JP2002141587A - Laser oscillator and light scattering particle detector comprising it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light scattering particle detector in which a particle having a relatively small size can be detected accurately by suppressing fluctuation in the intensity of laser light cased by a pumping laser light impinging on a semiconductor laser as a returning light, thereby ensuring a sufficiently high signal/noise ratio in particle detection. SOLUTION: A laser oscillator 1 is provided with a specified angle θ between the optical axis 11a of a semiconductor laser 11 radiating a pumping laser light Le and the optical axis 13a of a laser medium 13 being pumped by the pumping laser light Le to radiate a laser light La. A laser beam La emitted from the laser oscillator 1 is focused at a channel 2 formed by a sample fluid to form a particle detecting region 8, and particles contained in that region 8 are detected by receiving a scattering light Ls generated by the laser beam La at a light receiving section 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a laser oscillator using a semiconductor laser and a light scattering type particle detector for detecting particles contained in a sample fluid using the same.

[0002]

2. Description of the Related Art As a conventional light scattering type particle detector, as shown in FIG. 3, a laser medium 1 constituting a laser oscillator is used.
A flow path 102 is formed by a fluid to be subjected to particle detection between the laser medium 00 and the reflecting mirror 101, and the laser light Le for excitation of the semiconductor laser 103 is condensed on the laser medium 100 by the condenser lens 104 to excite the laser medium 100. And the laser medium 10
0 and the laser beam La resonating between the reflecting mirror 101 and the flow path 1
A portion where 02 intersects is a particle detection region 105, and the scattered light Ls generated in the particle detection region 105 by the resonating laser light La is received by the light receiving unit 106, and an electric signal corresponding to the intensity of the scattered light Ls is used in the sample fluid. A device that detects particles contained in a gas is known.

Further, as described in Japanese Patent Publication No. 6-58318, the condenser lens 10 of the laser medium 100 is
4 is coated with an antireflection film that allows the excitation wavelength of the semiconductor laser 103 (the pumping wavelength of the laser medium 100) to pass therethrough and a high reflection film that has the property of reflecting the oscillation wavelength of the laser medium 100.

[0004]

However, in the light scattering type particle detector shown in FIG. 3, an antireflection film for passing the excitation wavelength of the semiconductor laser 103 is provided on the surface of the laser medium 100 facing the condenser lens 104. Even if the laser medium 100 is coated, the excitation laser light Le is incident on the semiconductor laser 103 as return light, or if the laser medium 100 is coated with a high-reflection film having a characteristic of reflecting the oscillation wavelength of the laser medium 100, The laser light La that resonates with the semiconductor laser 103 passes through the laser medium 100 and again emits the semiconductor laser 103.
In this case, the intensity of the laser light La resonating due to the return light fluctuates, and this fluctuation causes a reduction in the signal-to-noise ratio in particle detection.

The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to cause an excitation laser beam to enter a semiconductor laser as return light. A laser oscillator that reduces fluctuations in the intensity of laser light, and a light-scattering particle detector that uses this laser oscillator to sufficiently increase the signal-to-noise ratio in particle detection and accurately detect particles with a relatively small particle size It is intended to provide.

[0006]

According to a first aspect of the present invention, a laser beam for excitation emitted by a semiconductor laser is condensed on a laser medium by a condenser lens, and the laser medium is excited. A laser oscillator that emits laser light at a predetermined angle between the optical axis of the semiconductor laser and the optical axis of the laser medium.

According to a second aspect of the present invention, a laser beam emitted by the laser oscillator according to the first aspect is converged on a flow path formed by a sample fluid to form a particle detection region, and the particle detection region is included in the particle detection region. The particles are detected by receiving the scattered light generated by the laser light.

[0008]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Here, FIG. 1 is a schematic configuration diagram of a light scattering type particle detector according to the present invention, and FIG. 2 is a schematic configuration diagram of a light scattering type particle detector according to another embodiment of the present invention.

The light scattering type particle detector according to the present invention is shown in FIG.
As shown in FIG. 1, a laser oscillator 1 as a light source, a flow path 2 formed by a fluid to be detected, and a light receiving unit 3 for receiving scattered light Ls are provided.

The laser oscillator 1 includes a semiconductor laser 11 for emitting an excitation laser beam Le, a condenser lens 12 for condensing the excitation laser beam Le, and an excitation laser beam Le collected by the condenser lens 12. The laser medium 13 includes a laser medium 13 that receives and excites the laser light and emits the laser light La, and a reflecting mirror 14 that is installed to face the laser medium 13 with the flow path 2 interposed therebetween and reflects the laser light La emitted by the laser medium 13.

