JPH0843204A - Multiplex-frequency spectrometer - Google Patents

Abstract

PURPOSE: To perform a highly sensitive spectrometry for a rather opaque sample by positioning a light detecting device in order to detect the scattered light within a sample space. CONSTITUTION: A two-multiple frequency converter 4 is assembled by connecting a RF generator 6 operated at 1GHz and a signal generator 7 operated at 10MHz to a mixer 5, and the injection current is modulated at two adjacent FR frequencies. A spot 13 incident on a sample 10 scans the surface of the sample 10, and a mirror 12 functions as a sweeping means. An optical sensor 20 sensitive to infrared lights within the wavelength range of a semiconductor laser 1 is set up so as to shield the light scattered in backward scattering direction, and an aperture 30 changes the narrow range of scattering angle of the light collected by the optical sensor 20. A light detecting device 25 detects the light scattered within the sample 10, and supplies a monitor signal to a signal processing unit 26.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The invention relates to an illumination system having a light source for illuminating at least part of a sample space with light having at least two frequencies, and an optical sensor for detecting light leaving said sample. A frequency sensitive photodetector, an optical system for imaging the output surface of the illumination system onto the photosensor through a sample in the sample space, and a signal for processing an electronic detection signal from the photosensor. A multiple frequency modulation spectrometer having a processing system.

[0002]

2. Description of the Related Art This type of device is called "Frequency modulati
on spectroscopy at 1.3 μm usingInGaAsP lasers: a
prototype field instrument for atmospheric chemist
ry research ”by TJ Johnson Applied Optics 30 (1
991) pp. 407-413.

The known device comprises a long wavelength (1.3 μm) semiconductor laser whose output light is simultaneously frequency modulated at two adjacent RF frequencies, ie 461 ± 1.5 MHz. This frequency modulation is actually done by modulation of the injection current supplied to the laser. The frequency-modulated light passes through a sample space having the shape of a multiple reflection (white) cell. The light exiting the white cell is detected by the photodiode and high frequency components from the detection signal of the photodiode are filtered by the low pass filter. Then, two adjacent Rs included in the detection signal are detected.
The low frequency beat signal of the F signal is generated by a mixer that beats the output signal of the low pass filter to a signal having a stable frequency equal to the separation of the RF modulation frequency of the output light of the semiconductor laser, ie 3 MHz. The amplitude of the beat signal of the adjacent RF signals represents the difference between the optical densities of the optical frequencies on one side of the high frequency modulation sidebands of the laser light. That is, the amplitude of the beat signal of the adjacent RF signal exceeds the frequency of the laser light,
That is, it represents the difference between the absorption in the sample at an average modulation frequency above the center optical carrier frequency of the semiconductor laser and the absorption at an average modulation frequency below the center carrier frequency when no modulation is applied. Therefore, the amplitude of the beat signal provides information on the absorption spectrum of the sample material. Since the beat signal has a frequency equal to the difference between the frequencies of the adjacent sidebands or 3 MHz,
The response speed of the detector need only be on the order of 1 or a few MHz. The detection can be performed at such a low frequency that very high sensitivity can be achieved,
Absorption and / or absorption by a very small amount of the sample material
Alternatively, a very weak absorption by the sample material can be measured.

The known device is designed for studies in atmospheric chemistry. The known device requires light to travel through the sample space along a very long path length in order to be able to measure small collections of trace gases. The cited document describes a path length of 200 m formed by multiple reflections. When the sample scatters light strongly, the light can hardly travel straight along such long path lengths. When the sample placed in the sample space is not sufficiently transparent, almost no light exits the white cell and no beat signal with a significant signal-to-noise ratio can be detected. The sample may thus be opaque and the intensity of the transmitted light may even be very low, so that it remains below the detection limit of the photodiode. Therefore, the known device is not suitable for employing a spectrometer on samples which are to some extent opaque and scattered by the light emitted by the laser. In particular, the known device cannot employ a spectrometer on human or animal tissue for examining the tissue due to the presence of lesions such as cancer and for distinguishing malignant from benign tumors.

