JP2005156343A - Spectroscopic device and optical filter for spectroscopic device - Google Patents

Abstract

Disclosed are a spectroscopic device and an optical filter for a spectroscopic device in which a light intensity difference in spectral characteristics generated by using a combination of various types of optical filters is eliminated.
A light beam that has passed through an entrance slit is dispersed by a concave diffraction grating into light having a short wavelength to a long wavelength, and an oblique direction is provided immediately before a photodiode array type detector that detects the light intensity of the dispersed light. An optical filter 4 formed by bonding a plurality of optical filters having different properties and having different properties is disposed. By selecting one having a refractive index close to the intermediate value of the refractive indexes of the optical filters 41 and 42 adjacent to the adhesive, the continuity of the transmittance of the optical filter is maintained, thereby generating a discontinuous change in spectral characteristics. Is suppressed.
[Selection] Figure 1

Description

  The present invention relates to a spectroscopic device and a spectroscopic device for performing quantitative / qualitative analysis of a sample from spectral characteristics obtained by dispersing composite light into continuous wavelength light via a dispersive element and measuring light intensity for each wavelength. The present invention relates to an optical filter for a spectroscopic device to be used.

  The dispersive element is an optical element such as a diffraction grating or a prism in which the output direction of the emitted light differs depending on the wavelength. A spectroscopic device that generates a spectrum representing a wavelength distribution from incident light by combining this dispersive element and an imaging optical system, and detects a light intensity at each wavelength of incident light by arranging a detector on a spectrum screen. Various things have been devised so far.

FIG. 4 shows a configuration when a concave diffraction grating polychromator, which is the simplest spectroscopic device, is used. The light beam incident from the entrance slit 1 is dispersed by the concave diffraction grating 2 and imaged on the spectral image plane on the detector 3. FIG. 5 shows the directions of incident light and outgoing light in the concave diffraction grating 2. The angle formed by the incident light B 1 and the normal L of the concave diffraction grating 2 is α, and the outgoing light B 2 of wavelength λ is the same as that of the outgoing light B 2. If the angle formed by the line L is β and the number of grooves of the concave diffraction grating 2 is N,
sin α−sin β = Nmλ (1)
Comprising (1) a relationship is established, lambda = lambda ₁ when beta = beta ₁ in the arrangement of FIG. _{5, λ} = _{λ 2} When beta = beta ₂ corresponds. Here, m is the diffraction order taking an integer value, and takes a negative value in the arrangement of FIG.

In the spectroscopic apparatus as described above, various optical filters are combined with the detector 3 in order to improve characteristics. For example, an optical filter for removing stray light caused by scattering on the surface of the dispersion element or the inner surface of the housing, an optical filter for correcting the wavelength dependence of detector sensitivity, or a diffraction grating type spectroscope An order separation filter or the like is used.
In the above equation (1), when λ = λ ₀ and m = m ₀ holds, if X is an integer, λ = λ ₀ / X, m = Xm ₀ naturally holds, and the same detector has a short wavelength. Light enters. The order separation filter is used for the purpose of preventing the short wavelength light from entering.

As shown in FIG. 4, the various filters as described above are generally arranged as needed just before the detector 3 and exhibit the intended function. In the case of an array type detector in which a plurality of detection elements are arranged, it is necessary to provide a window plate in order to improve environmental resistance, but an optical filter is often used instead of the window plate. At this time, when a plurality of optical filters 4a and 4b are used, a method of joining the vertical end faces to each other is adopted as shown in FIG.
JP-A-6-307933 JP-A-5-346349

The conventional spectroscopic device is configured as described above. However, when an optical filter is bonded to an array detector, the surface reflectance and internal transmittance differ depending on the physical properties of each optical filter. The total transmittance of the transmittance and the internal transmittance varies depending on the type of the optical filter. For this reason, in the wavelength band corresponding to the location where the optical filter is joined, as shown in FIG. 6A, a sudden change occurs in the output of the detector, that is, the measured light intensity. This phenomenon has a problem that in the spectroscopic device, a change with time and a change in the intensity distribution of the incident light beam occur, which increases the inaccuracy of the measurement data.
The present invention has been devised in view of the above problems, and a spectroscopic device and a spectroscopic device that eliminates a sudden change in light intensity in a wavelength band corresponding to a joint of an optical filter installed in front of an array detector. An object is to provide an optical filter for an apparatus.

