JPS6017706Y2 - Wavelength sweeping spectrometer using a tuning fork - Google Patents

Description

[Detailed explanation of the idea] [Field to which it belongs] The present invention relates to a spectrometer for use in a spectrometer.

There is a need for a spectrometer suitable for performing qualitative and quantitative analysis of gases or liquids.

In particular, there is a need for a spectrometer that has significantly improved sensitivity, accuracy, and stability compared to conventional spectrometers.

The present invention relates to a wavelength sweeping spectrometer that is required to realize a spectrometer that can be a useful measurement device for pollution-related projects that have been attracting attention in recent years. Another feature is that the slit is made to vibrate with a tuning fork at the exit.

[Background technology]

Since the spectrometer is the basic component of a spectrometer, first of all,
Let's consider the spectrometer.

It is known that the emission spectrum or absorption spectrum of a gas or liquid has a spectrum unique to the component atoms (molecules) contained therein.

Spectrometers that perform qualitative and quantitative analyzes of gases or liquids with high sensitivity based on their spectra include the higher-order derivative method.

In this higher-order derivative method, when an emission spectrum or an absorption spectrum is differentiated with respect to wavelength, the first-order derivative spectrum largely captures slight changes in the original spectrum before differentiation, and the spectral profile becomes sharp.
Furthermore, the second derivative spectrum obtained by differentiating this becomes even sharper, so qualitative and quantitative analysis of substances can be performed using these one method.
This is done using the first-order differential spectrum or the second-order differential spectrum.

However, this method requires an electronic computer to be attached to the spectrometer in order to obtain a differential spectrum, making it expensive and not widely used as it is.

In contrast to this method of obtaining a differential spectrum using an electronic computer, a method of obtaining a differential value of a spectrum in the vicinity of a certain wavelength by temporally applying sinusoidal wavelength modulation in the vicinity of that wavelength is simpler as an apparatus.

Here, it will be explained in a little more detail that by applying temporal sinusoidal wavelength modulation, the differential value of the spectrum in the vicinity of the wavelength can be obtained.

That is, the exit slit of the spectrometer is temporally waved sinusoidally to apply temporal sinusoidal modulation to the wavelength of light passing through the exit slit.

Enter the modulation amplitude at that time as a, the modulation angular frequency as ω, and the wavelength of the light passing through the exit slit when the exit slit is stopped.

, time is t, the wavelength of light passing through the exit slit can be expressed as in equation (1).

Input=λo11Slnωt (1)
On the other hand, enter the spectrum ■ (λ).

When the tiller is expanded in the vicinity of OI ■ (in) =,,i.

,, , 1 (n) (λo) (λ one person.

). It can be expressed as (2).

Substituting equation (1) into equation (2) yields.

In equation (4), the first term is a DC signal, and the second term s
The in term and the cos term are AC signals containing ωt.

In Equation (4), let m=1 and pay attention to the sine term and the cosine term. Equation (5) shows that the amplitude of the light intensity modulation signal with the angular frequency ω is pi.
) (xo), and from equation (6), the amplitude of the modulation signal with an angular frequency of 2ω is 1(2) (input).

).

Similarly, it can be understood from equation (4) that the amplitude of the modulation signal whose angular frequency is nω corresponds to the n-th derivative 1 (r'ゝ).

That is, when the center wavelength of the exit slit is modulated near the input 0, when its fundamental angular frequency is ω, when the amplitude of the AC signal whose angular frequency is nω is extracted, it becomes the input wavelength of the original spectrum.

Information corresponding to the nth derivative of is obtained.

The technology of spectroscopy using such wavelength modulation (which can also be called spectroscopy using higher-order derivative method) is old, dating back to 1968.

Perregaux, G., Ascarelli, Applied Optics Magazine
cs, vol, 7 p, 2Q31) i: There is an example described, and in 1973, J, D, Jobe disclosed the technology applied to the 11 photometer (U, S, Pat
.

3743425 C1, 356187).

However, all of them lacked specific technical disclosures, and could not be said to be technologies that could suddenly be used industrially.

The next section will discuss the prior art.

[Prior art and problems]

Various spectrometers based on this method have been proposed, and each of these spectrometers is characterized by the use of different techniques for applying wavelength modulation.

For example, there is a device that fixes the entrance and exit slits of a spectrometer, places a mirror inside the spectrometer, and modulates the center wavelength of the exit slit by shaking the mirror surface to wave the light beam. Since the oscillating mirror must be built inside the spectrometer, it is not possible to use conventional general-purpose spectrometers, and a new dedicated spectrometer must be designed, and a movable mirror must be installed inside the spectrometer. Because the parts are attached, adjustments at the manufacturing stage are complicated.