[0005]

OBJECTS AND SUMMARY OF THE INVENTION It is an object of the invention, inter alia, to provide a highly sensitive spectrometer for performing spectroscopic measurements on samples that are highly opaque due to scattering by the light emitted by the light source of the spectrometer. That is.

To this end, the spectrometer according to the invention is characterized in that a photo-detecting device is arranged for detecting the light scattered in the sample space.

When the sample is substantially opaque to the incident light from the light source, the intensity of the light scattered by the sample is much greater than the intensity of the light transmitted through the sample. Therefore, positioning of the photosensor to detect scattered light allows formation of a large detection signal. Furthermore, the photo-detecting device is sensitive to different frequency components of the detection signal and is arranged to form a signal representing the difference between the frequency components of said detection signal. For example, a frequency sensitive photodetection system comprises an electronic circuit that is sensitive to frequency components of an electronic detection signal and is arranged to form a beat signal at a low frequency of the frequency component of the detection signal, eg, an RF frequency. Good.

The multi-frequency spectrometer according to the invention is particularly suitable for non-intrusive real-time medical examinations.

An embodiment of a multi-frequency spectrometer according to the invention in which an illumination system is arranged to illuminate a portion of the sample space with a narrow light beam is provided in which a light sensor is provided on the sample with the narrow light beam from the illumination system. It is characterized in that it is positioned to receive the light scattered by the sample along a direction different from the incident direction.

The sample is selectively and locally illuminated by a relatively narrow incident beam having a cross section substantially smaller than the size of the sample. When the incident light is scattered at scattering centers within the sample, most scattered light exits the sample at a scattering angle with respect to the incident light. The scattering angle is approximately the angle of the light scattered in the central ray of the narrow beam, because
This is because the incident light beam is narrow. Positioning the photosensor at a non-straight angle to the incident light beam, i.e., not along the forward propagation direction, achieves that the photosensor blocks light scattered into the sample over a selected range of scattering angles. To do. The selected angle is determined by the characteristics received and the positioning of the photosensor.

It is also an object of the present invention to provide an apparatus for implementing the high sensitivity imaging spectrometer of the above object.

To this end, a preferred embodiment of the spectrometer according to the invention is characterized in that the optical system comprises confocal optics.

Light that enters the sample at the illuminated spot may exit the sample from a location outside the illuminated spot because scattering occurs within the sample. The confocal optics primarily illuminate the surface of the sample or a well defined sample portion below the surface, providing that light from only the sample portion is sharply imaged onto the photosensor. Another improvement is achieved in that the optical system comprises a spatial filter between the sample and the photodetection system. The spatial filter is positioned to prevent light leaving the sample portion outside the sample portion from reaching the photosensor. Within the confocal arrangement, the light from the sample portion is collected at an intermediate focus. A simple pinhole located at an intermediate focus in the confocal optical arrangement functions as a spatial filter, which means that light leaving the sample from parts other than the illuminated sample part reaches the photosensor. Avoid almost completely. In this way, crosstalk between light leaving from different locations on or in the sample is substantially avoided. If the pinhole is made narrower, the size of the sample portion where scattered light may reach the photosensor is made smaller and the spatial resolution of the spectrometer is increased.

Another preferred embodiment of the spectrometer according to the invention is characterized in that the optical system comprises sweeping means for sweeping the light beam from the illumination system towards at least part of the sample.

The incident light beam is directed onto different points of the sample. That is, the incident light beam is swept across the surface of the sample. As a result, the light continuously captured by the photosensor during the sweep is
Scattered at various scattering centers within the sample. Differences in the scattering centers cause differences in the intensity of the light scattered by each of these. For each point of incidence, a detection signal is generated by the photosensor. The collection of the detection signal results includes information on the internal structure of the sample, as long as the structure represents the spatial distribution and the scattering properties of the scattering centers. The signal processing unit derives an image signal corresponding to an image representing at least a part of the internal structure of the sample from said collection of detection signals.

