CN108489609A - A kind of FTIR measures the wide range bearing calibration of photodetector response - Google Patents

Abstract

The invention discloses the wide range bearing calibrations that a kind of FTIR measures photodetector response, this method is using based on the pyroelectric detector with wide spectral range flat response as FTIR spectrum instrument standard configuration, it obtains the detector and amplifying circuit and the response under different scanning speed is combined to selected light and beam splitter, extract related data and fit the frequency response characteristic of the detector and amplifying circuit.The original output characteristics combined to specific light source and beam splitter using this frequency response characteristic is corrected to get to its actual output characteristics.Using this reality output characteristic after correcting as background spectrum, you can the photodetector original response spectrum to measuring gained carries out reference operation, the photodetector real response spectrum after being corrected.It is the standard configuration of FTIR spectrum instrument in view of pyroelectric detector and is responded with wide range, thus the method is pervasive and wide range, different light sources and beam splitter combination suitable for various FTIR spectrum instrument.

Description

A Broad Spectrum Calibration Method for FTIR Measuring Photodetector Response

technical field

The invention belongs to the field of semiconductor optoelectronic spectroscopy, and specifically relates to a universal method for correcting the response of a photodetector measured by a Fourier transform infrared (FTIR) spectrometer in a wide spectral range.

Background technique

Semiconductor photodetectors (PDs) and their focal plane arrays (FPAs) have important applications in many fields, and their response spectra are of great concern in all these applications. Conventional PD or FPA has a continuous response wavelength range, within which the size of the response will change, that is, the responsivity has a spectral distribution, this spectral distribution or response spectrum needs to be obtained through actual measurement, and has a series of advantages The Fourier transform infrared (FTIR) spectrometer has become the instrument of choice for measuring PD or FPA devices, especially in the infrared band.

Although the photocurrent spectrum of the detector directly measured by the FTIR spectrometer contains its spectral response information, it is not the actual response spectrum of the detector, and in many cases is far from the actual response spectrum, which is mainly due to the output of the instrument itself. The characteristics (including light source and beam splitter and other components) are very uneven, which itself also has a specific spectral distribution. In order to solve this problem, people have also developed related correction methods called calculation instrument function correction method, standard detector transfer correction method, etc., so as to obtain the actual response spectrum of the detector. These have achieved certain results, but there are still many problems. For example: for the calculation instrument function correction method, using the black body radiation formula to simulate the output of the infrared light source, it is necessary to set a black body radiation temperature, so that the infrared light source is not an ideal black body with a single temperature, and the setting of this temperature is artificial. It is not obtained through actual measurement. On the other hand, the temperature of the actual infrared light source must have a distribution range, which is difficult to simulate with a single temperature; in addition, the response characteristics of the beam splitter required for the calculation of the instrument function correction method are not actually measured, and these are inevitably introduced. Certain error. Another example: the basis of the standard detector transfer correction method is based on the calibrated standard detector, so the correction range can only be limited within the response range of the standard detector, and different wave bands require different standard detectors. The connection is also difficult, which limits the application in many occasions. Quantum photodetectors are still under development, and some devices with wide-spectrum response have also appeared, such as InGaAs detectors whose response extends to the visible light band. Characterizing the spectral response of such broadband devices is a problem that must be solved.

Contents of the invention

Based on the problems mentioned above, the present invention innovatively proposes to provide a universal method for correcting the photodetector response measured by Fourier transform infrared (FTIR) spectrometer in a wide spectral range, which can realize the wide-band range The photodetector inside is corrected for spectral response.

The specific operation steps of the correction method of the present invention are:

1) By measuring the response of the pyroelectric detector and amplifier circuit to the combination of the selected light source and beam splitter at different scanning speeds, and then extracting relevant data to fit the analytical frequency response characteristics of the detector and amplifier circuit;

2) Correct the original output characteristics of the specific light source and beam splitter combination according to the analytical frequency response characteristics of the pyroelectric detector and the amplifier circuit obtained in step 1), so as to obtain the FTIR spectrometer under this specific light source and beam splitter combination the actual output characteristics, i.e. the actual background spectrum;

3) According to the actual output characteristics of the corrected spectrometer obtained in step 2) as the background spectrum, the original response spectrum of the measured photodetector is referred to to obtain the corrected actual response spectrum of the photodetector.

Given that the pyroelectric detector is a standard configuration of FTIR spectrometers and has a broad spectral response, this method can be applied to various FTIR spectrometers, and is suitable for different light source and beam splitter combinations covering a wide spectral range, so it is universal and broad-spectrum. In order to be suitable for the mid-infrared band, the standard pyroelectric detector of the FTIR spectrometer is now usually a DTGS detector with a KBr window, hereinafter referred to as the DTGS detector. As a thermal detector, the DTGS detector itself has a flat spectral response independent of wavelength, and the transmittance of the KBr window in the entire mid-infrared band as well as the near-infrared and visible light bands is also flat, so the DTGS detector It can be considered as a device whose response is independent of wavelength, but its response is directly related to the frequency of the optical signal.