In addition, there is a device in which the entrance and exit slits of a spectrometer are fixed, and a transmission-type vibrating refraction plate inside the spectrometer is used to wave the light beam and modulate the center wavelength of the exit slit. In order to obtain a large amplitude, a thick refracting plate must be used, which results in a refracting plate with a large mass, making it difficult to vibrate the refracting plate.The basic drawback is that the refracting plate The problem is that a new chromatic aberration occurs in the spectrometer due to wavelength dispersion in the spectrometer.

In addition, there is a device that modulates the center wavelength of the exit slit by fixing the exit slit of the spectrometer and vibrating the entrance slit. Although it has some advantages, such as being easy to manufacture and being easily vibrated because the slit plate of the object to be vibrated is light, it also has the following disadvantages.

That is, the slit vibration device used in this device is a combination of parallel springs and a magnetic circuit, and vibrates at the natural frequency of the parallel springs.

In parallel springs, the free ends of two leaf springs are fixed relatively to each other, so the free ends of the springs are connected by a rigid body, the movable part of the spring is heavy, and the natural frequency of the parallel spring is at most The frequency is only 50Hz, and there are problems in frequency stability and amplitude stability.

There is also an example in which the entrance slit is driven by a so-called speaker, but if the amplitude is increased to meet the purpose of spectroscopic techniques, the upper limit of the vibration frequency is about 100 Hz, and in this case, the stability of the amplitude and the stability of the frequency are I have problems with sexuality,
There are also difficulties in mounting the entrance slit at the correct location of the entrance section of the spectrometer.

In addition, there is an example of a spectrometer in which the exit slit is vibrated, as disclosed in US Pat. No. 3,743,425 CI, 356-87° 1973.

However, the technical disclosure of this specification alone cannot address the following problems.

Below, I will explain the reason. We will discuss how the modulation frequency that modulates the center wavelength of the exit slit, the stability of the modulation frequency, and the stability of the modulation amplitude affect the sensitivity, accuracy, and stability of the spectrometer.

When a substance to be measured exists, when the center wavelength of the exit slit is modulated, a light intensity modulation signal is superimposed on the light incident on the photoelectric conversion element as shown in equation (5) or (6). Therefore, when the concentration of the substance to be measured is very low, this light intensity modulation signal is very small.

The optimal method for electrically detecting such a minute modulation signal is to use a so-called lock-in amplifier, which is different from a tuned amplifier and a synchronous detector.

This tuned amplifier is an amplifier tuned to the modulation signal frequency, and the higher the signal frequency is, the easier it is to construct a tuned amplifier with higher Q. Therefore, the higher the signal frequency is, the easier it is to improve the S/N.

In this way, increasing the modulation frequency can improve the S/N,
A highly sensitive spectrometer can be constructed.

However, since a high-Q tuning amplifier is used for this purpose, if the modulation frequency is not stable, it will deviate from the center frequency of the tuning amplifier, resulting in spectrometer drift.

Therefore, it is necessary that the modulation frequency has good stability.

Furthermore, since the modulation amplitude corresponds to a in equation (5) or (6), if the modulation amplitude a is unstable, the output will also be unstable, so the stability of the modulation amplitude is also important.

Regarding the modulation frequency, there is a trade-off with the photoelectric conversion element in addition to the above-mentioned trade-off with the tuned amplifier.

That is, photomultiplier tubes commonly used in the ultraviolet and visible regions produce a lot of noise at low frequencies, and the higher the frequency, the less noise there is.

Particularly, noise is significantly large below 200 Hz. Therefore, in order to perform signal processing with a good S/N ratio, it is preferable to apply modulation at a frequency of several hundred Hz or above, where the noise of the photomultiplier tube is small.

However, spectrometers that use conventional spectrometers that swing the entrance slit use parallel springs or speakers to swing the slit, making it difficult to maintain frequency, frequency stability, and amplitude stability. Because of this, conventional spectrometers had problems with sensitivity, accuracy, and stability.

Furthermore, regarding the device that swings the exit slit, no specific disclosure of a technique for solving the above-mentioned problem was found.

[Purpose of this invention]

The purpose of the present invention is to provide a wavelength sweeping spectrometer that eliminates the drawbacks of the prior art and realizes a spectrometer using a tuning fork that has good sensitivity, precision, and stability, and is easy to manufacture. It is.

[Summary of configuration]

Distantly related to this purpose, it is characterized by the following structure.

In other words, (a) By vibrating the entrance slit or the exit slit and applying wavelength modulation to the light passing through the exit slit, the object to be vibrated is made into a light plate-like body with slits, making it easy to vibrate the object to be vibrated. Make it.

