JP3770976B2 - Photodetector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a non-detection apparatus having a high detection efficiency and a high multiplication factor, which is important in measurement of a non-classical light source or other measurement requiring a high signal / noise ratio.
[0002]
[Prior art]
Conventional photodetection devices can be roughly classified into the following three types.
[0003]
(1) A semiconductor is used as a detection surface, and light absorbed by the semiconductor forms a pair of electrons and holes, and these are composed of an internal photoelectric effect that becomes a carrier of current.
[0004]
(2) A so-called photocathode produced by growing various alkali metals or the like generates an electric current effective for detection by extracting electrons from the surface, and is called an external photoelectric effect.
[0005]
(3) There are three types of pyrometers that perform optical measurement using the fact that the temperature of the thin film rises by absorbing light into the thin film.
[0006]
Not only can all conventional photomultiplier tubes be used among conventional photodetection devices, but also non-classical light (squeezed light, number states, Detection of light in the sub-Poisson state can be measured without destroying the signal / noise ratio of the state, so weak signals that were previously buried in noise and could not be measured Can be measured.
[0007]
A characteristic example of these is the detection of gravity waves. This is because when a gravitational wave generated in the process of a very large mass change due to the generation of a black hole or a supernova explosion is detected using light, the modulation of the light field by the gravitational wave is very small. Therefore, it was impossible to detect this with conventional light (laser light or the like). However, if measurement is performed using light in a very high squeezed state, information on the phase delay of the light to be detected can be detected with high accuracy. Holes and supernova explosions and double star measurements are possible.
[0008]
[Problems to be solved by the invention]
In the present invention, the above (1) and (2) are applicable ranges in consideration of the accuracy and the response speed of detection.
[0009]
Although high detection accuracy, efficiency, noise characteristics, and amplification gain are important elements as a photodetector, the semiconductor detection element and the photocathode are good and bad in the conventional techniques (1) and (2) described above. That is, the semiconductor detection element has a relatively high quantum efficiency, but uses many electronic components in the multiplication process when making a signal until it can be observed, and all these individual elements cause noise. Thus, amplification fluctuation and thermal noise are introduced into the system.
[0010]
On the other hand, in the process of converting incident light into electrons, the photocathode has a photocathode thickness of several thousand mm, so that many photoelectrons fall into the internal electron trap, Because of the low probability of getting out of the vacuum potential, a quantum efficiency of only about 30% has been achieved at most. However, once converted into electrons and taken out in a vacuum, energy is sent to the electrons by applying an external voltage, and the secondary electrons generated when this collides with a metal surface, etc. In order to allocate that energy, an efficient multiplication is achieved here. Furthermore, by continuously performing this in multiple stages, it is possible to achieve a higher signal / noise ratio.
[0011]
However, there is currently no photodetector that combines the good points of both.
[0012]
SUMMARY OF THE INVENTION An object of the present invention is to provide a photodetection device that combines the above-mentioned advantages, that is, has a relatively high quantum efficiency and can achieve efficient multiplication.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides
[1] In the light detection device, the incident light between the transparent and homogeneous right-angle prism and the side where the incident light of the right-angle prism is incident and the side where the emitted light is emitted are incident on the incident light. A low-refractive-index dielectric film having a refractive index lower than the refractive index of the right-angle prism uniformly deposited or grown on a side that totally reflects incident light, and a metal or semiconductor thin film on the low-refractive-index dielectric film includes a light detection unit which have the said total reflection surface near the optical field in the vicinity of the occurs, is scattered by the metal or semiconductor thin film, light absorbed in the thin film surface of the metal or semiconductor, the metal Alternatively, it is converted into electrons within a semiconductor thin film surface and taken out as an electric signal .
[0014]
[2] The optical detection device described in [1] Symbol mounting comprises means for controlling the polarization state spatial shape of the incident light with.
[0015]
[ 3 ] The photodetector according to [ 2 ], further including a control unit that controls a polarization state depending on an incident wavelength.
[0016]
[ 4 ] In the photodetecting device according to [ 3 ], an electric field that draws electrons in a thin film of metal or semiconductor induced by incident light and guides the electrons to an electron multiplying mechanism or an electron deflecting mechanism installed behind the thin film. Means for applying.
[0017]
[ 5 ] In the light detection device according to [ 4 ] above, after rotating the polarization plane of the component which is reflected between the window material and the low refractive index dielectric film surface and is not photoelectron-converted, the conversion is performed again. Means for making incident on the surface;
[0018]
[ 6 ] In the light detection device according to any one of [1] to [ 5 ], the incident light is decomposed into orthogonal components through an optical demultiplexer by polarization, and then converted into each polarization. On the other hand, the detection devices were arranged one by one, and after detection, the signals were electrically coupled again.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0020]
FIG. 1 is a configuration diagram of a high-efficiency photodetection device showing the basic structure of the present invention.
