LASER GAS ANALYSIS DEVICE

Abstract

This laser gas analysis device compensates distortion of a laser beam and can place a detector depending on the wavelength used. A transmitter side process window unit consists of two wedge-shaped glass substrates that are positioned to have a space with an appropriate length along a laser propagation direction, and sends the laser beam from a transmitter unit to a measuring space. A receiver side process window unit is configured the same as the transmitter side process window unit, and sends the laser beam passed through the measuring space to a receiver unit. The outer surfaces of the two wedge-shaped glass substrates with respect to the space in between are placed to be parallel each other, and accordingly the inner surfaces are also parallel each other. The distance between the two wedge-shaped glass substrates in the laser propagation direction is determined so as to avoid optical interferences of the laser.

Claims

1. A laser gas analysis device including a transmitter unit sending a light emission from a tunable laser to a measuring space and a receiver unit detecting the laser transmitted through the measuring space, comprising: a transmitter side process window unit formed by two wedge-shaped glass substrates placed in a laser propagation direction in forming a specific space, and transmitting the laser beam from the transmitter unit to the measuring space; and a receiver side process window unit formed as well as the transmitter side process window unit, and transmitting the laser beam passed through the measuring space to the receiver unit.

2. The laser gas analysis device according to claim 1, wherein the two wedge-shaped substrates forming the prescribed space have outer surfaces of the two wedge-shaped glass substrates with respect to the specific space in between are placed to be parallel each other, and inner surfaces are also parallel each other.

3. The laser gas analysis device according to claim 1, further comprising: a unit for streaming or filling the space in the window units with a measuring gas species, and checking and adjusting the sensitivity.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0021] FIG. 1 is a diagram illustrating a basic principle in accordance with the present invention;

[0022] FIG. 2 is a diagram showing an optical path of a laser gas analysis device in accordance with the present invention;

[0023] FIG. 3 is a diagram showing the laser gas analysis device applying the present invention;

[0024] FIG. 4 is a diagram showing a conventional laser gas analysis device;

[0025] FIG. 5 is a diagram showing a functional overview of a laser gas analysis device; and

[0026] FIG. 6 shows an optical path of a conventional laser gas analysis device.

DESCRIPTION OF THE EMBODIMENT

[0027] <Principle>

[0028] FIG. 1 is a diagram that illustrates a basic principle of the present invention.

[0029] A parallel beam normally injected to a flat parallel glass substrate ω is transmitted to a normal direction with no diffraction, i.e., the transmitted beam is parallel and is on the same geometrical optical axis as the incident beam as shown in FIG. 1 (a) (1). When the flat parallel glass substrate ω is tilted with respect to the geometrical optical axis, the parallel beam is likewise transmitted as the parallel beam, while a small displacement from the geometrical optical axis occurs due to refraction depending on the tilt angle and the refractive index of the flat parallel glass substrate as shown in FIG. 1 (a) (2). This indicates that, even if the flat parallel glass substrate is divided at a given angle (the dashed line in FIG. 1 (a) (2), for example) into two wedge-shaped substrates ω.sub.1 and 107 .sub.2, the beam transmitted through two wedge-shaped substrates ω.sub.1 and ω.sub.2 is kept parallel as shown in FIG. 1 (b).

[0030] Furthermore, even though a space with a certain length is formed by the wedge-shaped glass substrate ω.sub.1 and ω.sub.2 toward a propagation direction, the beam transmitted through two wedge-shaped glass substrates ω.sub.1 and ω.sub.2 is consequently parallel to the incident beam and the displacement from the geometrical optical axis is also small as shown in FIG. 1 (c). That is, a distortion of the transmitted beam occurred against the injected parallel beam at the upstream side wedge-shaped glass substrate ω.sub.1 is compensated by the downstream side wedge-shaped glass substrate ω.sub.2 and the resultant beam transmitted two wedge-shaped glass substrates ω.sub.1 and ω.sub.2 is kept parallel.

[0031] The two wedge-shaped substrates ω.sub.1 and ω.sub.2 which form a space with a certain length along the propagation direction have two sets of the parallel surfaces. The outer surfaces α.sub.1 and α.sub.2 with respect to the space in between are placed to be parallel each other. Accordingly, the inner surfaces β.sub.1 and β.sub.2 with respect to the space in between are also parallel each other.

[0032] In the present invention, the transmitter side process window unit and the receiver side process window unit described hereafter are configured utilizing the above-mentioned two wedge-shaped substrates ω.sub.1 and ω.sub.2 placed with the specific space in between.

[0033] The length of the space along the laser propagation direction is determined so that the distortion occurred when passing through the upstream side wedge-shaped substrate ω.sub.1 to be effectively compensated by the downstream side wedge-shaped substrate ω.sub.2 as described above. The length of the space is also determined by taking the optical interference of the laser into account.