(b) By making the object to be vibrated a light plate-like body that can be easily vibrated, it is possible to use a tuning fork as a vibration source for a slit.

(c) By using a tuning fork as a slit vibration source, it is possible to obtain temporally sinusoidal slit vibration, that is, it is possible to apply temporally sinusoidal wavelength modulation.

(d) By supporting the central part of a U-shape (including ■-shape and square-shape) or straight bar shape, a tuning fork with two vibrating free ends is constructed.

(e) By using a tuning fork with two free ends for vibration, stable slit vibration with a high Q can be obtained.

(f) By using a tuning fork with two vibrating free ends, sufficient vibration amplitude can be obtained with a weak driving force. By sandwiching and supporting the plate-like body with two supports with tooth-shaped edges at the combined center of gravity of the plate-like body and the straight rod-shaped tuning fork with the body attached to one free end, or by supporting the plate-like body with the body attached to one free end. By attaching it to one end and supporting the center by attaching a balancer with a mass substantially equal to that of the plate to the other free end, a high-Q tuning fork with a slightly lower natural frequency than the original straight rod-shaped tuning fork is created. Configure the vibrator.

(H) When using a straight rod-shaped tuning fork, the center of gravity of the plate-shaped body and the center of gravity of the balancer are substantially located on the central axis of the rod, and a vibrator that vibrates in a single mode with high Q is configured. .

(IJ) When using a U-shaped tuning fork, a plate is attached to the free end of one leg via a holder, and a mass substantially equal to the combined mass of the plate and the holder is attached to the free end of the other leg. By installing a mass balancer, a high Q vibrator is constructed.

(J) When using a U-shaped tuning fork, the combined center of gravity of the plate and holder and the center of gravity of the balancer should be located within a plane of symmetry that includes both legs of the U-shaped tuning fork, and substantially relative to the center line of the tuning fork. By arranging them symmetrically, a vibrator with a high Q and a single vibration mode is constructed.

(l) By making the tuning fork from a magnetic material, it is possible to drive the vibrator with magnetic force.In other words, an alternating current is passed through the driving electromagnetic head, which is constructed by winding a coil around the core. This makes it possible to generate an alternating magnetic field and drive the vibrator with this alternating magnetic field.

(w) By constructing a slit vibration sinking device equipped with a driving electromagnetic head on one leg of the tuning fork, and by passing a stable alternating current with a frequency equal to the natural frequency of the vibrator to the driving electromagnetic head, The modulation frequency is stabilized so that the vibrator has stable natural vibrations, allowing a spectrometer with stable output.

(W) By passing an alternating current with a stable effective value through the driving electromagnetic head, a stable alternating magnetic field is generated so that the vibrator vibrates with a stable amplitude, that is, the amplitude of wavelength modulation is stabilized, Enables a spectrometer with stable output.

(Force) By configuring a vibrator composed of a tuning fork in the main part of the slit vibrator, it is possible to obtain high-frequency slit vibration, that is, to increase the modulation frequency, and it is possible to obtain high-frequency spectroscopy with high sensitivity and precision. enable measurement.

(Y) The wavelength modulation device (this invention This slit vibration device) simplifies manufacturing, including installation and adjustment.

[First example]

The first embodiment will be described below with reference to the drawings.

FIG. 1 shows the constituent countries of a first embodiment of the present invention.

In the same figure, the light emitted from the light source 1 is made into a parallel beam by the collimator lens 5, and then is inserted into the absorption cell 10, which has the function of collecting and introducing the medium to be measured to generate an absorption spectrum. incident from

This incident parallel light beam gradually diverges as it propagates, so it is reflected by the concave mirror 21 and reflected by the plane mirror 22.
The parallel light flux is returned to be a parallel light flux similar to the original parallel light flux on the surface of , and this parallel light flux is further reflected by the plane mirror 22.

After repeating this kind of reflection many times, the exit window 1 of the absorption cell
A parallel beam of light is emitted from 2.

Repeated reflection optical device 2 provided inside the absorption cell 10
0, a mirror (such as 2L22) is arranged so that the optical axes of the light beams that are repeatedly reflected (reciprocated) within the mirror are all in the same plane.

The absorption cell 10 is a cylinder with a rectangular cross section in order to minimize its capacity.

The parallel light flux emitted from the exit window 12 of the absorption cell 10 enters the interior of the spectrometer 40 where it is focused by the collector lens 30 onto the fixed entrance slit 41 of the spectrometer body 40, and is then focused by the dispersion mechanism 42 of the spectrometer 40. Wavelength-dispersed and monochromatic light passes through the exit slit 55 that is directed at the plate-like body 50 to form a head-shaped photomultiplier tube 80 with a substantially uniform light-receiving surface.
incident on the light receiving surface.

