JPH0432728A - Method and device for coherent light selective spectral diffraction - Google Patents

Abstract

PURPOSE:To increase the quantity of incident light for spectral diffraction and to increase energy per unit area by extracting the 0th-order component of a Fraunhofer diffracted image through a pinhole with a specific aperture diameter or a slit. CONSTITUTION:A pinhole plate P which has the aperture diameter D is arranged at the focus position of a lens L0 and when a plane wave S0 is made incident from the side of the pinhole P, the light which passes through the aperture of the pinhole P is propagated like a wave Q2 including a spherical wave component and converted into a plane wave S2 by a lens L1. For the purpose, the pinhole P which is smaller than the size of the 1st dark ring of the Fraunhofer diffracted image which is determined by the aperture diameter and focal length of the lens L1 and the wavelength is arranged and a lens L2 which matches the size of the pinhole of the 1st dark ring of the Fraunhofer diffracted image determined by the lens L0 and is larger in diameter than the lens L1 is used to increase the energy density by the area ratio of the lenses L1 and L2 without any loss of the plane wave component S1 in luminous flux emitted from a light emission plane.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a coherent light selective spectroscopy device.

[Conventional technology]

Traditionally, it has been used as a basic component of spectrophotometers that measure the absorption spectrum of light and fluorescence spectra that are used as a means of analyzing substances, and it can also be used to measure emission spectra, etc. The spectrometers used are widely known.

Such a conventional spectrometer will be explained with reference to FIGS. 11 and 12.

In Fig. 11, light from a light emitter L is extracted by a slit 2 so that it can be regarded as a linear light source, and the light from the linear light source is converted into a bundle of parallel lights by a lens system L1 whose front focus is at the position of the slit 2. and a slit 4 placed at the back focal position of the lens system Ll, and a lens L whose focal plane is the slit 4.
2, the linear component of the light emitted from each point light source of the slit (
Only a bundle of light beams (plane waves) is extracted and made incident on the diffraction grating 5. When the interference light generated by the diffraction grating 5 is imaged and detected by the lens L3 on the detector 7, each wavelength component included in the plane wave is angularly dispersed on the output side of the diffraction grating, allowing spectroscopic measurement.

In FIG. 12, a Cassegrain optical system is used to collect light from a slit 2, which can be regarded as a linear light source, to increase the amount of light, and the other configurations are the same as in FIG. 11.

Here, FIGS. 11 and 12 show examples of transmission type diffraction gratings, or in the case of reflection type diffraction gratings, the diffraction grating 5 is of the reflection type, and the lens L3 and the detector 7 are placed on the lens L2 side. and perform spectrophotometry. Also, lesbian Ll, L2. L3 also uses a reflector.

[Problem to be solved by the invention] By the way, in the conventional spectrometer, the light from the light emitter 1 is extracted with a slit, and the light transmitted through the slit is made into a state where it can be regarded as a line light source made up of a collection of point light sources. Ta. This is based on the idea that if the light source has a large size, different wavelength components emitted from different positions of the light source may be detected by a spectrometer as the same wavelength component, and accurate wavelength dispersion cannot be achieved. It is something. Therefore, conventionally, when determining the ideal resolution, as shown in Fig. 11, the slit 2 with an infinitesimal aperture is used as a point light source or lined up in a line, and the lens system L1, the sleeves 1 to 4, and the lens L2 are used. Only a bundle of light beams with a straight component (a plane wave traveling in the optical axis direction) was obtained. However, in this conventional method, the light source is treated as having an infinitesimal width, so the amount of light is extremely small. Therefore, it is necessary to increase the amount of light by increasing the slit width at the expense of resolution, or to keep the slit width constant. In this case, the problem was how to increase the solid angle of incidence. Therefore, in FIG. 11, a large-diameter lens is used to increase the light receiving angle, and in FIG. 12, a Cassegrain light receiving system is used to increase the solid angle of incidence to increase the amount of light. Such a conventional method of increasing the amount of light by increasing the solid angle of incidence is suitable when the light emitting body to be dispersed can be regarded as a point light source, or when it is a linear light source that is almost the same as the entrance slit.