Another preferred embodiment of the multifrequency spectrometer according to the invention is characterized in that the signal processing system comprises a mixer for deriving the beat signal from the frequency components of the electronic detection signal.

The relative amplitudes of the frequency components of the detection signal represent the frequency dependence of the scatter and / or the absorption properties of scatter centers in the sample. This frequency dependence includes, for example, information on the material composition and the morphological structure of the scattering center described above. The amplitudes of the beat signals of adjacent modulation frequency components are scattered and / or absorbed within the sample at a frequency that is the average modulation frequency above the center frequency of the light from the light source,
It represents the difference between scattering and / or absorption at a frequency that is the average modulation frequency below the aforementioned center frequency. The beat signal has a frequency that is the difference between the frequencies of the respective frequency components of the detection signal. As a result, the beat signal has a frequency that is lower or even lower than the frequency contained in the detection signal itself. Therefore, the beat signal is preferably taken as an input for other signal processing. This is because it does not require a complicated and expensive high frequency signal processing circuit.

Another preferred embodiment of the multi-frequency spectrometer according to the invention is characterized in that the light source is a semiconductor laser.

The choice of semiconductor laser as the light source in a multi-frequency spectrometer has the advantage that it can be frequency-modulated by modulation of the injection current passing through the active layer of the semiconductor laser diode. Modulation of the injected current of the semiconductor laser causes modulation of the refractive index of the active layer of the semiconductor laser. As a result, the output light of the semiconductor laser is frequency-modulated at the modulation frequency of current modulation. Furthermore, because semiconductor laser diodes are so small in size, the choice of semiconductor laser source adds to the design of a compact multi-frequency spectrometer.

Another preferred embodiment of a multi-frequency spectrometer according to the invention comprising an illumination system having an optical modulator for acting on the light generated by a light source to generate light having at least two frequencies is described above. The optical modulator is a frequency modulator.

The use of multi-frequency modulation of the light source is
It has the advantage that the beat signal has substantially no phase noise. Especially for dual multiple frequency transfer modulation spectroscopy,
This is `` Frequency Modulation (FM) Spectroscopy '' G.
Applied Phy-sics B42 (1983) by C. Bjorklund
Year) known from the papers 145 to 152.
Since the beat signals obtained from the two-multiple frequency spectrometer have almost no phase noise, these beat signals are suitable as an input to a signal processing unit for forming an image signal having a high S / N ratio. . Preferably, the frequency band of the light from the light source, that is, the line width of the light source is more than the modulation frequency in order to avoid interference between the modulation frequency of the light source and the frequency within the line width of the center carrier frequency band of the light source. small.

Another preferred embodiment of the multi-frequency spectrometer according to the invention is characterized in that the frequency modulator comprises an optical phase modulator arranged to modulate the phase of the light generated by the light source. The modulator has an optically very high frequency (VHF) phase modulator. In this embodiment, the light source is operated in continuous mode, emitting light in a narrow frequency band, for example in the 1 or a few MHz band. The V
The light from the light source is, for example, 300 GHz ± 10 MH via an HF phase modulator and a low frequency (LF) frequency modulator operating at an RF frequency of, for example, tens or tens of MHz.
It is converted into two-multiplex frequency modulated light with modulation sidebands at the frequency of z.

The VHF optical phase modulator has a stretch of fiber arranged to allow light from the light source to pass through. High frequency optical amplitude modulators, including, for example, dual frequency fiber lasers, pump stretch fibers with amplitude modulated light. Such a high frequency optical amplitude modulator is configured, for example, as a dual frequency fiber laser which forms an amplitude modulation as the beat of two optical frequencies supplied by said dual frequency fiber laser. Dual frequency fiber lasers are
bre grating laser source ”Electro by SVC Hernikov
nics Letters 29 (1993) 1089, 109
Known from page 0 article. The amplitude-modulated pump light causes a modulation of the refractive index of the stretch fiber. Thereby, the light from the light source is phase-modulated at the modulation frequency of the high-frequency light modulator, and the light leaving the fiber of the stretch is frequency-modulated at the modulation frequency of the high-frequency light modulator. A VHF optical phase modulator is formed by coupling a high frequency optical modulator operating at several hundred GHz into the fiber of the stretch.

