Coherent light generators – Particular pumping means – Pumping with optical or radiant energy
Reexamination Certificate
2002-01-24
2004-11-02
Wong, Don (Department: 2828)
Coherent light generators
Particular pumping means
Pumping with optical or radiant energy
C372S069000, C356S337000, C356S340000
Reexamination Certificate
active
06813303
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a laser oscillator using a semiconductor laser, and a light scattering type particle detector for detecting particles contained in sample fluid using the laser oscillator.
2. Description of the Prior Art
In a conventional light scattering type particle detector as shown in
FIG. 22
, a laser oscillator comprises a laser medium
200
and a reflecting mirror
201
, and a flow path
202
defined by fluid to be detected is provided between the laser medium
200
and the reflecting mirror
201
. Pumping laser light Le emitted from a semiconductor laser
203
is condensed with a condenser lens
204
to irradiate upon the laser medium
200
, and thereby the laser medium
200
is pumped. A particle detecting region
205
is a region where laser light La resonating between the laser medium
200
and the reflecting mirror
201
intersects the flow path
202
. Scattered light Ls being a scattered portion of the resonating laser light La in the particle detecting region
205
is received at a light receiving portion
206
. Particles contained in sample fluid are detected by electrical signals generated based on the intensity of the scattered light Ls which is received.
Further, in the prior art as disclosed in Japanese Patent Publication No. 6-58318, an antireflection coating through which the pumping wavelength of the semiconductor laser
203
(the pumping wavelength of the laser medium
200
) can penetrate and a high reflection coating having a characteristic of reflecting the oscillating wavelength of the laser medium
200
are applied onto the surface of the laser medium
200
opposite to the condenser lens
204
.
The conventional light scattering type particle detector as shown in
FIG. 22
has a drawback that the pumping laser light Le is incident on the semiconductor laser
203
as feedback light even with the antireflection coating through which the pumping wavelength of the semiconductor laser
203
can penetrate. Another drawback exists wherein the laser light La resonating between the laser medium
200
and the reflecting mirror
201
penetrates through the laser medium
200
so as to be incident on the semiconductor laser
203
as feedback light even with the high reflection coating having a characteristic of reflecting the oscillating wavelength of the laser medium
200
. Such feedback light causes fluctuation to the intensity of the pumping laser light Le emitted from a semiconductor laser
203
and the resonating laser light La and such fluctuation deteriorates the signal
oise ratio. It is acknowledged that when laser light emitted from the semiconductor laser is later incident on the semiconductor laser again because of reflection or the like, such feedback light causes fluctuation noise.
In another conventional light scattering type particle detector as shown in
FIG. 23
, a laser oscillator comprises a laser medium
215
and a reflecting mirror
216
, and a flow path
217
defined by fluid to be detected is provided between the laser medium
215
and the reflecting mirror
216
. Pumping laser light Le emitted from a semiconductor laser
218
is condensed with a condenser lens
219
to irradiate upon the laser medium
215
, and thereby the laser medium
215
is pumped. A particle detecting region
220
is a region where laser light La resonating between the laser medium
215
and the reflecting mirror
216
intersects the flow path
217
. A scattered portion of the resonating laser light La in the particle detecting region
220
is received at a light receiving portion (not shown in the drawing). Particles contained in the sample fluid are detected by electrical signals generated based on the intensity of the scattered light which is received.
A case is comprised of a hollow first setting block
222
and a hollow second setting block
223
. The laser medium
215
is fixed to the second setting block
223
and the second setting block
223
is fixed to the first setting block
222
. A light receiving case (not shown in the drawing) for housing the light receiving portion is fixed to the side surface of the first setting block
222
.
If there is no error in the fixation of the laser medium
215
to the second setting block
223
or the like, laser light La irradiated from the laser medium
215
goes in the perpendicular direction with respect to the end surface (irradiation surface) of the laser medium
215
and in the direction corresponding to the core axis of the first setting block
222
.
However, in fact, error arises in the fixation of the laser medium
215
to the second setting block
223
, and resultantly the laser light La is not oriented to travel in the direction corresponding to the core axis of the first setting block
222
. In this case, it is necessary to adjust the setting angle of the reflecting mirror
216
with respect to the first setting block
222
so that the laser light La reflected by the reflecting mirror
216
can reflect accurately to the laser medium
215
.
Further, even if the setting angle of the reflecting mirror
216
is adjusted to be the most preferable angle to make the laser light La reflected by the reflecting mirror
216
reflect accurately to the laser medium
215
, the irradiating direction of the oscillated laser light La does not coincide with the core axis of the first setting block
222
. Therefore, it may be necessary to shift the flow path
217
which is positioned on the assumption that the irradiating direction of the oscillated laser light La coincides with the core axis of the first setting block
222
. The shift of the flow path
217
changes the position of the particle detecting region
220
. Depending on this, it is necessary to adjust the setting position of the light receiving case for housing the light receiving portion with respect to the first setting block
222
.
Accordingly, the conventional light scattering type particle detector exhibits drawbacks including that complicated adjustment is required for the position adjustment of the flow path
217
and the setting adjustment of the light receiving case with respect to the first setting block
222
, and that a lot of work is also required for the assembly of the whole apparatus, including tasks such as setting the angle adjustment of the reflecting mirror
216
in the case where there is error in the fixation.
Further, as other light scattering type particle detectors, two types as disclosed in Japanese Patent Publication No. 6-58318 are known. One type uses a He—Ne gas laser as a laser medium and the other uses a solid-state laser as a laser medium.
In either type, a flow path
232
defined by sample fluid flowing from an inlet
230
to an outlet
231
is provided within a laser resonator as shown in
FIG. 24. A
particle detecting region
233
is a region where laser light La having a circular transverse mode pattern intersects the flow path
232
.
Recently, there is a tendency that electronic devices of high precision are manufactured in clean surroundings such as a clean room. The number of particles suspending within a clean room is controlled so as to ensure the cleanness of the clean room. It is required that a large volume of sample air is taken into a particle detector for controlling the number of particles in the clean room.
Therefore, it is necessary to increase the cross section of a flow path for flowing a large volume of sample air through the flow path within a predetermined period of time. Also, it is necessary to increase the cross section of laser light in accordance with the cross section of the flow path and thereby define a larger particle detecting region for detecting all particles within sample air passing the flow path.
However, if the cross section of laser light is increased in the conventional light scattering type particle detector, the following problems are caused:
(1) In a light scattering type particle detector using He—Ne gas laser as a laser medium, a He—Ne laser medium is comprised of a capillary glass tube having a circular cross section
Matsuda Tomonobu
Minakami Takashi
Nakajima Tsutomu
Sasaki Kenji
Al-Nazer Leith A
Blackman William D.
Carrier Joseph P.
Carrier Blackman & Associates P.C.
Rion Co. Ltd.
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