However, if the light emitter is large, such as a surface emitting light, only the part that is the same as the entrance slit is used for spectroscopy, and the rest is discarded.

The present invention was made in view of these points, and is suitable for surface emission where the emission spectrum can be considered to be almost the same over the entire area, dramatically increasing the amount of incident light for spectroscopy, and reducing the energy per unit area. The purpose of the present invention is to provide a coherent light selective spectrometer capable of increasing the density of light.

[Means to solve the problem]

The present invention forms a Fraunhofer diffraction image by passing light from a sample through an optical system, and converts part or all of the zero-order component of the Fraunhofer diffraction image, or a part of a slit-like component with the same width as the zero-order component. Alternatively, it is characterized by extracting all of it and performing spectroscopic measurements.

[Operation] The present invention takes advantage of the fact that by extracting the zero-order component of a Fraunhofer diffraction image of light from a sample such as a surface emitter, a rectilinear component parallel to the optical axis can be obtained. The O-order component of the diffraction image, or 0
Part or all of the slit-like component with the same width as the next component is extracted using a pinhole or slit with a predetermined aperture diameter, and unlike conventional methods, the target is not a point or line light source. Therefore, it is possible to dramatically increase the amount of light (2) and perform spectroscopy. By condensing the light from the surface light emitter with a large-diameter lens and converting it into a small-diameter luminous flux, it becomes possible to further increase the energy per unit area and perform spectroscopy.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings.

First, the spectroscopic method of the present invention will be explained with reference to FIGS. 1 to 3.

As shown in FIG. 2, when coherent light is incident on the lens LO, a Fraunhofer diffraction image is observed at the position of the focal length f. This is called an Airy disk, and if a circular lens is used, a circular dark ring will be formed, and the area within the first dark ring with a diameter corresponding to the lens aperture, that is, the 0th order component, will be the brightest area. , a wavefront equivalent to that of a plane wave incident on an aperture having the size of this first dark ring is formed. Now, the aperture diameter of the circular lens is D
Dr is given by r, focal length is f, diameter of the first dark ring is D, and wavelength is λ.

This can be done by placing a pinhole plate P with an aperture diameter at the focal position of the lens LO, as shown in FIG. 3(A), and
If coherent light in the optical axis direction of O is incident, a divergent spherical wave Q2 is emitted from the aperture diameter of the pinhole plate P,
It becomes a plane wave S2 at the lens Ll. This can be seen in Figure 3 (
When a plane wave SO enters from the pinhole P side as shown in B), the light passing through the pinhole aperture propagates as a wave Q2 containing a spherical wave component due to diffraction, and is converted into a plane wave S2 by the lens I71. It means to be done.

Therefore, by arranging a pinhole smaller than the size of the first dark ring of the Fraunhofer diffraction image of equation (1) determined by the aperture diameter, focal length, and wavelength of the lens L1, the first dark ring of the Fraunhofer diffraction image determined by the lens LO is By using a lens that matches the size of the ring pinhole 9 and has a larger aperture than the lens L1, the plane wave component Sl in the light beam emitted from the light emitting surface is not lost, and the distance between the lenses L1 and L2 is reduced. A higher energy density can be extracted by increasing the area ratio. Furthermore, by arranging a slit with the same width as the pinhole size in the direction of the diffraction grating groove instead of a pinhole, the energy in the slit height direction can be generated as before, dramatically increasing the amount of incident light. It is possible to perform spectroscopic measurements.

FIG. 1 is a diagram for explaining the coherent light selective spectroscopy method of the present invention based on this idea. In the figure, S
is a surface light emitter, LO is a lens, P is a pin pole plate, Ll,
L2 is a lens, G is a transmission type diffraction grating, and D is a detector.