The LF frequency modulator is preferably electronic.
It is an optical modulator. For example, the alternating voltage supplied to the electro-optical modulator with a frequency of tens or tens of MHz is
The light that passes through the electro-optical modulator produces light that is frequency modulated at the frequency of the alternating voltage. The light from the light source is, for example, 3 by a VHF and LF light modulator.
The light is converted into light that is frequency-division-multiplexed with modulation sidebands at 00 GHz ± 10 MHz.

As another option, the light source is tens or tens of M
Frequency modulated at a relatively low frequency of
The F optical phase modulator performs very high frequency modulation on the low frequency modulated light produced by the light source. As a result of the refractive index modulation by the VHF optical phase modulator, several hundred GHz is obtained.
The dual-multiplex frequency-modulated light having the modulation sidebands in the region of, for example, 300 GHz ± 10 MHz is generated by the second optical phase modulator.

The incorporation of the optical phase modulator to produce modulation sidebands at very high frequencies of a few hundred GHz is preferred in a dual multifrequency spectrometer designed especially for medical imaging. A spectrometer for scattering of human or animal tissue in medical images is employed. Since human or animal tissue contains many liquid parts, the tissue absorption band is a typical liquid absorption band with a frequency band in the range of several hundred GHz to several THz. Efficient detection of these absorption bands is achieved when the modulation frequency of the incident bi-multiple frequency light is as large as the absorption width. If lower frequencies were used, detection would still be possible, but the sensitivity of the spectrometer would then be reduced.

These and other aspects of the invention will be apparent from the embodiments described with reference to the figures.

[0028]

1 shows a diagram of a spectrometer according to the invention. The light source is, for example, the semiconductor laser 1 whose temperature is stabilized by the temperature controller 2. In fact, the temperature controller is formed by a Peltier-effect element, on which the semiconductor laser is mounted. A current is injected by the current source 3 into the semiconductor laser. The semiconductor laser is preferably 750 to 850 so that it can properly penetrate human tissue.
It is a semiconductor laser that emits infrared light having a wavelength in the range of nm. GaAs / AlGaAs semiconductor lasers
For example, it is well suited for this purpose. The wavelength of 780 nm is particularly preferred for studying human or animal tissues, because at 780 nm the absorption of light due to scattering in water and tissues is low. At longer wavelengths, the light exiting the sample will be less intense because the absorption will be stronger due to water, and at shorter wavelengths the scattering in the sample will be much stronger because most of the light will be This is because the sample cannot be removed.

FM modulation of the semiconductor laser output is accomplished by double-multiple frequency modulation of the injection current. For this purpose, the two-multiplex frequency modulator 4 comprises the current source 3
Is combined with The dual frequency modulator 4 is 1G
It is assembled by combining an RF generator 6 operating at Hz and a signal generator 7 operating at 10 MHz with a mixer 5. The high frequency component of the mixer signal is 1 GHz ± 1
The injection current is modulated at these two adjacent RF frequencies because it is selected by a high pass filter 8 which supplies two adjacent RF frequencies of 0 MHz to the current source 3. The light source 1, the temperature controller 2, the current source 3 and the dual frequency modulator 4 form an illumination system. The light beam 32 supplied by the semiconductor laser is the mirror 12
Is focused on the sample 10 by the lens 11 via, so that a small spot of the sample is illuminated.