The plate-shaped body 50 is attached to a slit moving device 60,
The slit vibrating device 60 uses a tuning fork as a driving mechanism, which applies vibration to the plate-shaped body 50, vibrates the exit slit 55, and modulates the wavelength of the monochromatic light passing through the exit slit 55.

At this time, the atmosphere inside the absorption cell 10 is exhausted by an exhaust pump (not shown) connected to the exhaust port 14 of the absorption cell 10 to lower the air pressure inside the absorption cell 10, and new air ( If the sampled air contains an air pollutant such as SO2 gas (substance to be measured), the SO2 of the plate-shaped body 50
The spectrum produced by the absorption of light by the gas is imaged.

That is, a light and dark pattern parallel to the exit slit 55 is generated in the lateral direction of the plate-shaped body 0 (X direction in FIG. 1).

The dark portion corresponds to absorption of SO2 gas.

The horizontal direction (X direction in the figure) of the plate-shaped body 50 corresponds to the wavelength input of the light, and the bright and dark pattern is the intensity distribution of the light, so the spectrum generated by absorption of SO□ gas is plotted as the wavelength input on the horizontal axis. If the light intensity (■) is plotted on the vertical axis, the result will be as shown in FIG. 2.

In the same figure, the position coordinates X of the exit slit 55 are shown in the X direction of FIG. 1 in correspondence with wavelength import.

In the figure, the slit position when the exit slit 55 is stopped is indicated, and the amplitude peaks of the exit slit 55 are indicated by Xl and X2.

As shown in the figure, the position formula when the exit slit 55 is stopped is wavelength A.
, (299nm), and the amplitude peaks x1 and ~ of the exit slit 55 correspond to the input wavelengths, (298nm) and λ2 (30onm).
When the exit slit 55 is vibrated to correspond to the angular frequency ω of the exit slit 55, a light intensity modulation with a frequency 2ω, which is twice the angular frequency ω of the exit slit 55, is applied, and this light intensity modulation signal is converted into the received light signal shown in FIG. A head-shaped photomultiplier tube 80 with a substantially uniform surface performs photoelectric conversion, and an output corresponding to the degree of modulation of the modulation signal with a frequency of 2ω (an output corresponding to the second differential value of the spectrum) is sent to an electric processing system 85. The output is generated in the processing unit 90 within the unit, and the output is displayed on the output display unit 96.

When shaking the exit slit as in this first embodiment,
Since the light flux passing through the exit slit naturally sways, a photomultiplier tube with a lattice-shaped photomultiplier tube with a non-uniform light-receiving area cannot be used, and a photomultiplier tube with a shaped head with a uniform light-receiving surface as in the first embodiment is not used. need to use it.

Next, the slit vibration device 60 used in the first embodiment of the present invention
will be explained in detail.

In Figure 3, a U-shaped tuning fork 6 with a high natural frequency and a high Q
1 is used as a vibration source for the exit slit 55.

A plate-shaped body 50 with an outlet slit 55 is attached to the free end of one leg of this U-shaped tuning fork 61 via a holder 63, and a balancer 62 for maintaining the balance of the tuning fork is attached to the free end of the other leg. A very high Q vibrator is installed.

To explain in more detail, in order to configure a high Q vibrator, the mass of the balancer 62 is made substantially equal to the combined mass of the plate-shaped body 50 and the holder 63,
2 and the composite center of gravity of the plate-shaped body 50 and the holder 63 substantially exist within the plane of symmetry of the tuning fork that includes both legs of the U-shaped tuning fork, and the respective centers of gravity are substantially located with respect to the center line of the U-shape. It is arranged symmetrically.

In order to drive this vibrator with magnetic force, the U-shaped tuning fork 61 is made of a magnetic material.

A pickup electromagnetic head 64 for picking up the natural vibration of this vibrator is placed on one leg of the U-shaped tuning fork with an appropriate gap therebetween, and a driving electromagnetic head 65 is provided on the other leg.

An electro-mechanical system includes a drive circuit 70 that amplifies the alternating current picked up by the pickup electromagnetic head 64 and generates a constant output driving alternating current, the pickup electromagnetic head 64, the drive electromagnetic head 65, and the vibrator. It consists of an oscillation device.

Both electromagnetic heads 64 and 65 are connected to a core 68.68' and a coil 69.69' wound around the core 68.68'. Built-in constant current generation circuit 71
A constant current is always supplied from the electromagnetic head 64, and the electromagnetic head 64 becomes a magnet.

