JP2689707B2 - Spectrometer with wavelength calibration function - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spectroscopic measurement device for measuring a spectral distribution of light from a light source or reflected light of an object, and evaluates the light color and color rendering of the light source. It is used to evaluate the amount of effect on the spectrum, such as measuring the object color.

2. Description of the Related Art When evaluating the energy amount, light color, and color rendering of a light source or using spectroscopic measurement for measuring an object color, it is important to improve the accuracy of energy integration in the measurement rather than the wavelength resolution of the spectrum. That is, from the shape of the details of the wavelength distribution,
The issue is how to accurately capture it. This is realized by matching the spectral bandwidth half width of the used spectroscope with the measurement wavelength sampling interval. In a conventional dispersive element drive type monochromator, for example, in a prism monochromator, the dispersion curve and the wavelength scale match, so the machine width was measured at equal intervals. At this time, although the magnitude of the linear dispersion is considerably different between the short wavelength portion and the long wavelength portion, the difference in the dispersion between the adjacent measurement wavelength positions is not significantly changed. Further, in the dispersion element driving type diffraction grating monochromator, the dispersion curve and the wavelength scale are independent by introducing a sine bar mechanism. However, the dispersion of a diffraction grating monochromator is closer to a straight line than that of a prism, and it is difficult to mechanically correct the slit width according to the change in dispersion during spectroscopic measurement. Have been performing spectroscopic measurements.

Since the above-mentioned dispersive element driving type monochromator takes a long time for measurement, recently, a spectroscopic measuring instrument for measuring an optical spectrum from an object to be measured in a short time is used by combining a spectral dispersive optical system and a photodetector array. However, the mechanical interval of the light receiving element corresponding to the measurement sampling interval,
Since the dispersion is independent, the nonlinearity of the dispersion on the surface of the photodetector array is large, and the setting accuracy of the centroid wavelength of each array, that is, the accuracy of the wavelength scale is important.

In general, in a spectroscopic measurement device, a slight deviation in the alignment of the optical system causes a deviation in the value of the linear dispersion obtained from the design constant of the optical system. Therefore, the deviation from the theoretical wavelength graduation wavelength requires wavelength calibration. Until now, with this type of device, only one wavelength near the center of the measurement wavelength range has been calibrated with a bright line, etc., and the center of gravity wavelength of each array has been set by regarding the intervals of each array as equal intervals. The measurement error was large for applications such as color measurement.
In addition, when the emission lines of multiple wavelengths from the discharge lamp are guided to the spectroscopic measurement device and calibrated at each wavelength position, radiation from the discharge lamp other than that used for wavelength calibration, fluctuations in the output of the receiver array, etc. Was sometimes mistaken as an emission line of a wavelength to be used for calibration.

As an example, a combination of a concave diffraction grating and a photodiode array is shown.

The concave diffraction grating has the function of integrating a plane diffraction grating with a collimator mirror and a focusing mirror,
When the entrance slit of the concave diffraction grating is provided on a circle (Roland circle) whose diameter is the radius of curvature of the concave diffraction grating, the spectral dispersion image is formed on the Roland circle. For this reason, the spectrophotometer using the concave diffraction grating can simplify the optical system and can relatively reduce the change in the line dispersion. When using this kind of multi-channel spectrophotometer for photometric colorimetry, the relationship between the centroid wavelength of the spectral responsivity of each light receiving element and the dispersion characteristics, and the wavelength band characteristic of the spectral responsivity of each light receiving element and each light receiving element The interval (wavelength sampling interval) affects the measurement accuracy.