[0021]
As shown in this figure, incident light 1 is incident on a right angle prism 2 at an angle, so that a right angle prism 2 as a window material and a dielectric (low refractive index) having a refractive index lower than the refractive index of the prism 2 are obtained. 100% reflection can be caused between the dielectric film 3. This state is called total reflection. Here, for example, the dimension L of the incident side and the outgoing side of the right-angle prism 2 is 10 mm.
[0022]
The condition of total reflection at this time is sin θ = n ₂ / n ₁ when the incident angle with respect to the normal of the surface is θ as shown in FIG. Here, n ₁ and n ₂ are the refractive indexes of the right-angle prism 2 and the dielectric film 3. In the case of incidence at this angle θ or more, the condition of total reflection is satisfied. In the vicinity of the reflecting surface, a near light field 4 as schematically shown in FIG. 2 is generated, and this reaching region is about the wavelength of the incident light 1. When a metal (gold, aluminum) or semiconductor thin film 5 is inserted into this region, part or all of the reflected light is scattered or absorbed inside the film to generate electron-hole pairs or electron-ion pairs. Such a state is called attenuated total reflection (Attenuated Total Reflection). Under this condition, only the component of the incident light whose polarization direction is parallel to the normal of the opposite surface (so-called TM component) is scattered by the metal or semiconductor thin film 5 through the near light field 4. The remaining TE component perpendicular to the normal is reflected by the right-angle prism 2 and the dielectric film 3 surface.
[0023]
On the other hand, the light absorbed on the surface of the metal or semiconductor thin film 5 is converted into electrons in the surface of the metal or semiconductor thin film 5, but if the film thickness is sufficiently thin, the electrons are in a high energy state and easy Since it is equivalent to the potential wall between the vacuum and the tunnel effect and is emitted into the vacuum, most of the electrons caused by the incident light 1 can be driven out into the vacuum. Furthermore, after accelerating the electrons taken out to the vacuum field, various electron optical techniques can be achieved by passing through the secondary photomultiplier mechanism and the photoelectron deflection mechanism 6. Furthermore, the result can be captured by a metal plate and taken out as an electrical signal.
[0024]
The low refractive index dielectric film used here is optically transparent such as MgF ₂ and has a refractive index of 1.3 compared to optical glass (refractive index of about 1.5) which is a prism material. Considering that the reach distance of the near light field is at most about a wavelength, it is considered that the thickness is about 500 mm. However, it is experimentally possible to optimize the thickness.
[0025]
On the other hand, the metal or semiconductor thin film 5 deposited on the dielectric film 3 may be a metal thin film such as gold or aluminum, or a semiconductor thin film such as silicon or gallium arsenide. In this case, the thickness in the case of a metal thin film is estimated to be about 50 to 200 mm, but this is also considered to be a parameter that is basically optimized experimentally. Further, a thin film such as silicon as a semiconductor can be uniformly formed by using various crystal growth methods, but the thickness is considered to be the same as that of a metal.
[0026]
As an example of the window material, FIG. 1 shows an example in which the right-angle prism 2 is used. However, a near light field 4 generated between the dielectric films 3 and a metal optically coupled via the near light field 4 or Since a structure such as a semiconductor surface is important, if the bottom of the glass is sufficiently flat, it is not particularly necessary to have a prism structure, and it may be a lens shape or a wedge shape.
[0027]
Next, as described above, the component bonded to the metal or semiconductor thin film 5 by the near-field 4 is a TM component. In ordinary light sources and light-emitting phenomena, the polarization is often random. Therefore, controlling the polarization plane in advance before entering the detection surface provides an efficient measurement method.
[0028]
FIG. 3 is a configuration diagram of a high-efficiency photodetection device showing a first embodiment of the present invention.
[0029]
First, in order to control the spatial shape of incident light and its polarization characteristics, the light from the light source 11 is once collimated by a collimator lens 12 or the like, and passed through an aperture 13 or the like as a spatial filter. As a result, only the above-described spatial component in which the incident light is totally reflected is guided to the light detection structure shown in FIG. Furthermore, among them, only one polarization component (for example, TM component) among the polarization components is selected by the polarizing plate 14 and guided to the light detection unit 19, but from the delicate polarization due to the arrangement of the light detection unit 19 at that time. In order to correct the deviation, it is necessary to use the wave plate 15 or the like. In FIG. 3, 16 is a right-angle prism, 17 is a dielectric film, and 18 is a metal or semiconductor thin film.
[0030]
FIG. 4 is a configuration diagram of a high-efficiency photodetection device showing a second embodiment of the present invention.