As the laser medium 13, for example, Nd: Y
VO ₄ , Nd: YAG or the like is used. Laser medium 1
An anti-reflection film that passes the excitation wavelength of the semiconductor laser 11 (the pumping wavelength of the laser medium 13) and a reflection film that reflects the oscillation wavelength of the laser medium 13 are formed on the end surface 13a of the third condensing lens 12 side. An antireflection film for the oscillation wavelength of the laser medium 13 is formed on the end face 13 b of the laser medium 13 on the side of the reflecting mirror 14.

Further, a predetermined angle θ is provided between the optical axis 11a of the semiconductor laser 11 and the optical axis 13c of the laser medium 13. The angle θ is the excitation laser light Le reflected by the end face 13 a of the laser medium 13 or the laser light La transmitted by the end face 13 a of the laser medium 13 after being reflected by the reflecting mirror 14.
However, the angle is set such that the light does not enter the light emitting portion of the semiconductor laser 11 as the return light, or the angle at which the amount of light is reduced even if it enters.

When an anti-reflection film is formed on the end face 13a of the laser medium 13 after the angle θ is set, the anti-reflection film depends on the incident angle of the excitation laser beam Le incident on the end face 13a. Is desirably coated in accordance with the range of the incident angle of the excitation laser beam Le so that is hardly changed.

If the end face 13a of the laser medium 13 is already provided with an anti-reflection film, the amount of transmission of the excitation laser beam Le to the laser medium 13 does not decrease according to the characteristics of the anti-reflection film. As described above, considering the range of the incident angle of the excitation laser light Le incident on the end face 13a,
It is desirable to set the angle θ.

Furthermore, it is necessary to change the setting of the angle θ depending on the size of the half angle of the condensing lens 12. As a characteristic of the semiconductor laser 11, the divergence angle of the beam is large (for example, about 30 °). Therefore, in order to prevent the transmission light amount of the excitation laser light Le from the laser medium 13 from decreasing, the collection lens 12 This is because it is necessary to set the angle θ in consideration of the half-angle of light.

For example, a condensing lens 1 having a converging half angle of 40 °
When 2 is used, the angle θ is desirably set to about 30 °. This makes it possible to reduce return light from the end surface 13a of the laser medium 13 while maintaining the transmission light amount of the excitation laser light Le to the laser medium 13 at a desired level.

Therefore, the predetermined angle θ provided between the optical axis 11a of the semiconductor laser 11 and the optical axis 13c of the laser medium 13 depends on the characteristics of the antireflection film formed on the end face 13a of the laser medium 13, Are set in consideration of the range of the incident angle of the excitation laser beam Le incident on the end face 13a of the light-receiving surface 13a, the half-angle of the light condensing lens 12, and the like.

The flow path 2 is formed by suctioning a fluid to be detected by a suction pump (not shown) connected downstream of the outlet 6 and flowing the fluid from the inlet 7 to the outlet 6. Then, a portion where the laser beam La and the flow path 2 intersect becomes the particle detection region 8.

The light receiving section 3 includes a condenser lens 9 for condensing scattered light Ls generated in the particle detection area 8 and a condensed scattered light Ls
A photodiode 10 for photoelectrically converting the light, receives scattered light Ls by the laser light La applied to the particles in the particle detection region 8 when the fluid contains particles, and responds to the intensity of the scattered light Ls. Outputs electrical signals.

The operation of the light scattering type particle detector according to the present invention configured as described above will be described. Semiconductor laser 1
When the laser beam 1 emits the excitation laser beam Le, the excitation laser beam Le is condensed by the condenser lens 12 to the end face 1 of the laser medium 13.
Focus on 3a. At this time, even if the excitation laser light Le is reflected by the end face 13a of the laser medium 13, the semiconductor laser 11
Since the predetermined angle θ is provided between the optical axis 11a of the laser medium 13 and the optical axis 13c of the laser medium 13, the excitation laser light Le does not return to the light emitting portion of the semiconductor laser 11.

After the laser light La emitted from the laser medium 13 excited by the excitation laser light Le is reflected by the reflecting mirror 14, a part of the laser light La passes through the laser medium 13 and is emitted to the condenser lens 12 side. However, since the predetermined angle θ is provided between the optical axis 11a of the semiconductor laser 11 and the optical axis 13c of the laser medium 13, a part of the laser light La does not return to the light emitting portion of the semiconductor laser 11. Absent.

Therefore, in addition to providing an antireflection film for passing the excitation wavelength of the semiconductor laser 11 and a reflection film for reflecting the oscillation wavelength of the laser medium 13 on the end face 13a of the laser medium 13, the optical axis 11a of the semiconductor laser 11 By providing a predetermined angle θ with the optical axis 13c of the medium 13,
The excitation laser light Le emitted by the semiconductor laser 11 can be further reduced from returning to the light-emitting portion of the semiconductor laser 11 or a part of the laser light La returning to the light-emitting portion of the semiconductor laser 11. Since the intensity of the light Le does not fluctuate, the laser light L emitted from the laser medium 13
The degree of fluctuation of the intensity a can be reduced.