Engraved line density 300 lines / mm, blaze wavelength 500 nm, focal length f
A multi-channel spectrophotometer composed of a concave diffraction grating of = 200 mm and a silicon photodiode array (512 elements) is shown. FIG. 2 shows the optical system. Incident light is made incident from the entrance slit on the Rowland circle at 11.8 ° with respect to the center normal of the diffraction grating. In order to detect the diffracted light obtained by this in the normal dispersion region of the concave diffraction grating, the angle β between the center normal of the diffraction grating and the diffracted light is set to −4.8.
From + ° to + 2 °, and set the detection area between them.
At this time, a spectral dispersion image having a wavelength of 400 nm to 800 nm is obtained on the Rowland circle. The line variance on the center normal is 0.0
600 (mm / nm), the linear dispersion is 0.0 when β = -4.8 °.
Since it is 608 (mm / nm), the change in the line dispersion within the detection region is 1.3% or less in the wavelength range of 400 nm to 800 nm.
At this time, if the center of the silicon photodiode array is located on the center normal of the concave diffraction grating and located on the Rowland circle, from the value of the line dispersion at this position and the spatial interval (54 μm) of the element, The wavelength interval of each element near the center of the silicon photodiode array is 0.9 nm. Analytical determination of how the wavelength interval of each element changes from the center of the photodiode array to both ends is as follows. The wavelength spacing of each element is constant (0.9 nm) when the photodiode array is in contact with the Rowland circle, 0.5 mm inside the Rowland circle, and 0.5 mm outside the Rowland circle. The wavelength shift with respect to the above case is shown in FIG. As is clear from the figure, even when the photodiode array is in contact with the Rowland circle,
The center-of-gravity wavelengths of the elements are not arranged at equal wavelength intervals, and the deviation on the short wavelength side or the long wavelength side becomes large. This tendency becomes remarkable especially when the photodiode array deviates from the circumference of the Rowland circle. Therefore, in this type of multi-channel spectrophotometer, it is necessary to obtain the center-of-gravity wavelength of each element of the photodiode array.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention As described above, in general, the spectroscopic measurement device has a slight deviation in the alignment of the optical system, which causes a deviation in the value of the linear dispersion obtained from the design constant of the optical system. Deviation from the theoretical scale wavelength requires wavelength calibration. In particular, in a spectroscopic measurement device that combines a spectral dispersion optical system and a light receiving element array to measure the optical spectrum from the measurement object in a short time,
The nonlinearity of the dispersion on the surface of the light receiving element array is large, and the error of the wavelength scale causes the mismatch between the half bandwidth of the spectrum band and the sampling interval of the measurement wavelength, and the energy amount, light color, and color rendering of the light source can be evaluated. However, there is a problem that an error occurs when the spectroscopic measurement is used to measure the object color.

Means for Solving the Problems The present invention, in order to solve the above problems, a spectral dispersion means for spectrally dispersing light from a wavelength calibration bright line radiation source that outputs a plurality of bright lines of a measurement object or a specific wavelength, and From a photodetector array that converts the light from the spectral dispersion means into an electric signal, and a line dispersion determined by the spectral dispersion means,
A means for obtaining an address corresponding to the theoretical position of the element of the photodetector array in which the maximum photoelectric output is expected to be obtained for each bright line, and the photoelectric output for the bright line is the maximum in the neighboring elements. And a mechanical image of an image when the dispersed image of the incident bright lines is projected by the spectral dispersion unit before and after the device having the maximum photoelectric output as a center. Means that integrates the photoelectric output of an element that includes a certain width and that is in a range beyond that with the address of the element as a weighting factor, and an output of the array corresponding to a specific bright line with a weighting factor of 1
In the same manner, by dividing by the value of the integrated photoelectric output, a means for determining the address of the element of the photodetector array corresponding to the wavelength of each bright line, a plurality of calibration bright line wavelength,
The function of calibrating the wavelength scale of the device by obtaining the regression curve of the wavelength and the address from the corresponding actual address of the photodetector array and determining the respective centroid wavelengths for all the elements of the photodetector array. It is configured to have.