Therefore, when the tuning fork 61 vibrates even slightly and the gap between the core 68 of the electromagnetic head 64 and the leg of the tuning fork 61 changes, the magnetic resistance changes, and therefore the density of the magnetic lines of force running through the core 68 changes, causing the coil 69 to vibrate. An alternating current is induced in response to the vibrations.

This induced alternating current is amplified by an amplifier 73 built into the drive circuit 70, and a drive voltage is applied to the drive electromagnetic head through a drive voltage adjustment circuit 74 for making the vibration of the tuning fork 61 a constant amplitude.

In order to keep the amplitude of the tuning fork 61 constant, the picked-up alternating current is amplified by an amplifier 75, and this alternating current is passed through a full-wave rectifier circuit 76 and a low-pass filter 77 to obtain a signal corresponding to the absolute value of the picked-up alternating current. The drive voltage adjustment circuit 74 automatically adjusts the drive voltage in such a manner that an output is generated, and as this output increases, the drive voltage decreases.

In this way, since the vibrator is vibrated at the natural frequency of the vibrator and by a drive circuit that automatically adjusts the drive voltage, stable vibration with a high Q amplitude can be obtained as is.

According to the experimental results using the slit vibrating device explained above,
Very stable with an amplitude of about 1 and a frequency of about 400H2.
Furthermore, we were able to obtain accurate sine wave vibrations.

Next, the electrical processing system will be explained in detail with reference to FIG.

In the figure, an electrical output signal from a head-shaped photomultiplier tube 80 is amplified by a preamplifier 120 built in a processing section 90 in an electrical processing system 85, and after removing a DC component by a capacitor 121, a bandpass filter 122 is used. An alternating current signal with a frequency 2ω, which is twice the frequency ω of the exit slit, is extracted, further amplified by an amplifier 123, and input to a synchronous switch circuit 124.

This synchronous switch circuit 124 is turned on when the modulation signal of frequency 2ω is a positive half-wave, and turned off when it is a negative half-wave, thereby functioning to half-wave rectify the signal.

Furthermore, when the polarity of the output of the amplifier 123 is inverted by the polarity inverting circuit 125, the negative half wave of the output signal of the amplifier 123 becomes a positive half wave, so this positive half wave is transferred to the synchronous switch circuit 125.
', and is combined with the output signal of the synchronous switch circuit 124 at the entrance of the low-pass filter 130, thereby full-wave rectifying the output signal of the amplifier 123.

The synchronization signal of the synchronization switch circuits 124 and 124' is
The drive signal of frequency ω from the drive circuit 70 is passed through a phase shifter 110 for phase adjustment,
ω signal, and further used a frequency divider 112 to create two rectangular waves with a frequency of 2ω whose phases were shifted by 180°.

The aforementioned full-wave rectified signal is smoothed by a low-pass filter 130 and then enters the numerator of a divider 135.

On the other hand, the DC component of the output of the preamplifier 120 is amplified by the DC amplifier 131 and then input into the denominator of the divider 135.

In this way, the output of the divider 135 is set to a value corresponding to the degree of modulation of the modulation signal that does not depend on the light source intensity, etc., and this is displayed on the output display 96.

At this time, if the display value of the output display and the gas concentration to be measured (SO2 gas concentration in the embodiment) are calibrated in advance, the output can be displayed in accordance with the gas concentration.

Therefore, if fresh air is continuously collected into the absorption cell by continuously exhausting the air inside the absorption cell, the concentration of SO2 gas in the air can be continuously measured.

In the description of the first embodiment, the gas to be measured was SO2 gas, but any substance that has absorption at wavelengths longer than about 2001 m and whose absorption spectrum has a relatively sharp structure can be measured.

Therefore, by using an ordinary spectrometer 40, which is a wavelength scanning spectrometer and can stop scanning at any wavelength, it is possible to measure the concentration of a predetermined substance in accordance with a predetermined wavelength.

[Second to Ninth Embodiments]

Next, a second embodiment will be described.

As explained in the first embodiment, if necessary, the spectrometer 4
0 is a wavelength scanning type spectrometer, and the wavelength scanning mechanism that performs wavelength scanning is equipped with a potentiometer, and a normal spectrometer is configured to generate a DC output according to the wavelength scanning. The output corresponding to the scan is output from the X-Y recorder.
When the measurement output of the processing section 90 of the electrical processing system is placed on the Y axis and the wavelength scanning mechanism of the spectrometer 40 continuously scans the wavelength, the atmospheric absorption spectrum is second-order differentiated on the XY recorder. A second derivative spectrum is obtained.

Qualitative and quantitative analysis of pollutant gases contained in small amounts in the atmosphere can be performed from this second-order differential spectrum.

Next, a third embodiment will be described.