[0034] <Configuration>

[0035] FIG. 2 shows the example of an optical path of the laser gas analysis device in accordance with the present invention. FIG. 3 illustrates details of the laser gas analysis device in accordance with the present invention. The configuration is essentially the same as conventional arts wherein a transmitter unit 100 and a receiver unit 200 are installed at the opposite side of a process flue (a measuring space 30).

[0036] The light emission by the tunable laser element 111 in the transmitter unit 100 is parallelized by the collimation optics 112, and then transmits through the transmitter side process window unit 10. The transmitter side process window unit 10 consists of two wedge-shaped glass substrates ω.sub.11 and ω.sub.12 forming a space in between with an appropriate length as described above. The wedge-shaped glass substrate ω.sub.12 is the process window which separates the transmitter unit 100 and the transmitter side process window unit 10 from the measuring space 30.

[0037] The parallel beam passed through the transmitter side process window unit 10 propagates through the measuring space 30, and then enters the receiver side process window unit 20. The receiver side process window unit 20 consists of two wedge-shaped glass substrates ω.sub.21 and ω.sub.22 forming a space in between with an appropriate length. The wedge-shaped glass substrate ω.sub.21 is the process window.

[0038] The parallel beam transmitted through the receiver side process window unit 20 is injected to the collection optics 212 and falls on the photodetector 211.

[0039] In the laser gas analysis device configured as described above, the distortion of the beam occurred in the light passed through the upstream side wedge-shaped glass substrate ω.sub.11 is compensated by the downstream side wedge-shaped glass substrate ω.sub.12. Consequently, the parallel beam injected into the transmitter side process window unit 10 is transmitted as the parallel beam and enters the measuring space 30.

[0040] Then the parallel beam transmitted through measuring space 30 is injected to the receiver side process window unit 20. The distortion of the beam occurred again in the light beam passed through the upstream side wedge-shaped glass substrate ω.sub.21 is compensated by the downstream side wedge-shaped glass substrate ω.sub.22. As a result, the light beam parallelized by the collimation optics 112 in the transmitter unit and the beam injected into the collection optics 212 in the receiver unit is centered on the same geometrically defined optical axis.

[0041] By adopting the above configuration, the light beam is kept parallel, and the optical axis is identical regardless of the wavelength used whatever in visible, near-infrared or mid-infrared. According to this, the optical alignment procedures are simple and easy, and the adjusted optical alignment of the device is stable. Moreover, the normal incidence of the beam to the collection optics enables to design to place the photodetector at the focal point of the collection optics depending only on the wavelength used, and the power of the laser is not ruined.

[0042] In the above embodiment, the transmitter unit 100 and the transmitter side process window unit 10, and the receiver unit 200 and the receiver side process window unit 20 may be configured as one unit, respectively, otherwise may be separately configured. In case of separated units, it is possible to remove the transmitter unit 100 and the receiver unit 200 leaving the transmitter side process window unit 10 and the receiver side process window unit 20 at the installation flanges and to perform the maintenances of the transmitter unit 100 and the receiver unit 200 when necessary, even when the process is working.

[0043] In FIG. 3, also shown are tube fittings 131, 132 (231, 232) for respective an inlet and an outlet of the transmitter side (the receiver side) process window unit 10 (20) to introduce the gas mixture containing the gas species of interest with known concentration into the space formed by the two wedge-shaped glass substrates. Though the reference numerals 131 and 132 (231 and 232), the tube fittings, indicates the same object on the figure, the front side of the page is the inlet, and the back is the outlet, for example.

[0044] Owing to the above configuration, when the gas mixture containing the gas species of interest with known concentration is introduced into the space formed by two wedge-shaped glass substrates during the stop period of the measuring process, the checking of the device sensitivity or the scale adjustment without removing the device from the installation flanges can be performed according to the output signal of the lock-in amplifier. That is, the space can be utilized as a reference gas flow cell.

INDUSTRIAL APPLICABILITY

[0045] As mentioned so far, the optical alignment procedures of the device are to be simple and easy, and the adjusted optical alignment of the device is stable, compensating the distortions and displacements of the beam regardless of the wavelength used. It is not necessary to adjust the photodetector position at installation or maintenance. The maintenance work can be performed even when the measuring process is in operation. The checking of the sensitivity can be performed without removing the device from the process during the stop period of the measuring process. Therefore, the device in the present invention is quite beneficial for the practical applications.

REFERENCE SIGNS LIST

[0046] 10 transmitter side process window unit

[0047] 20 receiver side process window unit

[0048] 30 process flue (measuring space)

[0049] 100 transmitter unit

[0050] 110 transmitter side process window

[0051] 111 tunable laser element

[0052] 112 collimation optics

[0053] 210 receiver side process window

[0054] 211 photodetector

[0055] ωflat parallel glass substrate

[0056] ω.sub.1, ω.sub.2, ω.sub.11, ω.sub.12, ω.sub.21, ω.sub.22 wedge-shaped glass substrate

[0057] α.sub.1, α.sub.2 outer surface of two wedge-shaped glass substrates

[0058] β.sub.1, β.sub.2 inner surface of two wedge-shaped glass substrates