[0031]
In this embodiment, as shown in FIG. 4, in order to detect the light from the light source 21 as effectively as possible, the polarized light is applied by the wave plate 24 so that the detection efficiency of the incident light from the light source 21 is the highest. Further, the TE component light that has not been detected by total reflection is reflected by the reflecting mirror 29 toward the light detection unit 30 again.
[0032]
At this time, the polarization component is subtly corrected using the wave plate 28 so that the reflected light again matches the TM component of the light detection unit 30. Thereby, the light from the light source 21 that has passed through the aperture 23 can be efficiently detected. In FIG. 4, 22 is a collimator lens, 25 is a right-angle prism, 26 is a low refractive index dielectric film, and 27 is a metal or semiconductor thin film.
[0033]
FIG. 5 is a configuration diagram of a high-efficiency photodetection device showing a third embodiment of the present invention.
[0034]
As shown in this figure, in this embodiment, after the light from the light source 31 is spatially controlled, it is divided into orthogonal polarization components by the polarization beam splitter 34, and the independent light detection unit detects each component. 38 and 44 are provided.
[0035]
The detected electric signals of the respective polarization components are combined via an electric mixer 45 and finally led to an analysis device. At this time, not only a high detection efficiency equivalent to that of the second embodiment is obtained, but also a time delay occurs because the polarized component extracted to the outside is reflected once and guided to the light detection unit. May give restrictions.
[0036]
Accordingly, since it is easy to eliminate these optical or electrical delay time differences by using two photodetecting units 38 and 44 as shown in FIG. 5, a highly efficient photodetection device excellent in time response. Can be provided. In FIG. 5, 32 is a collimator lens, 33 is an aperture, 35 is a first right-angle prism, 36 and 42 are low-refractive-index dielectric films, 37 and 43 are thin films of metal or semiconductor, and 41 is a second right-angle prism. is there.
[0037]
In addition, this invention is not limited to the said Example, A various deformation | transformation is possible based on the meaning of this invention, and these are not excluded from the scope of the present invention.
[0038]
【The invention's effect】
As described above in detail, according to the present invention, it is possible to provide a high-efficiency photodetector that has a relatively high quantum efficiency and that can achieve efficient multiplication. In particular, high detection efficiency and high multiplication factor, which are important in measurement requiring a high signal / noise ratio, can be achieved.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a high-efficiency photodetection device showing a basic structure of the present invention.
2 is a schematic diagram of a light detection unit of the high-efficiency light detection device in FIG. 1;
FIG. 3 is a configuration diagram of a high-efficiency photodetection device showing a first embodiment of the present invention.
FIG. 4 is a configuration diagram of a high-efficiency photodetection device showing a second embodiment of the present invention.
FIG. 5 is a configuration diagram of a high-efficiency photodetection device showing a third embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Incident light 2,16,25,35,41 Right angle prism 3,17,26,36,42 Dielectric (low refractive index dielectric) film | membrane 4 Near optical field 5,18,27,37,43 Metal (gold, 6) Photomultiplier mechanism or photoelectron deflector mechanism 11, 21, 31 Light source 12, 22, 32 Lens 13, 23, 33 Aperture 14 Polarizing plate 15, 24, 28 Wave plate 19, 30, 38, 44 Photodetector 29 Reflector 34 Polarizing beam splitter 45 Electric mixer

Claims (6)

With respect to the incident light, a transparent and homogeneous right-angle prism, and the incident light between the side where the incident light of the right-angle prism is incident and the side where the emitted light is emitted are incident, and the incident light is totally reflected. comprising a low-refractive-index dielectric film having a lower refractive index than homogeneously deposited or grown refractive index of the right-angle prism, the light detection unit which have a thin film of a metal or semiconductor to the low refractive index dielectric film In the vicinity of the total reflection surface, a near light field is generated, scattered by the metal or semiconductor thin film, and absorbed by the metal or semiconductor thin film surface. Photodetector characterized in that it is converted into an electric signal and extracted as an electrical signal . The optical detection apparatus of claim 1 Symbol placement, optical detection device including means for controlling the polarization state spatial shape of the incident light with. 3. The photodetector according to claim 2, further comprising a control unit that controls a polarization state depending on an incident wavelength. 4. The light detection device according to claim 3, wherein means for applying an electric field for extracting electrons in a thin film of metal or semiconductor induced by incident light and guiding them to an electron multiplication mechanism or an electron deflection mechanism installed behind the thin film is provided. Photodetector with 5. The photodetector according to claim 4 , wherein a polarization plane of a component which is reflected between the window material and the low refractive index dielectric film surface and is not photoelectron-converted is rotated and then incident on the conversion surface again. Photodetector having means. The optical detection device according to any one of claims 1 to 5, with respect to the incident light, through an optical demultiplexer according to polarization, after decomposing each quadrature component for each of the polarization, the detector Photodetectors that are arranged one by one, detected, and then electrically coupled again.

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