In the first embodiment and the second embodiment, the absorption cell 10 is used as the light source 1.
Although it is arranged between the absorption cell and the entrance slit 41 of the spectrometer, it may be arranged between the absorption cell, the exit slit 55 of the spectrometer, and the photomultiplier tube 80.

With this arrangement, when the exit slit is swung, the light beam repeatedly sways within the reflection optical system, so the light intensity modulation signal may be affected by slight dirt on the mirror of the repeating reflection optical system or the peripheral edge of the light beam deviating from the mirror. It is better to shake the inlet slit without shaking the exit slit, as this is undesirable as it generates a zero hour signal.

Such an arrangement is shown in FIG.

In the figure, 41' is a vibration entrance slit of the spectrometer 40 carved in a plate-like body 50', and 55' is a fixed exit slit of the spectrometer 40.

The plate-shaped body 50' is attached to a slit vibrating device 60, and the slit vibrating device 60 vibrates the entrance slit 41' to modulate the wavelength of light passing through the fixed exit slit 55'.

Also, in this case, the exit slit 55' is fixed,
Since the light beam passing through the exit slit 55' does not waver, the photomultiplier tube 80' does not have to be a head window type photomultiplier tube, and can be a commonly used photomultiplier tube having a grid line-shaped light receiving section. It's okay.

Next, a fourth embodiment will be described.

In the embodiment shown in FIG. 3, the pickup head is composed of an electromagnetic head, but it may also be constructed like a photocoupler in which a light emitting diode and a photodiode are opposed to each other.

Its configuration is shown in FIG. A pickup head 64' for picking up vibrations of the tuning fork 61 is composed of a light emitting diode 642 and a photodiode 645.

At this time, when the tuning fork vibrates, the cross section that blocks the light beam emitted from the light emitting diode changes slightly.
The amount of light received by the photodiode changes depending on the tuning fork vibration.

In this way, tuning fork vibrations can be picked up.

Next, a fifth embodiment is shown in FIG. 7 and will be explained with reference to the same figure.

70' is a drive circuit, which is separated from a stable oscillation circuit 72 that generates a sine wave or a rectangular wave with a frequency equal to the natural frequency of the tuning fork 61, and a stable amplifier 79 that amplifies its output; ' causes a stable alternating current with an effective value of a stable frequency equal to the natural frequency of the vibrator to flow through the coil 69' of the driving electromagnetic head 65 of the slit vibrator, thereby driving the slit vibrator at the natural frequency.

Next, a sixth embodiment will be described.

In the first embodiment, a U-shaped tuning fork was used as the vibration source of the slit, but a straight rod-shaped tuning fork as shown in FIG. 8 may also be used.

In the same figure, a tuning fork support 6 having a tooth-shaped edge at the center of gravity with a plate member 50 attached to a linear rod-shaped tuning fork 61'.
6 and 66' constitute a high Q vibrator.

At this time, the center of gravity of the plate-shaped body 50 was placed substantially on the central axis of the rod.

If this is not done, the Q will drop and the vibration mode will become multi-mode, which is not desirable.

Furthermore, although FIGS. 3 and 8 depict tuning forks whose legs have a rectangular cross section, the cross section may of course be circular or oval.

The U-shaped tuning fork or straight rod-shaped tuning fork as described above, which has two vibrating free ends by supporting the center thereof, has a very high Q and requires relatively little driving force.

However, even with a tuning fork in the form of a straight rod, like a cantilever beam, where there is only one free end for vibration and one fixed end, the vibrations of the tuning fork are transmitted from the fixed end to the spectrometer to which the tuning fork is attached. The energy of the vibrations escapes towards the spectrometer.

Therefore, it is not possible to efficiently drive a tuning fork that has only one free end of vibration, and vibrations are constantly applied to the spectrometer body, causing the optical axis inside the spectrometer to shift. It is not preferable to use a tuning fork that has only one free end of such vibration.

Next, a seventh embodiment will be explained.

In the first embodiment, the electrical processing system 85 transmits a light intensity modulation signal having a frequency 2ω, which is twice the angular frequency ω of the exit slit 55.
The second derivative of the extracted absorption spectrum was measured with
It is also possible to extract the light intensity modulation signal of frequency ω by the electrical processing system 85 and measure the first-order differential value.

In this case, in the processing section 90, the bandpass filter 12
The first differential value can be measured by setting the center frequency of .omega.2 to .omega. and further removing the multiplier circuit 111 in the circuit that generates the synchronizing signal.

Next, it is effective to modify the repeating reflection optical device 20 built into the absorption cell used in the first embodiment as follows (eighth embodiment).