In order to achieve the above object, the filter for a spectroscopic device of the present invention is disposed immediately before the detector of the spectroscopic device that uses a dispersive element to disperse the composite light into continuous wavelength light and detects the light intensity at each wavelength. The bonding surfaces of the optical filters having different properties are formed obliquely with respect to the arrangement direction of the detection elements, and bonded with an adhesive having a refractive index in the vicinity of the intermediate value of each refractive index of the optical filter.
In addition, the spectroscopic device of the present invention uses a dispersive element to disperse composite light into light of continuous wavelengths, and joins a plurality of optical filters having different properties arranged immediately before a detector that detects the light intensity of each wavelength. The optical filter is formed by forming the surface in an oblique direction with respect to the arrangement direction of the detection elements constituting the detector and bonding with an adhesive having a refractive index near the intermediate value of the refractive index of the adjacent optical filters. Yes.

  The spectral data acquired using the spectroscopic device of the present invention does not have a clear step that makes the spectral characteristics inaccurate. Therefore, the differential value calculated from this data and used for characteristic comparison or multiple times Quantization errors such as the relative intensity ratio calculated from the acquired data are reduced, and more accurate quantitative and qualitative analysis is possible.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of a spectroscopic device according to the present invention. The spectroscopic device includes an incident slit 1 that diffracts incident light that is composite light, and a concave surface for visible light that disperses the diffracted light diffracted according to the wavelength through the incident slit 1 into light having a wavelength of 380 to 780 nm. A detector 3 using a diffraction grating (polychromator) 2 and a self-scanning photodiode array consisting of 128 elements for detecting the intensity of the dispersed visible light, and an LPF filter on the short wavelength band side of the detector 3 An optical filter 4 formed by bonding a borosilicate glass 41 to be used and a sharp cut filter 42 that cuts 400 nm or less on the long wavelength band side, and a signal for generating and displaying a spectrum image by signal processing the output signal of the detector 3 The processing unit 5 is configured.

  The optical filter 4 is made by adhering a borosilicate glass 41 and a sharp cut filter 42 each having an oblique joining surface as shown in FIG. Are arranged on a detection element for detecting light having a wavelength of 500 nm to 600 nm. The borosilicate glass 41 has a refractive index of 1.52 and a transmittance of 92%, such as type BK7, and a transmittance of 92%, and the sharp cut filter 42 has a wavelength of 550 nm, such as type Y-44. An adhesive having a refractive index of 1.62 and a transmittance of 89% is used, and the adhesive 43 for bonding them has a refractive index of 1.56, that is, between the refractive indexes of the borosilicate glass 41 and the sharp cut filter 42. Those having a refractive index are used.

In order to explain the characteristics of the optical filter 4 simply, the transmittance of the borosilicate glass 41 is K ₁ , the transmittance of the sharp cut filter 42 is K ₂ , the gradient of the slope of the joint is k, and the wavelength band where the gradient exists Is 100 nm (500 nm to 600 nm), the average transmittance K _X at the position of x in the horizontal direction from the starting point 500 nm (point P) of the gradient is expressed by the following equation.
K _X = K ₁ + (K ₂ −K ₁ ) x / 100 (2)
When the characteristics represented by the equation (2) are expressed on the coordinates where the horizontal axis represents the wavelength band and the vertical axis represents the light transmittance, the result is as shown in FIG. In the wavelength band of 100 nm up to the point, the transmittance K _X maintains the continuity of the transmittance.