For example, the sample may be a female breast to be examined for the presence of cancer. The spectrometer according to the invention may also be used to perform image-seeking surgery, which is to image tissue with surgical instruments during a surgical procedure. Light incident on the sample is scattered on and under the surface of the sample. The total amount of light scattered from inside the sample depends on the depth at which the light enters the sample. The depth of penetration depends on the material properties of the sample and the wavelength of the incident light. The mirror 12 is preferably rotatable and the spot 13 of the light beam incident on the sample is scanned over the surface of the sample 10 so that the mirror 12 acts as a sweeping means.

In the spectrometer of FIG. 1, the semiconductor laser 1
An optical sensor 20 sensitive to infrared light in the wavelength range of 10 is set up to block light that is significantly scattered in the backscattering direction. The optical sensor is, for example, a photodiode or a photomultiplier that converts the blocked light into an electronic detection signal. Since the light (generated by the light source 1) is dual-frequency modulated and the scattering in the sample is frequency dependent, the light intensity of the scattered light is the modulation frequency of the dual-frequency modulated light. It changes according to the frequency around. Therefore, the electronic detection signal contains several sidebands with different amplitudes in the Fourier transform. The beat signal from the electronic detection signal is formed to represent a difference in amplitude of the sidebands of the electronic detection signal. For this purpose, the electronic detection signal may be amplified by a preamplifier 27 to emphasize this signal amplitude before other processing steps are carried out, some of which may be lost. A low frequency component having a frequency up to several MHz of the electron detection signal is held by applying the electron detection signal to the low pass filter 21. The low frequency component is associated with a slow temporal change at a frequency equal to the difference between the two frequencies of the two multi-frequency modulated incident light.
Since the low-pass filter has a cut-off frequency at 1 or a few times 10 MHz, for example at 30 MHz, only the component of the electronic detection signal having a frequency equal to the difference in the frequencies of the modulation sidebands. Filter 2
Pass 1. Thus, the component of the electronic detection signal having the frequency of the modulation sideband at 1 GHz ± 10 MHz is
It is removed by the low pass filter 21. The low frequency component from the low pass filter 21 is amplified by the amplifier 22. The 10 MHz signal of the signal generator 7 is 20M
The frequency is doubled by the frequency doubler 23 which supplies the Hz vibration signal. The amplified low frequency component of the electronic detection signal and the vibration signal are mixed by a signal mixer 24 that beats the amplified low frequency component with respect to the vibration signal. Therefore, the signal mixer 24 has an amplitude that depends on the difference between the scattering properties of the sample 10 with respect to the frequency components of the two-multiplex frequency modulated incident light beam, and has a low frequency with a frequency band of the RF frequency around 20 MHz. Form the beat signal. The low frequency beat signal is, for example, the amplifier 22 and the preamplifier 2
There may be spread frequencies due to electronic noise created by 7. To remove this noise, the low frequency beat signal is fed to a low pass filter 28 having a cutoff frequency of only a few kHz. The low pass filter 28 forms a monitor signal representing the DC component of the low frequency beat signal.

The photo-detecting device 25 includes a photo-sensor 20, and further has a combination of the low-pass filter 21, the amplifier 22, the frequency doubler 23 and the signal mixer 24. The light detection device 25 detects the light scattered in the sample 10 and supplies the monitor signal to the signal processing unit 26. A signal processing system arranged to process the electronic detection signal from the optical sensor comprises the preamplifier 27, the lowpass filter 21, the amplifier 22, the mixer 24 with the frequency doubler 23 and a lowpass filter 28. .