For further illustrating the present invention, Fig. 1 has shown the original background spectrum of the FTIR spectrometer that adopts DTGS detector and amplifying circuit to measure under different scanning speeds under specific light source and beam splitter combination, and hollow square among the figure is follow-up fitting selected data points. It can be seen from Figure 1 that as the scanning speed increases, the output measured by the DTGS detector/amplifier combination at each wave number decreases, but the actual output should remain unchanged, which is the result of the DTGS detector and amplifier circuit. caused by the frequency response. For the measurement results in Fig. 1, in order to cover a wide frequency range, relative response data were extracted at the wave number points of 9000cm-1, 3000cm-1 at the low frequency end, and 15000cm-1 at the high frequency end for fitting. The three wavenumber points have better representation, and also avoid the error that may be caused by the water vapor absorption band. Based on the extracted data at 9000cm-1, the data of the low-frequency end 3000cm-1 and the high-frequency end 15000cm-1 were lifted as a whole to make them coincide with the trend of the data in the middle frequency range of 9000cm-1. Using the Fourier frequency fF, the dynamic The linear relationship fF=2vν between mirror scanning speed v and wave number ν, a set of data for fitting with extended high and low frequency ends is obtained, as shown in Figure 2. The analytical fitting curve shown in Fig. 2 can be obtained by nonlinear fitting to this group of data, and a relatively simple reciprocal second-order polynomial fitting can have a good effect. Using the fitting function obtained in Figure 2, the instrument output (as shown in Figure 1) at a specified scanning speed can be corrected, that is, the reference calculation can be performed to obtain the actual output characteristics of the instrument, that is, the actual background spectrum.

After obtaining the actual background spectrum at a certain scanning speed, the reference calculation is performed on the original spectrum of the photodetector measured at the same scanning speed, that is, the actual response spectrum of the photodetector after correction is obtained, as shown in Figure 3 shown. For FTIR spectrum measurement, measurement and calculation are routinely performed in wavenumber coordinates, and the conversion of wavenumber coordinates into wavelength coordinates is still performed conventionally. Fig. 3 also shows the detector response spectra obtained by sampling other calibration methods, that is, the so-called standard spectral data for comparison.

The advantages of the present invention are:

A. The correction methods of the present invention are all based on measured data, and the only assumption is that the response of the pyroelectric detector has nothing to do with the wavelength, which is also consistent with the actual situation, so a good correction effect can be obtained.

B. The correction method of the present invention only needs to carry out a group of measurement fittings to the same spectrometer (including the DTGS detector of its configuration) and can easily obtain the frequency response characteristics of the required DTGS detector and amplifying circuit, and the instrument thereafter The calibration steps are all based on the background spectrum obtained from this feature and are therefore easy to operate.

C. The corrected background spectrum also contains interference such as water vapor absorption, so using this as a reference can basically eliminate the corresponding interference in the final response spectrum.

D. The correction method of the present invention is universal because its principle is applicable to different combinations of light sources and beam splitters, and can cover a wide range of wavelengths;

Description of drawings

Figure 1 shows the original background spectrum of the FTIR spectrometer under the combination of tungsten-halogen lamp (white light) light source and quartz beam splitter measured by DTGS detector and its supporting amplifier circuit at different scanning speeds, and the hollow squares in the figure are subsequent fitting selected data points.

Figure 2 shows the frequency response characteristics of the DTGS detector and amplifier circuit obtained by fitting the data points extracted from Figure 1.

Fig. 3 is the original photocurrent spectrum (thin solid line) of the measured Si and InGaAs detector and the actual response spectrum (thick solid line) of the detector corrected by the method of the present invention; among the figures, the dots are the two detectors The calibration data is also the standard data for comparison, and the data in the figure have been normalized.

Detailed ways

The specific embodiment of the present invention will be described in detail below in conjunction with the accompanying drawings.