In other words, in order for all the optical axes of the light beams that are repeatedly reflected within the repeating reflection optical device to occupy a three-dimensional space, a plurality of mirrors are divided into pieces that are approximately the same size as the thickness of the light beams. The arranged repeating reflection optical device can be a cylindrical absorption cell, which has a smaller capacity and is easier to manufacture than a rectangular cylindrical absorption cell.

Next, a ninth embodiment will be described.

In the first embodiment, the plate-like body 50 is made of phosphor bronze, and the exit slit 55 is formed by photo-etching, but the plate-like body does not necessarily have to be made of metal, and a photosensitive film, a glass sensitive plate, etc. It is also possible to develop the entire surrounding area to be opaque, leaving a thin transparent area that transmits light.It is also possible to develop the entire surrounding area to be opaque, leaving a thin transparent area through a normal transparent film or glass plate. be.

〔effect〕

As explained above, the present invention solves the drawbacks of the conventional spectrometer based on the high-order derivative method by vibrating the entrance or exit slit using a tuning fork, and changing the wavelength of the emitted light into a sinusoidal wave over time. By realizing a swept spectrometer, we have made the following improvements and obtained various effects.

That is, (a) since the entrance slit or the exit slit is vibrated and the wavelength modulation is applied to the light passing through the exit slit, the object to be vibrated can be made into a light plate-like body;
It was possible to make the vibrating object vibrate.

(b) Since the object to be vibrated was made into a light plate-like body so that it could vibrate easily, it became possible to use a tuning fork as a vibration source for the slit.

(c) Since a tuning fork was used as the vibration source of the slit,
We were able to obtain temporally sinusoidal slit vibration, and were able to apply temporally sinusoidal wavelength modulation.

(d) By using a tuning fork with two free ends for vibration, supported by a U-shaped or straight rod-shaped center, it was possible to obtain slit vibration with a high Q.

(E) Since we used a tuning fork with two vibrating free ends,
We were able to obtain sufficient vibration amplitude with a weak driving force.

(f) Since we used a tuning fork with two vibrating free ends,
It has become possible to create a stable spectrometer that does not transmit vibrations to the spectrometer body and that does not cause optical axis deviation due to tuning fork vibration.

(g) When using a linear rod-shaped tuning fork, the center of gravity with the plate-shaped member attached was supported by being sandwiched between two tooth-shaped edges, making it possible to construct a vibrator with a high Q.

(H) When using a tuning fork in the form of a straight rod, the center of gravity of the plate-shaped body was placed substantially on the central axis of the rod, so a vibrator with a high Q value and vibrating in a single mode could be constructed.

('J) When using a U-shaped tuning fork, a plate is attached to the free end of one leg via a holder, and a plate is attached to the free end of the other leg, substantially equal to the combined mass of the plate and the holder. Since a balancer of equal mass was installed, a vibrator with a high Q could be constructed.

(J) When using a U-shaped tuning fork, the combined center of gravity of the plate and holder and the center of gravity of the balancer should be located within a plane of symmetry that includes both legs of the U-shaped tuning fork, and substantially relative to the center line of the tuning fork. Because they were arranged symmetrically, it was possible to construct a vibrator with a high Q and a single vibration mode.

(l) Since the tuning fork was made of magnetic material and equipped with an electromagnetic head to drive the tuning fork, it was possible to vibrate the vibrator with alternating current.

(w) Using a drive circuit that generates an alternating current with a stable frequency equal to the natural frequency of the vibrator, this alternating current is passed through the electromagnetic head for driving the tuning fork, so that the vibrator produces stable natural vibration. We were able to.

In other words, the modulation frequency can be stabilized, and as a result, a spectrometer, and eventually a spectrometer, with stable output has become possible.

(W) Since a drive circuit in which the drive voltage is automatically adjusted is used, the vibration amplitude of the vibrator can be stabilized, that is, the amplitude of wavelength modulation can be stabilized, and as a result, the output can be stabilized. A spectrometer, and eventually a spectrometer, became possible.

(Force) Since the main part of the slit vibrating device uses a vibrator composed of a tuning fork, it is possible to obtain high-frequency slit vibration, that is, the fluctuation frequency can be increased, resulting in improved sensitivity and accuracy. This made it possible to create a good spectrometer and eventually a spectrometer.

(Yo) Because the slit was vibrated and wavelength modulated,
The installation and adjustment of the wavelength modulation device (in this invention, the slit vibrator) is easy, as it is only necessary to attach the slit vibrator to the spectrometer from the outside of the spectrometer so that the slit is in the specified position. became.

When a spectrometer constructed using a wavelength sweeping spectrometer using a tuning fork according to the present invention is used to measure pollutants in the atmosphere, such as SO2 gas, NO gas, NO2 gas, 03 gas, or various volatile substances, be effective.

