JPH034130A - Spectrophotometer - Google Patents

Abstract

PURPOSE:To shorten the time for measurement by providing arithmetic means for calculating the shape of spectra by specific equation from a change in respective picture element outputs of a photodetector during the movement of spectra. CONSTITUTION:The movement of the spectral image by about 50mum picture element component on the photodetector 3 by 10 deg. oscillation of a glass plate 4 if the average inclination with a central optical path toward the center of a diffraction grating 1 is previously and adequately adjusted through an inlet slit 2 of a quartz glass plate 4. A pulse motor 7 is driven and the output of the photodetector 3 is taken in via an interface 9 at every movement of the spectral image by 10mum, i.e. 0.2nm in wavelength. The computation to calculate the spectral intensity at every 0.2nm wavelength after the end of the spectral movement by 1nm is executed by the equation {where (i) is a picture element number (1 to n); (k) is sampling order; pik is the k-th sampling data of the i-th picture element; S(lambdai, k)is the spectral intensity at wavelength lambdai, k}.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a spectrophotometer using an array of linear light receiving elements.

(Prior Art) There are two types of spectrophotometers: a wavelength scanning type and a type that uses a linear light-receiving element with one-dimensional positional resolution and does not perform wavelength scanning. The former has excellent wavelength resolution, but it takes time to measure a predetermined wavelength range. Since the latter measures light at each wavelength on the spectrum simultaneously, it has the advantage that the time required to measure a predetermined wavelength range is significantly shorter than the former, but the wavelength resolution is lower than the former. A spectrophotometer using a linear light-receiving element takes advantage of its high speed and is used to track temporal changes in a sample or as a detection means for chromatography.

(Problems to be Solved by the Invention) As mentioned above, a spectrophotometer using a linear photodetector has the characteristic that the measurement time is short, but the wavelength resolution is limited by the number of pixels of the linear photodetector. There is a problem that it is lower than that of a scanning type spectrophotometer. The present invention aims to improve the wavelength resolution of a spectrophotometer using a linear light receiving element.

(Means for Solving the Problem) A means for moving the spectral image on the linear light receiving element in the wavelength dispersion direction by one unit element (pixel) of the light receiving element is provided in the optical system of the spectrometer, and A calculation means was provided for calculating the shape of the spectrum by solving the equation (1) from the change in the output of each pixel of the light receiving element.

(Operation) Each pixel on the light receiving element is numbered from 1 to n from the end. With the spectral image on the light receiving element at the reference position, S(λ)
shall be. This reference position is the position of the spectral image relative to the light receiving element at the start of movement when the spectral image is moved. Each wavelength of the point equally divided in the spectral dispersion direction e on the i-th pixel at this reference position is λil+λ12...
λie (λil is the wavelength at one end of the same pixel,
(see figure). When determined in this way, the output Fil of each pixel of the light receiving element when the spectral image is at the reference position is pH-
S(λ11)+SCλ12)+・S(λN)P21-
S(λ21)+... Pil=S(λ if) 10−5(λ ie) The output of each pixel when the spectral image is moved by -step, that is, 1/e of the pixel width, is pH, P21 , . . , and the output of the i-th pixel when it is generally moved in steps is expressed as Pik, as shown in the following equation. This is a concrete representation of the above formula (1).

pH-5(λII)+5(λ12)+...+S(λI
t') Pl2- S(λ12)+...+S(
λ1 e )+S(λ21)2l- 5(λ21) 10... Pik-5(λ, k)+S(λi, k+l)-+S(λ
ik+e), and e measurement values are obtained for each pixel and eXn measurement values for all pixels, and for these measurement values,
The above formula (1) holds true. This formula has eXn formulas,
The number of unknowns S(λik) varies from wavelength λll to λn
There are eX (n+1)-1 pieces up to e, and at this moment (1
) cannot be used to calculate S(λik).

However, in practice, it is possible to properly design the optical system so that the spectral image does not exist over the entire length of the light receiving element, and there are pixels with zero incident light at the end of the light receiving element. Now, if the spectral image is at the reference position, the third
Assume that the output of the first pixel is 0 as shown by the solid line in the figure. That is, it is assumed that the spectrum is formed as shown in FIG. In this case, both the left and right sides of the first equation (10) are O. Next, when the spectral image is moved one step to the left, the spectrum becomes as shown by the dashed line in Figure 3, and the output P12 of the first pixel is S(λ11) and S(
λle) is O, so Pl, 2=S(λ21)
becomes. If we move further l steps to the left, Pl3 in the third equation (1) becomes S(λ21) + S(λ22), but since S(λ21) has already been found, S(λ22
) can be found. In the same way, S(λ23)...S
(λik)... can be determined and carried out.