  The signal processing unit 5 includes an AD converter 51 that AD-converts analog electrical signals that are sequentially output from the self-scanning photodiode array that constitutes the detector 3 at regular intervals, and performs arithmetic processing on this output to perform wavelength-specific processing. A CPU 53 that calculates the light intensity and converts it into a video signal for a spectral characteristic image, a display unit 56 that displays the image, an operation unit 57 that performs operation commands such as analysis start / end, and the CPU 53 and the outside An input interface 52 for performing input / output processing and an output interface 55 are configured.

  The analysis operation by the spectroscopic device is performed in the following procedure. In FIG. 1, when the composite light enters the entrance slit 1, the composite light is diffracted and spreads, and is irradiated to the concave diffraction grating 2. Since the diffraction angle with respect to the incident angle of the light varies depending on the wavelength as shown in the equation (1), the diffracted light spreads from a short wavelength to a long wavelength and enters the detector 3 via the optical filter 4. Since the incident light passes through the optical filter 4 having a continuous transmittance with respect to the wavelength as shown in FIG. 2B, an electric signal proportional to the light intensity for each wavelength is generated without causing a sudden change. Converted.

  The electrical output signal of each photodiode of the detector 3 is sequentially sent to the AD converter 51 in the order of wavelengths by self-scanning, and is AD-converted, and then taken into the CPU 53 via the input interface 52 and stored in the memory 54. The light intensity for each wavelength is calculated by the intensity calculation formula, and the measurement data is sent to the display unit 56, and a spectrum characteristic image as shown in FIG. 6B is obtained. In this spectral characteristic image, the continuity of the transmittance of the optical filter 4 is maintained, so that the conventional light intensity step as shown in FIG. 6A does not occur. Thereby, since the ratio of the amount of light that passes through each of the bonded filters and enters the detector 3 continuously changes, the signal intensity change between the detectors becomes gradual, and the inaccuracy of the data is reduced. be able to.

  The present invention is not limited to the embodiment. For example, the optical filter 4 is composed of two types of filters, but the optical filter 6 (optical filters 61 to 64 shown in FIG. 3 is combined). Can also be used. Further, as a spectroscopic device, a concave diffraction grating is used to disperse incident light into a wavelength sequence. However, the present invention is not limited to this. For example, a fasty-evert mount method combining a concave mirror and a diffraction grating, a collimator, a focus mirror, and a plane It is also possible to use spectroscopic means such as a Czerny-Turner mount method combined with diffraction gratings, or to use a parallel readout type as a photodiode array.

It is a schematic block diagram of the spectroscopic device by an Example. It is the block diagram (a) and the transmittance | permeability characteristic view (b) of the optical filter by an Example. It is a block diagram of the optical filter by another Example. It is a schematic block diagram of the conventional spectroscopic device. It is a figure which shows the direction of the incident light and outgoing light in a concave-surface diffraction grating surface. It is the spectral characteristic image (a) of the conventional spectroscopic device, and the spectral characteristic image (b) of the spectroscopic device by an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Entrance slit 2 Concave diffraction grating 3 Detector 4 Optical filter 4a Optical filter 4b Optical filter 41 Borosilicate glass 42 Sharp cut filter 43 Adhesive 5 Signal processing part 51 AD converter 52 Input interface 53 CPU
54 Memory 55 Output Interface 56 Display Unit 57 Operation Unit 6 Optical Filter B1 Incident Light B2 Outgoing Light L Normal

Claims (2)

Multiple optical filters with different properties arranged just before the detector of the spectroscopic device that disperses the composite light into continuous wavelength light using a dispersive element and detects the light intensity at each wavelength, constituting the detector Adjacent optical filters having a joint surface formed in an oblique direction with respect to the arrangement direction of the detection elements to be bonded are bonded with an adhesive having a refractive index in the vicinity of an intermediate value of each refractive index of the optical filter. An optical filter for a spectroscopic device. In a spectroscopic device that uses a dispersive element to disperse composite light into light of continuous wavelengths and detects the light intensity at each wavelength, the joint surface of a plurality of optical filters having different properties arranged immediately before the detector And an optical filter formed by bonding with an adhesive having a refractive index in the vicinity of an intermediate value of each refractive index of adjacent optical filters. A spectroscopic device.

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