Action The present invention, by the above configuration, guides a plurality of bright lines of a specific wavelength obtained from the bright line radiation source to the spectroscopic measurement device, and from the line dispersion of the spectroscopic measurement device in advance, the maximum photoelectric output is obtained for each bright line. An address corresponding to the theoretical position of the element of the optical receiver array is obtained. The element when the photoelectric output to the bright line is the maximum in the element near that address, and the dispersed image of the incident bright line before and after that element is projected on the photodetector array by the spectral dispersion means. The photoelectric output is integrated with respect to an element which includes the mechanical width of the element and which exceeds the range, using the address of the element as a weighting coefficient, and the output of the array corresponding to a specific bright line is similarly weighted with a weighting coefficient of 1. Dividing by the integrated photoelectric output value, the address of the element of the photodetector array corresponding to the wavelength of each bright line is obtained. The centroid wavelength of each element of the photodetector array is obtained from the regression line of the bright line wavelength and the address of the photodetector array corresponding thereto.

In this way, in a spectrophotometer that combines a spectral dispersion optical system and a light-receiving element array to measure an optical spectrum from a measurement object in a short time, the non-linearity of dispersion on the surface of the light-receiving array is large. Even in such a case, the photometric colorimetric accuracy is improved by obtaining the regression curve of the address of each element and the wavelength by using the emission lines of a plurality of wavelengths and setting the centroid wavelength of each array. In particular, in the wavelength calibration with each bright line, it is possible to prevent the false recognition of the bright line due to stray light or noise of the spectroscopic measurement device, the emission of the lamp other than the bright line used for the calibration, and the accuracy of the wavelength calibration is improved.

First Embodiment A first embodiment of the present invention will be described with reference to the drawings. Second
The figure shows a multi-channel spectrophotometer composed of a concave diffraction grating 1 having a line density of 300 lines / mm, a blaze wavelength of 500 nm, and a focal length f = 200 mm and a silicon photodiode array (512 elements) 2.

Incident light is made incident from the entrance slit 4 on the Rowland circle 3 through the plane mirror 5 at 11.8 ° with respect to the center normal of the diffraction grating. In order to detect the diffracted light obtained by this in the normal dispersion area of the concave diffraction grating, the angle β between the center normal of the diffraction grating and the diffracted light is set from -4.8 ° to + 2 °,
The detection area is set in the meantime. At this time, the spectral dispersion image is
A wavelength of 400 nm to 800 nm is obtained on the Roland circle. The line dispersion on the center normal is 0.0600 (mm / nm),
Since the linear dispersion at β = -4.8 ° is 0.0608 (mm / nm), the change in the linear dispersion within the detection area is from 400 nm to 800 nm.
Within 1.3% up to nm. At this time, if the center of the silicon photodiode array is located on the center normal of the concave diffraction grating and located on the Rowland circle,
The value of the line dispersion at this position and the spatial spacing of the elements (54 μm)
Therefore, the wavelength interval of each element near the center of the silicon photodiode array is 0.9 nm.

The wavelength of the low-pressure mercury lamp is 404.66n as an emission line for wavelength calibration.
m, 435.84nm, 546.07nm, 578.01nm 4 mercury emission lines and neon lamp wavelengths 614.91nm, 639.48nm, 703.24nm
Use the bright line.

FIG. 3 shows a schematic diagram of the wavelength calibration means. The machine width of the entrance slit is 50 μm. As a result, the half-value width of the wavelength band of one element is 0.9 nm at the center of the measurement wavelength band, which is almost equal to the measurement wavelength interval. Therefore, the photometric and colorimetric error is reduced.

At this time, for example, the output of the silicon photodiode array 7 for the dispersed light of the mercury emission line having the wavelength of 546.07 nm is the first
It looks like the figure. First, the theoretical address calculation means 9 finds the linear dispersion from the constants of the optical system, and calculates the address of the element for the mercury emission line of the wavelength of 546.07 nm. Address 20 at this time
The maximum is around 0. Next, in order to obtain the address of the element having the maximum output among the elements having the output to the mercury emission line of the actual wavelength 546.07 nm, the element address of the element address 190 to 210 of the element address of the maximum value detecting means 10 is obtained. Examine the output.