To explain in more detail, when the SO2 gas concentration in the atmosphere is measured using the spectrometer described in the first embodiment of the present invention with a measurement target wavelength of 3001 m, the detection sensitivity is approximately 3 ppb and the measurement accuracy is ±1.5 ppb. The long-term stability over one week was also measurable at 3 ppb or less.

Furthermore, when measuring SO2 gas with the measurement target wavelength at 211nm, a detection sensitivity of less than Ippb can be obtained, but at 211nm
In the wavelength region as short as m, the absorption of volatile substances contained in the atmosphere is strong, so the interference effect of other substances on SO2 measurement is large and the measurement accuracy is poor, which is not preferable.

With conventional spectrometers, 300 nm is the wavelength to be measured, which is approximately 2
Some have SO2 gas detection sensitivity of 4Ppb,
It is common for SO2 gas contamination concentrations in the atmosphere to be less than 20 ppb, and such low concentrations could not be measured with any conventional spectrometer.

However, it can be sufficiently measured using a spectrometer constructed using a wavelength sweeping spectrometer using a tuning fork according to the present invention.
This spectrometer is very effective when used in the field of pollution measurement, especially environmental measurement.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a first embodiment of a spectrometer constructed using the wavelength sweeping spectrometer of the present invention. FIG. 2 is a diagram showing the spectrum of passing light that has been absorbed by SO2 gas, and is also an explanatory diagram of the present invention showing the relationship between the slit position and wavelength in the output section of the spectrometer. FIG. 3 is a configuration diagram showing the slit vibration device employed in the first embodiment. FIG. 4 is a block diagram of the electrical processing system used in the first embodiment. FIG. 5 is a diagram showing a third embodiment of the present invention. FIG. 6 and FIG. 7 are diagrams showing a fourth embodiment and a fifth embodiment of the present invention. FIG. 8 is a block diagram of a slit vibrating device using a linear rod-shaped tuning fork, which is a sixth embodiment of the present invention. 1: Light source, 40: Spectrometer body, 41: Entrance slit, 4
2: Dispersion mechanism of spectrometer 40, 50: Plate-shaped body, 55: Exit slit formed in plate-shaped body 50, 60 Nislit vibrator, 61: U-shaped tuning fork, 61': Straight rod-shaped tuning fork, 62
: balancer, 63: holder, 64: electromagnetic head for pickup, 65: electromagnetic head for drive, 65'2 electromagnetic head for forced drive, 70: drive circuit, 70'2 drive circuit for forced drive, 80: head Part window layer photomultiplier tube, 85
: Electrical processing system, 90: Processing section, 96: Output display section.

Claims (5)

[Scope of utility model registration request] (1) A spectrometer including an entrance slit and an exit slit through which a light beam having a spectral structure passes, and a slit vibrator that vibrates either the entrance slit or the exit slit, and the spectrum is made to correspond to wavelengths. In a wavelength sweeping spectrometer that emits light over time, the inlet slit or the outlet slit vibrated by the slit vibrating device is formed in a plate-like body, and the slit vibrating device has a tuning fork with two legs. , a holder provided for attaching the plate-like body to the free end of one leg of the tuning fork, a combined mass of the plate-like body and the holder attached to the free end of the other leg, and substantially a balancer having the same mass, the combined center of gravity of the plate-shaped body and the holder and the center of gravity of the balancer substantially lie within a plane of symmetry of the tuning fork that includes both legs of the tuning fork, and the plane of symmetry A wavelength sweeping spectrometer using a tuning fork, characterized in that the tuning fork is arranged substantially symmetrically with respect to a center line of the tuning fork. (2) Utility model registration claim 1, characterized in that the tuning fork is a U-shaped tuning fork and is made of a magnetic material.
Wavelength sweeping spectrometer using the tuning fork described in Section 1. (3) The slit vibrating device includes a U-shaped tuning fork and an electromagnetic head for forced driving placed on one leg of the tuning fork, and the tuning fork is caused to vibrate at the natural frequency of the tuning fork by the electromagnetic head. A wavelength sweeping spectrometer using a tuning fork according to claim 1, characterized in that: (4) The slit vibrating device includes a U-shaped tuning fork, a pickup electromagnetic head placed on one leg of the tuning fork, and a driving electromagnetic head placed on the other leg, and the tuning fork is driven by both heads. A wavelength sweeping spectrometer using a tuning fork according to claim 1, characterized in that the tuning fork vibrates at its natural frequency. (5) A wavelength sweeping spectrometer using a tuning fork according to claim 1, wherein the tuning fork is a wired rod-like tuning fork.