The portion of the scattered light emitted from the sample 10 which is captured by the photosensor with a narrow range of scattering angles is selected by the aperture 30. The aperture 30 has a circular slit hole that allows light from the sample 10 to pass in propagation directions having a narrow range of angles around θ from the center ray of the incident light beam. Since the light of the narrow beam 32 illuminates the sample 10, the light passing through the aperture 30 corresponds to a narrow range of scattering angles. Further, the aperture 30 is preferably circular to allow light to pass through regardless of the deflection angle φ. Therefore, the intensity of light collected by the photosensor 20 is integrated over a range of 2π with respect to the deflection angle φ to collect maximum brightness intensity. The light that has passed through the opening 30 is collected by a lens 33 that focuses the light to the photosensor 20. That is,
Lenses 11 and 33 form an optical system that images the output surface of the illumination system onto the photosensor through the sample. The aperture 30 is preferably variable to change the narrow range of scattering angles of the light collected by the photosensor 20. In particular this is achieved by mechanically adjusting the circular hole 31.

FIG. 2 shows a diagram of another embodiment of the spectrometer according to the invention. The semiconductor laser 1 is driven by a DC current source 3 that drives the semiconductor laser in the CW mode. The light exiting the semiconductor laser 1 is coupled into an optical fiber 40. A very high optical frequency (VHF) modulator 41 and a low optical frequency modulator 42 are each coupled to the optical fiber 40. The VHF optical modulator 41 is preferably a very high frequency (VHF) phase modulator 41, which may be several hundred G
Since the phase modulation of the laser light is performed at a very high modulation frequency of Hz, eg 300 GHz, the VHF light modulator 41 produces high frequency FM modulated light with frequency modulation at a modulation frequency of a few hundred GHz. Low frequency (L
The frequency modulator 42 of F) performs low frequency modulation to the high frequency modulated light at an RF frequency of tens or tens of MHz, for example, 10 MHz. Therefore, the LF frequency modulator 42 supplies the two-multiplex frequency modulated light having a modulation frequency of, for example, 300 GHz ± 10 MHz. The two multi-frequency modulated light is incident on the sample space as described above with reference to FIG. 1, and the light scattered in the sample space is also described above with reference to FIG. Detected.

The VHF optical phase modulator 41 has several hundred GH.
It has a high frequency optical amplitude modulator 43 which supplies light which is amplitude modulated at the modulation frequency of z. Such high frequency optical amplitude modulators are configured, for example, as dual frequency fiber lasers which form the amplitude modulation as two optical frequency beats supplied by a frequency doubled fiber laser. For more information on dual frequency fiber lasers, see Dual frequency all fiber grating laser source.
e ”SVC Hernikov Electronics Letters 29 (199
3), pages 1089 and 1090.

The amplitude-modulated light is coupled into the fiber 40 by the optical coupler 44. The amplitude modulated light produces a refractive index of the fiber 40 which varies with the modulation frequency provided by the high frequency light modulator 43. The refractive index change is a result of non-linear electro-optic coupling. In other words, the index of refraction of the fiber material depends on the amplitude of the electric field in cooperation with the amplitude modulated light coupled into the fiber. Due to the varying refractive index, the phase of the incident light from the semiconductor laser is modulated at the modulation frequency of the high frequency light modulator. Therefore, the optical coupler 44 functions as an optical phase modulator. As a result, the light of the VHF optical phase modulator 41 is, for example, 300 from the center optical frequency of the light.
Provides high frequency modulated light with modulation sidebands at GHz.

The high frequency modulated light is then fed through a mirror 12 to an LF frequency modulator 42 which produces a double multiplexed frequency modulated output light which is focused on the sample 10 by a lens 11. . The LF frequency modulator 42 has an electro-optical modulator 45 including an electro-optical liquid crystal 46 that supplies an alternating voltage at a frequency of tens or tens of MHz, for example 10 MHz. The AC voltage is AC source 4
7 produces a modulation of the refractive index of the electro-optical liquid crystal 46 at the frequency of the alternating voltage. Due to the refractive index modulation of the electro-optical liquid crystal 46, the high frequency modulated light from the VHF light modulator is tens or tens of MHz.
Is modulated again with the frequency of
The high frequency modulated light supplied by the HF optical phase modulator 41 is converted into double multiplexed frequency modulated light having a modulation sideband of 300 GHz ± 10 MHz, for example.
Preferably, the line width of the semiconductor laser is lower than the modulation frequency of the two-multiple frequency modulated light. When the two multiplex frequency modulation frequencies are close together, a high frequency signal processing circuit of, for example, 20 MHz which is neither complicated nor expensive is required. However, because optical sensors and signal processing circuits for processing signals at approximately 100 MHz are commonly used today, modulation sidebands may be separated by up to 100 MHz.