The centroid wavelength calculating means 11 finds the centroid wavelength of each address. Now, when the address of the element is x = x _m , the output of the element is assumed to be the maximum value P (x _m ). The half-value width of the sensitivity wavelength band of the element is about 0.9 nm, and considering the skirt of the band, this width corresponds to the mechanical width of two elements. The center address Ad for the wavelength of 546.07 nm is obtained by using the following formula in the range of -3 to +3 with respect to the element address x _{m in} consideration of the distortion of dispersion.

_{A = -3 * P (x m} -3) -2 * P (x m -2) -1 * P (x m -1) + P (x m) + P (x m +1) + 2 * P (x m +2 ) + 3 * P (x _m +
3) B = P (x _m -3) + P (x _m -2) + P (x _m -1) + P (x _m ) + P (x _m +1) + P (x _m +2) + P (x _m +3) Ad = Similarly, for the six bright lines other than A / B, the center address is obtained, the regression curve of the wavelength and the address is obtained, and the centroid wavelength of each of the 512 light receiving elements is calculated. Thereby, wavelength calibration of the spectroscopic measurement device can be realized.

EFFECTS OF THE INVENTION As described above, according to the configuration of the present invention, in a spectroscopic measurement device or the like that combines a spectral dispersion optical system and a photodetector array to measure an optical spectrum from a measurement object in a short time, the Even if the dispersion nonlinearity is large, the emission curve of multiple wavelengths is used to find the regression curve between the address of each element and the wavelength, and the centroid wavelength of each array is set to determine the photometric accuracy. Is improved.

In particular, in the wavelength calibration with each bright line, it is possible to prevent the false recognition of the bright line due to stray light or noise of the spectroscopic measurement device, the emission of the lamp other than the bright line used for the calibration, and the accuracy of the wavelength calibration is improved.

[Brief description of the drawings]

FIG. 1 is an output characteristic diagram of a photodetector array with respect to a mercury emission line of a wavelength of 546.07 nm, FIG. 2 is a diagram showing an optical system of a multi-channel spectroscopic measurement apparatus of one embodiment of the present invention, and FIG. 3 is a wavelength calibration means. FIG. 4 is a schematic configuration diagram showing the deviation of the center-of-gravity wavelength of each light-receiving element of the light-receiving array from the equally-spaced wavelength scale. 1 ... Concave diffraction grating, 2 ... Silicon photodiode array, 3 ... Roland circle, 4 ... Injection slit, plane mirror, 6 ... Dispersed light, 7 ... Silicon photodiode array, 8 ... Charge transfer device, 9 ... Theoretical address calculating means, 10 ... Maximum value address calculating means, 11 ... Centroid wavelength calculating means.

Claims (2)

(57) [Claims] 1. A spectral dispersion unit that spectrally disperses light from a wavelength calibration emission line emission source that outputs a measurement target or a plurality of emission lines of specific wavelengths, and converts the light from the spectral dispersion unit into an electrical signal. A means for obtaining an address corresponding to a theoretical position of an element of the photodetector array, which is expected to obtain the maximum photoelectric output for each bright line, from the photodetector array and the line dispersion determined by the spectral dispersion means. And a means for obtaining the address of the element having the maximum photoelectric output for the bright line in the neighboring elements, and the element having the maximum photoelectric output as the center, before and after that.
The dispersed image of the incident bright lines includes the mechanical width of the image when projected onto the photodetector array by the spectral dispersion means,
In addition, the photoelectric output of an element falling within the range more than that is integrated by means of integrating the output of the array corresponding to the specific bright line with the weight coefficient of 1 and the photoelectric output value obtained by similarly integrating the photoelectric output with the address of the element. And a means for determining the address of the element of the photodetector array corresponding to the wavelength of each emission line, from a plurality of calibration emission line wavelengths, and the actual address of the photodetector array corresponding thereto, Obtain the regression curve of wavelength and address, for all elements of the photodetector array,
A spectroscopic measurement device with a wavelength calibration function, which has a function of calibrating the wavelength scale of the device by obtaining each centroid wavelength. 2. The spectroscopic measurement device with wavelength calibration function according to claim 1, wherein the wavelength width of the incident slit and the element wavelength interval of the photodetector array are set to be equal.