Then, the light receiving section 3 receives the scattered light Ls by the laser light La applied to the particles in the particle detection area 8, and outputs an electric signal corresponding to the intensity of the scattered light Ls.
The presence of particles, the size of the particle size, and the like can be recognized based on the level of the electric signal output from the light receiving unit 3. Here, the laser light L
Since the signal-to-noise ratio in particle detection is not reduced by reducing the fluctuation of the intensity of a, particles having a relatively small particle size can be detected accurately.

Next, as a light scattering type particle detector according to another embodiment of the present invention, as shown in FIG. 2, a flow path 2 formed by a fluid to be detected is connected to a resonance region of a laser beam La. Instead of being provided inside the laser oscillator 21, it may be provided outside the laser oscillator 21, and a portion where the laser beam La emitted outside the laser oscillator 21 intersects the flow path 2 may be used as the particle detection region 8.
However, in this case, it is necessary to use a semi-transparent mirror 24 instead of the reflecting mirror 14 shown in FIG.

Accordingly, the laser oscillator 21 is composed of the semiconductor laser 11 for emitting the excitation laser light Le, the condenser lens 12 for condensing the excitation laser light Le, and the excitation laser light collected by the condenser lens 12. A laser medium 13 that receives and excites Le and emits a laser beam La, and a laser beam L that is installed facing the laser medium 13 and emitted by the laser medium 13
It consists of a semi-transparent mirror 24 reflecting a.

A laser beam La resonating between the laser medium 13 and the semi-transparent mirror 24 is generated, and a part of the laser beam La passes through the semi-transparent mirror 24 and irradiates the particle detection region 8. The description of the same components as those shown in FIG. 1 will be omitted.

The operation of the light scattering type particle detector according to another embodiment of the present invention configured as described above will be described with reference to FIG.
Since the operation is the same as that of the light scattering type particle detector shown in FIG.

In the case of the light scattering type particle detector shown in FIG. 2, a flow cell made of a transparent material is provided between the inlet 7 and the outlet 6 of the flow channel 2 so that the liquid flows into the flow channel 2. Since the liquid can flow, particles in the liquid can be detected.

[0029]

As described above, according to the first aspect of the present invention, since the predetermined angle is provided between the optical axis of the semiconductor laser and the optical axis of the laser medium, the excitation laser light returns As a result, the intensity of the excitation laser light does not fluctuate, so that the fluctuation of the intensity of the laser light emitted from the laser medium can be reduced.

According to the second aspect of the present invention, since a predetermined angle is provided between the optical axis of the semiconductor laser and the optical axis of the laser medium, the laser beam for excitation enters the semiconductor laser as return light. Can be prevented, and the intensity of the excitation laser light does not fluctuate, so that the fluctuation of the intensity of the laser light emitted from the laser medium can be reduced. Therefore, particles having a relatively small particle size can be accurately detected.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a light scattering type particle detector according to the present invention.

FIG. 2 is a schematic configuration diagram of a light scattering type particle detector according to another embodiment of the present invention.

FIG. 3 is a schematic configuration diagram of a conventional light scattering type particle detector.

[Explanation of symbols]

1, 21 ... laser oscillator, 2 ... flow path, 3 ... light receiving section, 6 ...
Outlet, 7 ... Inlet, 8 ... Particle detection area, 1
1 ... Semiconductor laser, 11a ... Optical axis of semiconductor laser, 12
... Condenser lens, 13 ... Laser medium, 13c ... Optical axis of laser medium, 14 ... Reflection mirror, 24 ... Semi-transmissive mirror, La ... Laser light, Le ... Excitation laser light, Ls ... Scattered light, θ ... Predetermined angle .

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kenji Sasaki 3-20-41 Higashimoto-cho, Kokubunji-shi, Tokyo Rion Co., Ltd. (72) Inventor Tsutomu 20-41 Higashimoto-cho, Kokubunji-shi, Tokyo Rion F term in reference (reference) 5F072 AB20 JJ05 KK06 PP07 YY20

Claims (2)

[Claims] 1. A laser oscillator, wherein a laser beam for excitation emitted by a semiconductor laser is focused on a laser medium by a focusing lens, and the laser medium is excited to emit laser light. A laser oscillator, wherein a predetermined angle is provided between the optical axis of a laser medium and an optical axis of the laser medium. 2. A laser beam emitted by the laser oscillator according to claim 1 is condensed on a flow path formed by a sample fluid to form a particle detection region, and particles contained in the particle detection region are irradiated with the laser light. A light scattering type particle detector, which receives and detects scattered light generated by the light scattering type particle detector.