(Example) FIG. 1 shows a spectrophotometer according to an embodiment of the present invention.

1 is a concave diffraction grating, 2 is an entrance slit, and 3 is a one-dimensional photodiode array as a light receiving element. These three elements are fixedly arranged as shown in the figure, so that a spectral image is formed on the light receiving element 3. A quartz glass plate 4 is inserted into the optical path between the entrance slit 2 and the diffraction grating 1. This quartz plate is rotatably supported within the plane of the figure with a shaft 5 outside the optical path as a fulcrum, and an arm extending from the end opposite to the shaft 5 is brought into contact with a cam 6. 6, it can be swung within an angular range of about 10 degrees. The light receiving element has a width of about 25 μm per pixel and is made up of 512 elements, on which a spectral image in a wavelength range of 200 nm to 700 nm is formed. Therefore, the wavelength range per pixel of the light receiving element is 1 nm, which is the wavelength resolution of this type of spectrophotometer in the conventional sense. The quartz glass plate has a thickness of about 1 mm and can be oscillated over a range of 10' as described above. By appropriately adjusting the average inclination of the entrance slit 2 of the quartz glass plate with respect to the central optical path toward the center of the diffraction grating, the spectral image can be divided into one pixel on the light receiving element 3 by swinging the quartz plate 4 by 10°. It can be moved approximately 50 μm per minute. 7 is a pulse motor that drives the cam 6. As shown in FIG. 4, when the light beam is moved by swinging the quartz glass (n=1.46), the swing angle and the amount of movement are practically proportional at low angles. 8 is a III control circuit that drives the pulse motor 7, receives the output of the light receiving element 3 via the interface 9 every time the spectral image moves on the light receiving element by 10 μm, that is, 0.2 nm in wavelength, and receives the output of the light receiving element 3 through the interface 9; After finishing the spectrum movement,
Spectral intensity calculation calculations are performed for each wavelength of 0.2 nm, and the results are stored or displayed.

The means for moving the spectral image on the light receiving element is arbitrary, and a piezoelectric element or an electromagnetic vibrator may be used to passively move the quartz glass plate. A mirror may be used instead of the quartz glass plate. Alternatively, the light receiving element itself may be reciprocated in the wavelength dispersion direction, and a piezoelectric element may also be used as the driving element in that case.

Although omitted in the above explanation, since the sensitivity of image sensors such as photodiode arrays varies from pixel to pixel, and to correct for stray light, it is necessary to measure the overall spectral characteristics of the light source and photodetector without a sample in advance as described above. When measuring a sample, the above-mentioned spectrum calculation operation is performed using data obtained by dividing the output of each pixel by the above-mentioned spectral characteristics for each pixel. Further, in the embodiment, a 512-pixel element is used, but the device is not limited to this, and 256 pixels or 102 pixels are used.
Needless to say, elements such as 412 elements can be used. (Effect of the invention) A type of spectrophotometer that measures a spectral image at once using an image sensor without performing wavelength scanning using a dispersive element requires -1 measurement time compared to a wavelength scanning type spectrophotometer. Although it has a characteristic that the time is extremely short, according to the present invention, in addition to this characteristic, high wavelength resolution can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a plan view of an apparatus according to an embodiment of the present invention, FIG. 2 is an explanatory diagram of the operation of the present invention, FIG. 3 is also an explanatory diagram of the operation, and FIG. This is a relationship graph with deviation. l... Diffraction grating, 2... Exit slit, 3... Light receiving element (for example, photodiode array), 4... Quartz glass plate, 5... Support shaft, 6... Cam, 7... - Motor, 8...control circuit, 9...interface. Me4 Mouth

Claims (1)

[Claims] In a spectrophotometer of a type that forms a spectral image on a light-receiving element with one-dimensional positional resolution and obtains spectral data from the output of each unit element (hereinafter referred to as a pixel) of the light-receiving element. , a means for relatively moving a spectral image by one pixel on the light-receiving element, and sampling the output of each pixel of the light-receiving element multiple times during the spectral image movement period, and extracting l×n pieces of data from the sampled data. A spectrophotometer characterized in that it is provided with arithmetic means for calculating the shape S(λ) of a spectral image by solving the following equation (1). Pik=S(λi,k)+S(λi,k+1)+...
S(λi, k+l)...(1) However, i is the pixel number (
1 to n), k is the sampling order (1 to l), Pik is the k-th sampling data of the i-th pixel, and S(λi
, k) is the spectral intensity at wavelength λi.