Example 1: Wavelength Extended InGaAs Detector

As shown in the lower part of Fig. 3, the original photocurrent spectrum test is carried out for a wavelength-extended InGaAs detector with existing standard spectral data, and the response spectrum correction is carried out by using the correction method of the present invention. The long-wave cut-off wavelength of this device is about 2.5 μm. It is a front light-incoming detector, and the response of the short-wave end extends to the visible light band. Therefore, a combination of a tungsten-halogen lamp (white light) light source and a quartz beam splitter is used in the measurement to make the spectrometer more efficient. Strong short-wave output, thus covering a wide spectral range from mid-infrared short-wave end to visible light. Under fixed aperture and gain parameters, firstly change the scanning speed (such as 0.1581cm/s to 1.8988cm/s, a total of 7 levels) to measure a set of original background spectra (as shown in Figure 1). A large number of scans (such as 64 times); for detector measurement, because it generally does not contain fine spectral information, a lower resolution (such as 16cm-1) can be used to shorten the measurement time; and then under the same conditions to scan Speed (such as 0.4747cm/s, can actually be selected according to needs) to measure the original photocurrent spectrum of this wavelength extended InGaAs device, and then extract the required data from this group of original background spectrum test data for the frequency of DTGS detector and amplifying circuit Characteristic fitting to obtain the analytical parameters of its frequency characteristics. Based on this frequency characteristic, the original background spectrum at the scan speed of 0.4747cm/s is used for reference calculation to obtain the actual background spectrum, and then the actual background spectrum is used for reference calculation for the original response spectrum of the wavelength-extended InGaAs device, that is, the actual background spectrum of the device is obtained. Response spectrum, and finally convert the spectrum under the wavenumber coordinates into wavelength coordinates, that is, the corrected actual response spectrum shown in the thick line at the bottom of Figure 3 is obtained. The thin line in the figure is the original spectrum obtained from the measurement, and the dot is the standard spectrum of the device , for comparison. In this process, attention should be paid to the data quality so that the operation can be carried out and the results are reliable. For the low-quality data caused by the low output of the instrument at the high-frequency end (and low-frequency end) and the He-Ne laser wavelength inside the spectrometer (such as 15770-15820cm -1 interval) can be truncated or deleted. Since this spectral test only involves the relative value of the response, there is no need to pay attention to the absolute value of the data, and the multiplication, division and normalization operations can be performed at any time to facilitate data processing.

Embodiment 2: Si detector

As shown in the upper part of Fig. 3, the original photocurrent spectrum test is carried out for a Si detector with existing standard spectral data, and the response spectrum correction is carried out by using the correction method of the present invention. The long-wave cut-off wavelength of this detector is about 1 μm, and the response of the short-wave end extends to the visible light band. Therefore, the combination of the halogen tungsten lamp (white light) light source and the quartz beam splitter is still used in the measurement, so that the spectrometer has a strong Shortwave output. Under fixed aperture and gain parameters, first change the scanning speed (such as 0.1581cm/s to 1.8988cm/s7 files) to measure a set of original background spectra (as shown in Figure 1). To ensure data quality, more The number of scans (such as 64 times); for detector measurement, since it generally does not contain fine spectral information, a lower resolution (such as 16cm-1) can be used to shorten the measurement time; and then under the same conditions at a fixed scanning speed ( Such as 0.4747cm/s, which can be selected according to actual needs) Measure the original photocurrent spectrum of this Si detector, and then extract the required data from this group of original background spectrum test data to fit the frequency characteristics of the DTGS detector and the amplifier circuit , to obtain the analytical parameters of its frequency characteristics (note that this process is exactly the same as in Embodiment 1, so the same instrument only needs to perform this operation once). The actual background spectrum is obtained by performing reference calculation on the original background spectrum at a scanning speed of 0.4747cm/s with this frequency characteristic, and then the actual background spectrum is used to perform reference calculation on the original response spectrum of the Si detector, that is, the actual background spectrum of the detector is obtained. Response spectrum, and finally convert the spectrum under the wavenumber coordinates into wavelength coordinates, that is, the corrected actual response spectrum shown in the thick line in the upper part of Figure 3 is obtained. The thin line in the figure is the original spectrum obtained from the measurement, and the dot is the standard spectrum of the device , for comparison. In this process, attention should be paid to the data quality so that the operation can be carried out and the results are reliable. For the low-quality data caused by the low output of the instrument at the high-frequency end (and low-frequency end) and the He-Ne laser wavelength inside the spectrometer (such as 15770-15820cm -1 interval) can be truncated or deleted. Since this spectral test only involves the relative value of the response, there is no need to pay attention to the absolute value of the data, and the multiplication, division and normalization operations can be performed at any time to facilitate data processing.

Claims (1)

1. A broad-spectrum correction method for FTIR measurements of photodetector responses. The wide-spectrum correction method is based on the pyroelectric detector with a wide spectral range and flat response as the standard configuration of the FTIR spectrometer, and obtains the background spectrum required to correct the detector response spectrum through actual measurement and fitting calculations, and then Utilize this background spectrum to obtain the actual response spectrum of the photodetector to be measured; It is characterized in that described calibration method comprises the following steps: 1) By measuring the response of the pyroelectric detector and amplifier circuit to the combination of the selected light source and beam splitter at different scanning speeds, and then extracting relevant data to fit the analytical frequency response characteristics of the detector and amplifier circuit; 2) Correct the original output characteristics of the specific light source and beam splitter combination according to the analytical frequency response characteristics of the pyroelectric detector and the amplifier circuit obtained in step 1), so as to obtain the FTIR spectrometer under this specific light source and beam splitter combination Actual output characteristics; 3) According to the actual output characteristics of the corrected spectrometer obtained in step 2) as the background spectrum, the original response spectrum of the measured photodetector is referred to to obtain the corrected actual response spectrum of the photodetector.