JPS6341411B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multi-wavelength spectrometer that can measure a wide wavelength range at once.

In a multi-wavelength spectrometer, which uses an imaging device such as a photodiode array in which minute light-receiving elements are arranged one-dimensionally to measure the spectra of a diffraction grating at once, each order of diffracted light overlaps. It is necessary to discriminate the diffracted light, and a filter with a single characteristic is usually used to remove the diffracted light of unnecessary orders. However, this method cannot cover a wide wavelength range at once, and measurements over a wide wavelength range had to be carried out in two or more separate measurements.

Therefore, the present invention was made with the object of obtaining a multi-wavelength spectrometer that can cover a wider wavelength range at once than the conventional one.

First, we will discuss the reason why conventional multi-wavelength spectrometers have been unable to cover a wide range of wavelengths at once. FIG. 1 shows the wavelength dispersion of the first-order diffracted light and the second-order diffracted light of a diffraction grating, where a is the first-order diffracted light and b is the second-order diffracted light. Since the width of the factorial imaging device in the scanning direction is narrow, it is better to use first-order diffracted light rather than second-order diffracted light when trying to fit a spectrum of a wide wavelength range within that width. In Figure 1, if the first-order diffracted light covers the range from 400nm to 800nm, the width of the image sensor is B.
However, if second-order diffracted light is used, twice the width is required. Therefore, if we decide to use the first-order diffracted light, the second-order diffracted light of 200 to 400 nm overlaps and becomes a nuisance. For this purpose, you can use a low-pass filter that cuts out light with a wavelength of 400 nm or less, but it will cut out 100% of the wavelength of 400 nm or less.
There is no filter with completely step-like characteristics that transmits 100% of the above points, so if you try to measure 400nm light, the longest wavelength that the filter will completely cut out will be 400nm or less. Therefore, the second-order diffracted light around 400 nm overlaps around 800 nm at the long wavelength end. Therefore, it is not possible to set the measurable wavelength range to be more than twice the wavelength at the short wavelength end, and in fact, it is impossible to realize a wavelength range that is twice as large as the wavelength at the short wavelength end.

The present invention provides a multi-wavelength spectrometer that can set the wavelength range that can be measured at one time to twice or more the short wavelength end wavelength.

The multi-wavelength spectrometer of the present invention is characterized in that a filter whose characteristics change in the wavelength dispersion direction of the diffraction grating is disposed in contact with the light-receiving surface of the image sensor. The present invention will be explained below with reference to Examples.

FIG. 2 is a plan view of an embodiment of the multi-wavelength spectrometer of the present invention. 1 is an entrance slit, 2 is a collimator mirror, 3 is a plane diffraction grating, 4 is a camera mirror, and 6 is a one-dimensional image sensor, and a filter 5 is arranged in contact with the light receiving surface of this element. This filter is the first
As shown in Figure C, this is a bandpass interference filter in which the central transmission wavelength changes in the wavelength dispersion direction of the diffraction grating, and is made by gradually changing the thickness of the vapor deposited film on the substrate in that direction. With this configuration, in the spectral image on the light-receiving surface of the image sensor 6, when the wavelength is around 800 nm, the filter has the characteristic of a bandpass filter that transmits around 800 nm, and all light of second-order diffracted light or higher is cut out. Similarly, in the vicinity of 400 nm in the spectrum, light other than those with wavelengths around 400 nm are cut out, so interference from secondary and higher order diffracted light is removed.

The characteristics of the filter 5 do not need to change continuously as described above, and the thickness of the deposited film may be changed stepwise to form several types of bandpass filters as shown in FIG. 3 on one substrate. They may be formed in parallel on top. In this case, it is better for each partial filter to have broad characteristics. Furthermore, as shown in FIG. 4, a filter whose transmission characteristics change in two stages may be used. In other words, there is a dramatic wavelength difference of 1/2 of the wavelength that should be transmitted between the wavelength that should be transmitted and the wavelength that should be cut at one point on the spectral image, so the transmission characteristics at each point on the filter are as follows. This is because it can be extremely broad.
Therefore, a two-stage low-pass filter may be used instead of the two-stage band-pass filter. If such a filter is to cover the wavelength range of 400 to 800 nm, for example, a UV-opaque ordinary glass substrate with a wavelength of 500 nm or less on the long wavelength side from the center (half of the long wavelength side of the spectral image when installed on the image sensor) It may be something with a coating that cuts it. Further, by utilizing the spectral sensitivity characteristics of the image sensor itself, a coating similar to that described above may be applied to a quartz substrate using a material that is insensitive to ultraviolet rays.

In the above explanation, it may be possible to place several filters with different characteristics adjacent to each other, but if this is done, the spectral image will be disturbed at the joint of the filters, so It is desirable that the characteristics change at the top.

The multi-wavelength spectrometer of the present invention has the above-mentioned configuration,
By placing filters with different characteristics depending on location on a single board in contact with the light-receiving surface of the image sensor,
Since unnecessary light at each point on the spectral image plane is cut out, the measurement wavelength range is no longer limited when using a filter with a single characteristic, and a wide wavelength range can be measured at once. When multiple filters are stacked adjacent to each other or shifted in a stepped manner, the spectral image is disturbed due to the disturbance of the optical path at the filter boundary, the level of stray light increases due to scattered light, and the step-like shape of the filter thickness A good spectral image can be obtained without any deviation of the focal plane of the camera mirror due to the change.

[Brief explanation of drawings]

Fig. 1 is a graph showing the wavelength distribution according to the diffraction order of the spectroscopic spectrum by the diffraction grating, Fig. 2 is a plan view of an embodiment of the device of the present invention, and Figs. 3 and 4 are the phases of the filter that can be used in the present invention. 3 is a graph showing characteristics of different examples. 1...Incidence slit, 2...Collimator mirror, 3...Plane diffraction grating, 4...Camera mirror, 5...Filter, 6...
One-dimensional image sensor.

Claims (1)

[Claims] 1. A one-dimensional image sensor is placed in a spectral image of the wavelength range to be measured of the light of the diffraction order to be measured by the diffraction grating, and in front of the light receiving surface of this image sensor, at each position of the above spectral image. , one which has different transmission characteristics depending on the location, so as to transmit light in a certain wavelength range including the light of the diffraction order to be measured, and block diffracted light of orders other than the order to be measured at that position. A multi-wavelength spectrometer characterized by the arrangement of filters.