The lens LO is a convex lens with a large light-receiving aperture, and a surface light emitter S of a sample to be subjected to spectroscopic measurement, such as a biological sample, is placed at an arbitrary position in front of the lens. The sleeve L-plate P is the lens LO
It is placed almost at the focal point of the
), and has a size (diffraction limit) that allows only the 0th order component (straight component) of the light beam arranged in a slit shape of the Fraunhofer diffraction image by the lens LO to be transmitted.

Note that the slit width may be large enough to allow a portion of the 0th-order diffraction image to pass through. The L lens L1 is a small diameter lens whose focal plane is the pinhole position, and the lens ■
, 0 and the F value are the same, the purpose is to extract all the zero-order components formed at the pinhole position by the lens LO to obtain a plane wave.

A transmission type diffraction grating G is arranged behind the lens Ll, and the diffracted light is imaged onto the detector by the lens L2.

In such a configuration, light from the surface light emitter S is received]
When the light is focused by a lens LO with a large diameter and a Fraunhofer diffraction image is formed at the pinhole position, the binpole diameter is (
Since it satisfies Equation 1j, only the 0th-order diffraction image of the Fraunhofer diffraction image is transmitted, is converted into a parallel beam by the lens Ll, and enters the transmission type diffraction grating G. Since the emission angle of the diffraction grating G differs depending on the wavelength, spectroscopic measurement can be performed by focusing this diffracted light onto the detector using the lens L2.

2, in the present invention, the straight component from the surface light source is focused by the lens LO with a large light receiving aperture, and the pinhole diameter is expanded to the diffraction limit to extract the straight component, unlike the conventional method. Compared to the case where the light flux from a point light source or a line light source is detected at a wide angle, it is possible to significantly increase the amount of light. Note that by making the aperture of the lens LO larger than the aperture of Ll and keeping the F value the same, the energy per unit area of the linear component incident on the diffraction grating G can be increased by the area ratio of both lenses. I can do it.

FIG. 4 is a diagram showing another embodiment of the present invention using a Cassegrain optical system.

In this embodiment, light from a surface light emitter (not shown) is taken into the Cassegrain optical system 10 through the aperture 11, a Fraunhofer diffraction image is formed at the position of the pinhole plate P by the convex mirror 13 and the concave mirror 12, and the straight component is formed by the pinhole. The beam diameter is further reduced using a concave mirror 16 and a convex mirror 17, and the beam is extracted as a plane wave through the aperture 15, and is made to enter a diffraction grating (not shown).

In this embodiment as well, the luminous flux taken in by the aperture 11 is
By converting to a diameter of 5, the energy density can be increased.

FIG. 5 is a diagram showing another embodiment using a camera lens.

In this embodiment, a camera lens 20 with a large diameter and a small F value captures light from a surface light emitter (not shown), the 0th order diffracted light of the Fraunhofer diffraction image produced by the camera lens is extracted using a pinhole, and the 0th order diffracted light is transferred to an objective. lens 2
1 to convert it into a plane wave, and convert this plane wave into a reflection type diffraction grating 22.
A diffraction image is formed on a detector 24 by an imaging lens 23 to perform spectroscopic measurements.

In addition, as shown in FIG.
5 may be used for spectroscopy.

FIG. 7 is a diagram showing another embodiment in which spectroscopy is performed using a Michelson interferometer.

In this embodiment, the linear component extracted by the pinhole is converted into a plane wave by the lens L1, and the Michelson interferometer 30
Inject it into the The light incident on the interferometer is divided into two parts by a half mirror 33, one part is reflected by a fixed mirror 31, the other part is reflected by a movable mirror 32, and the two parts are combined by the half mirror and detected by a detector 34. The movable mirror 32 is continuously moved, and as the optical path difference between the light reflected by the fixed mirror 31 and the movable mirror 32 changes between 0 and 1 wavelength, the intensity detected by the detector periodically changes. By Fourier transforming this signal, each wavelength component can be obtained.

FIG. 8 is a diagram showing another embodiment using a Michelson interferometer.