An optical filter 48 is placed in front of the lens 11 to prevent the amplitude-modulated light from the high frequency optical amplitude modulator 43 from reaching the sample 10. Preferably, the amplitude-modulated light from the high-frequency amplitude modulator 43 has a wavelength that is appreciably different from the wavelength of the two-multiplex frequency-modulated light, and the transfer characteristics of the optical filter 48 are two or more. Blocking the light from the light source 1 that is double frequency modulated, but blocking the light produced by the high frequency optical amplitude modulator and causing the index modulation in the optical coupler 44. It is provided to allow. As another choice,
In the optical filter 48, the wavelength of the two-multiplexed frequency modulated light is in the propagation range of the dichroic mirror, while the wavelength of the light modulated in amplitude from the high frequency optical amplitude modulator 43 is the reflection range of the dichroic mirror. It may be formed by a dichroic mirror arranged as in, so that the amplitude modulated light does not reach the sample 10.

FIG. 3 is a view showing still another embodiment of the spectrometer according to the present invention. The light beam 32a from the light source 1 is formed into a parallel beam 32b by the collimator lens 15. The light from the light source 1 is then focused by the lens 11 onto a small portion 14 of the sample illuminated by the convergent beam 32c. The aforementioned small portion is located at the optical path length from the lens 11 equal to the focal length of the lens 11. The small portion of the sample where the light of the convergent beam 32c is focused is selected by choosing the position of the lens 11 movable along the two arrows 16. The scattered light leaving the sample from the small sample portion 14 and passing through the circular slit hole 31 is collected by the collecting lens 33.
To form a parallel beam 34. Since the lens 11 is positioned to collect the incident light on the small sample portion, the area around the small sample portion 14 is eventually only weakly illuminated. Behind said collecting lens 33, a focusing lens 35 is provided with an incident parallel beam 34
Is positioned so as to focus on the pinhole diaphragm 36. Only light leaving the small sample portion 14 may pass through the pinhole stop 36, originating from outside the small sample portion 14 and nevertheless passing through the focusing lens 35, the parallel beam 34. It will be focused outside the pinhole with a different propagation direction than and blocked by the pinhole diaphragm 36. Light passing through the pinhole diaphragm 36 originates only from the small sample portion 14 and contains scattering information for that portion only and is collected by another lens 37 to be focused on the light sensitive surface of the photosensor 20. Because only the small sample portion 14 is the lens 33.
, Which is sharply imaged on the pinhole diaphragm 36, which receives little light from the area around the small sample portion 14 and is at the focal point.
The lenses 11 and 33 are incorporated into the optical system and at their common focus the small sample portion 14
Form a confocal arrangement with. In the embodiment according to FIG. 3, the optical system for imaging the output surface of the illumination system through the sample 10 onto the photosensor 20 comprises the lenses 11, 33 or lenses 15, 36,
37 and the pinhole diaphragm 36. By adjusting the position of lenses 11 and 33 with respect to the sample, the position of the small sample portion is varied, from which scattered light is collected at the photosensor. As a result, the position-variable lenses 11 and 33 together with the rotating mirror 12 are arranged to sweep the light beam over the sample and thus included in the sweeping means. The lens 33 is therefore positionally variable, as indicated by the two arrows 38, so that the small sample portion 14
Is at a distance from the lens 33 equal to the focal length of the lens 33. Crosstalk from the area around the small sample portion is further reduced by the pinhole diaphragm 36 acting as a spatial filter.

