the light transmitting sections
47
A to
47
C. Accordingly, temperature gradient occurs to the gases as a result of heat generation from inner edges
50
A to
50
C of the light shielding sections
49
A to
49
C. Specifically, the temperature of the gases near the inner edges
50
A to SOC of the light transmitting sections
47
A to
47
C rises to be high, but the temperature of the gases near a center does not rise so much.
As a result, indexes of refraction of the light transmitting sections
47
A to
47
C become nonuniform, and the gases act as if they were lenses, whereby a wavefront of the laser light
11
passing through the light transmitting sections
47
A to
47
C is distorted. Thus, there arises the disadvantage that the beam form of the laser light
11
emitted from the excimer laser device
1
is distorted or the spectral bandwidth is increased, thereby degrading the quality of the laser light
11
, and processing is not favorably performed.
Further, temperature gradient hardly exists at the time of the start of the laser oscillation, but as the laser light is oscillated for a long period of time, the temperature gradient occurs to balance, and therefore the indexes of refraction of the light transmitting sections
47
A to
47
C at the time of the start of the oscillation changes after a lapse of long period of time. Thus, even if the incident angle of the laser light
11
onto the grating
33
is adjusted so that the optical quality becomes favorable at the time of start of oscillation, the wavefront is distorted with a lapse of time, and the optical quality is degraded. Further, there exists the disadvantage that the beam form and the beam center position are varied to give an adverse effect on processing.
DISCLOSURE OF THE INVENTION
The present invention is made in view of the above-described disadvantages, and its object is to provide a narrow band ultraviolet laser device which can restrict a change in temperature gradient at light transmitting sections and maintain laser light at a high grade.
In order to attain the above-described object, a first aspect of an ultraviolet laser device according to the present invention is a narrow band ultraviolet laser device comprising light shielding elements having
light transmitting sections each constituted by an opening for transmitting laser light, and
light shielding sections that surround the light transmitting sections, remove undesired laser light from an optical path and shape the laser light into a predetermined form, and
includes the constitution in which healing means for heating the light transmitting sections are included in the vicinity of the light shielding elements.
According to the above constitution, the heating means for heating the light transmitting sections are included in the vicinity of the light shielding elements. Consequently, gases inside the light transmitting sections are entirely heated and become substantially uniform in temperature, thus making it possible to reduce temperature gradient of the gases inside the light transmitting sections, which occurs when the laser light is radiated to the light shielding plate. Accordingly, ununiformity in the indexes of refraction of the light transmitting sections is reduced, and therefore a wavefront is not distorted when the laser light passes through the light transmitting sections, thus making it possible to obtain the laser light at a high grade. Further, by heating the entire heat shielding elements in advance, a change in the indexes of refraction of the light transmitting sections between the time of starting laser light oscillation and the time after a lapse of time can be reduced. Accordingly, if the positions and the angles of the optical components in the band narrowing unit at the time of start of oscillation are adjusted, a change in the wavefront with a
Akita Jun
Ariga Tatsuya
Itoh Noritoshi
Kumazaki Takahito
Armstrong, Kratz, Quintos Hanson & Brooks, LLP.
Komatsu Ltd.
Rodriguez Armando
Vu David
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