In this embodiment, an objective lens 43 is integrated into a Michelson interferometer 42, and light from a surface light emitter (not shown) is captured by a camera lens 41.

FIG. 9 shows another embodiment using a Michelson interferometer, and the only difference is that a Cassegrain optical meter 45 is used instead of the objective lens 43 in FIG. 8, and the other configurations are the same.

FIG. 10 is a diagram showing another embodiment in which a telescope and a Michelson interferometer are combined.

In this embodiment, the light from the surface light emitter S is taken in by a telescope 51, and a Fraunhofer diffraction image is formed at the pinhole position.

In this embodiment, since the focal length is sufficiently large, it is possible to increase the pinhole diameter for extracting the straight component.

In addition, in the above embodiment, an example of spectroscopy using a diffraction grating and a Michelson interferometer has been explained, but it is of course possible to use other dispersive spectroscopy methods such as a prism, a spatial interference type Fourier spectroscopy method, etc. be.

〔Effect of the invention〕

As described above, according to the present invention, since the slit image component corresponding to the width of the 0th order component or Oth order component of the Fraunhofer diffraction image is extracted using a pinhole or slit, two collections of the same F value can be extracted. By using optical lenses with different aperture ratios, it is possible to increase the density of spectral energy by increasing the diameter of the light beam taken in from the sample and decreasing the diameter of the light beam incident on the spectrometer.

[Brief explanation of the drawing]

Figure 1 is a diagram for explaining the coherent light selective spectroscopy method of the present invention, Figure 2 is a diagram for explaining a Fraunhofer diffraction image, and Figure 3 (A) is a diagram for explaining the reflection of a diffracted component by a pinhole. Figure 3 (B) is an explanatory diagram when a plane wave is incident on a pinhole, Figure 4 is a diagram showing another embodiment of the present invention using a Cassegrain optical system, and Figure 5 is a diagram showing a camera lens. Figure 6 is a diagram showing an example using a transmission type diffraction grating, Figure 7 is a diagram showing another example using a transmission type diffraction grating,
FIG. 8, FIG. 9, and FIG. 1O are diagrams showing other embodiments using a Michelson interferometer, and FIG. 11 and FIG. 12 are diagrams for explaining a conventional spectroscopic device. S...Surface light emitter, LO...Lens, P...Pinhole plate, Ll, L2...Lens, G...Transmission type diffraction grating, D...Detector. Figure 6 (A) Figure 1 Figure 2 Figure 4 Figure 5 Figure 10 Figure 11

Claims (5)

[Claims] (1) Pass light from the sample through an optical system to form a Fraunhofer diffraction image, and collect part or all of the 0th-order component of the Fraunhofer diffraction image, or a part or part of a slit-shaped component with the same width as the 0th-order component. A coherent light selection spectroscopy method characterized by extracting all of the light and performing spectroscopic measurements. (2) A first optical system having a predetermined aperture into which the light from the sample is incident, and a slit having the same width as the zero-order component or part or all of the zero-order component of the Fraunhofer diffraction image by the first optical system. a pinhole or slit having an aperture large enough to transmit part or all of the component, a second optical system having the pinhole or slit as a front focal point, and a spectrometer into which a plane wave from the second optical system is incident. What is claimed is: 1. A coherent light selective spectrometer comprising: selectively diffracting light from a pinhole or a slit; (3) In the apparatus according to claim 2, the first optical system includes a lens with a large light-receiving aperture, and the second optical system includes a lens with a small light-receiving aperture, and the F value of the first optical system is set to the second optical system. A coherent light selective spectrometer, which is equal to or lower than the F value of the system, converts the light flux from the sample that enters the first optical system into a small flux of light, and performs spectroscopy by increasing the energy per unit area. . (4) A coherent light selective spectroscopy device according to claim 2, wherein the spectroscope has a transmission type or reflection type diffraction grating. (5) A coherent light selective spectroscopy device according to claim 2, wherein the spectroscope has a Michelson interferometer.