Instead of bi-multiplex frequency modulated light as described above, a spectrometer may use three or more frequency-multiplexed modulated lights and may be employed to interrogate the sample. The relative amplitude of the frequency components of the detected signal represents the frequency dependence of the scattering and / or absorption properties of scattering centers within the sample. More multiplexed modulation frequencies can be used, and more spatial information of scattered light can be extracted from the detection signal.

[Brief description of drawings]

FIG. 1 shows a spectrometer according to the invention.

FIG. 2 is a diagram showing another embodiment of the spectrometer according to the present invention.

FIG. 3 is a diagram showing still another embodiment of the spectrometer according to the present invention.

[Explanation of symbols]

1: semiconductor laser, 2: temperature controller,
3: DC current source, 4: dual frequency modulator, 5: mixer, 6: RF generator, 7: signal generator,
8: High-pass filter, 10: Sample,
11: lens, 12: mirror,
13: spot, 15: collimator lens, 20: optical sensor, 21: low-pass filter, 22: amplifier, 23: frequency doubler, 24: mixer, 25: photodetector, 26: signal processing unit, 27: preamplifier, 28 : Low-pass filter, 3
0: aperture, 31: circular hole, 32: light beam, 33: collecting lens, 34: parallel beam, 35: focus lens, 36: diaphragm,
37: other lens, 40: optical fiber, 4
1: VHF optical modulator, 42: low frequency modulator, 4
3: high frequency optical amplitude modulator, 44: optical coupler, 4
5: Electro-optical modulator, 46: Electro-optical liquid crystal, 47:
AC source, 48: Optical filter

Claims (8)

[Claims] 1. A light source (1) for illuminating at least part of a sample space with light having at least two frequencies.
With an illumination system (1, 2, 3, 4), a frequency sensitive photodetector (25) with an optical sensor (20) for detecting light leaving the sample space, via a sample in the sample space An optical system (11, 33) for imaging the output surface of the illumination system onto the photosensor and a signal processing system (27, 28, 22) for processing electronic detection signals from the photosensor (20). , 23, 2
4) A multi-frequency spectrometer having 4), wherein the photosensor is positioned to receive the light scattered by the sample (10). 2. A multi-frequency spectrometer according to claim 1, wherein the illumination system (1,
In a multi-frequency spectrometer in which 2, 3, 4) are arranged to illuminate a portion (13, 14) of the sample space with a narrow light beam (32), the optical sensor (20) comprises the illumination system (20). Positioned to receive light scattered by the sample (10) along a direction different from the direction in which the narrow light beam (32) from (1, 2, 3, 4) is incident on the sample. Characteristic multi-frequency spectrometer. 3. The multifrequency spectrometer according to claim 1 or 2, wherein the optical system (33, 35, 36, 3).
7) A multi-frequency spectrometer characterized in that it comprises a confocal optical arrangement. 4. The multifrequency spectrometer according to claim 1, wherein the optical system (33,
35, 36, 37) is the illumination system (1, 2, 3, 4) over at least a portion of the sample (10).
A multi-frequency spectrometer, characterized in that it comprises sweeping means (12, 16, 38) for sweeping the light beam (32) from. 5. The multi-frequency spectrometer according to claim 1, wherein the signal processing system (2)
7, 21, 22, 23, 24, 28) has a mixer (24) for extracting a beat signal from the frequency component of the electronic detection signal. 6. A multifrequency spectrometer according to any one of claims 1 to 5, characterized in that the light source (1) is a semiconductor laser. 7. The multi-frequency spectrometer according to claim 1, wherein the illumination system (1, 2,
A multi-frequency spectrometer, 3, 4) having a light modulator (41) for acting on the light generated by said light source to generate light with said at least two frequencies, wherein said light modulator is frequency modulated A multi-frequency spectrometer characterized by being a vessel. 8. A multi-frequency spectrometer according to claim 7, wherein the frequency modulator (41) comprises an optical phase modulator (44) arranged to modulate the phase of the light generated by the light source. A multi-frequency spectrometer characterized by having.