阅读说明：本技术 相位差控制装置 (Phase difference control device ) 是由 三好有一 于 2019-01-30 设计创作，主要内容包括：本发明涉及一种能够在CD光谱仪中利用的相位差控制装置的响应性改善技术。相位差控制装置具备：分割偏振器(14),其将来自光源(12)的光分割成直线偏振的测定光和直线偏振的参照光；PEM(16),其以与分光测定相对应的方式对测定光和参照光赋予相位差；PEM驱动器(18),其向PEM(16)供给调制电压；PEM控制电路(24),其输入参照光作为反馈信号,并且向PEM驱动器(18)输出调制控制量信号,相位差控制装置还具备CPU电路(26),该CPU电路监视分割偏振器(14)的光的波长,并输入波长变化作为波长信号,CPU电路(26)将波长信号变换成前馈信号,前馈信号被输出到PEM控制电路(24),PEM控制电路(24)进行基于反馈信号和前馈信号的运算处理,来向PEM驱动器(18)输出调制控制量信号。(The present invention relates to a technique for improving the responsiveness of a phase difference control device that can be used in a CD spectrometer. The phase difference control device is provided with: a splitting polarizer (14) that splits light from the light source (12) into linearly polarized measurement light and linearly polarized reference light; a PEM (16) for giving a phase difference to the measurement light and the reference light so as to correspond to the spectroscopic measurement; a PEM driver (18) that supplies a modulated voltage to the PEM (16); and a PEM control circuit (24) that receives the reference light as a feedback signal and outputs a modulation control amount signal to the PEM driver (18), wherein the phase difference control device further comprises a CPU circuit (26) that monitors the wavelength of the light split into the polarizers (14) and receives a wavelength change as a wavelength signal, wherein the CPU circuit (26) converts the wavelength signal into a feedforward signal, and the feedforward signal is output to the PEM control circuit (24), and wherein the PEM control circuit (24) performs an arithmetic process based on the feedback signal and the feedforward signal and outputs the modulation control amount signal to the PEM driver (18).)

1. A phase difference control device used in a spectrometer for performing a spectroscopic measurement of a sample, the phase difference control device being characterized in that,

the phase difference control device includes: splitting the polarizer: which splits incident light from a light source into linearly polarized measurement light and linearly polarized reference light; a photoelastic modulator, that is, a PEM, that performs a phase modulation operation for imparting a phase difference to the measurement light and the reference light so as to correspond to the spectroscopic measurement; a PEM driver which supplies a modulation voltage for performing a phase modulation operation to the PEM; and a PEM control circuit which inputs the reference light as a feedback signal and outputs a modulation control amount signal to the PEM driver,

the phase difference control device further includes a CPU circuit for monitoring the wavelength of the light in the divided polarizer, inputting a change in the wavelength as a wavelength signal,

the CPU circuitry converts the wavelength signal into a feed forward signal, which is output to the PEM control circuitry,

the PEM control circuit performs an arithmetic process based on the feedback signal and the feedforward signal to output a modulation control amount signal to the PEM driver.

2. The phase difference control device according to claim 1,

the CPU circuit calculates a feedforward signal from an output instruction table previously created in the CPU circuit.

3. The phase difference control device according to claim 1 or 2,

the phase difference control device further comprises a temperature compensation circuit for supplying a modulation voltage for making a phase difference given to the measurement light and the reference light constant even if the temperature of the PEM changes from the PEM driver to the PEM,

the temperature compensation circuit receives a detection value detected by a temperature detector for detecting the temperature of the PEM and performs a temperature compensation operation.

4. The phase difference control device according to claim 3,

the PEM driver is configured to include the temperature compensation circuit in at least a portion thereof, the temperature compensation circuit configured to include a temperature compensated crystal oscillator.

5. A phase difference control method for controlling a phase difference of a PEM in a spectrometer including at least a light source, a splitting polarizer, a photoelastic modulator (PEM), a PEM driver, and a PEM control circuit, the phase difference control method comprising the steps of:

supplying a modulation voltage for performing a phase modulation operation from the PEM driver to a PEM, splitting incident light from a light source into linearly polarized measurement light and linearly polarized reference light by the splitting polarizer, imparting a phase difference to the obtained measurement light and reference light by the PEM in a manner corresponding to spectroscopic measurement, inputting the reference light to which the phase difference is imparted to the PEM control circuit as a feedback signal, and outputting a modulation control amount signal to the PEM driver to constitute a feedback control loop; and

the spectrometer is provided with a CPU circuit for monitoring the wavelength of light in the split polarizer and inputting the change in the wavelength as a wavelength signal, the CPU circuit converts the wavelength signal into a feedforward signal and outputs the feedforward signal to the PEM control circuit,

wherein the PEM control circuit outputs a modulation control quantity signal to the PEM driver using the feedback signal and the feedforward signal.

Technical Field

The present invention relates to a technique for improving the responsiveness of a phase difference control device used in various spectrometers and the like including a photoelastic modulator (PEM), and particularly a phase difference control device that can be used in a circular dichroism spectrometer (CD) and a linear dichroism spectrometer (LD).

Background

In the past, Photoelastic modulators (PEM) were used in various spectrometric measurements. Generally, a PEM is known as an element for phase modulating incident polarized light using birefringence. Moreover, the sensitivity of the polarized light measurement using the PEM is very high, and for example, when the wavelength of incident light to the PEM is changed, the phase modulation action of the PEM is also greatly influenced. That is, there is a possibility that the measurement result of the spectroscopic measurement is greatly affected by a change in the wavelength of incident light to the PEM or the like.

Therefore, patent document 1 discloses one of the following techniques: the phase difference control device is provided with a photoelastic modulator control circuit, and controls the ratio of the amplitude of the alternating current component having an angular frequency of 2 ω to the magnitude of the direct current component in the detected reference beam to be constant, so that the phase difference given by the photoelastic modulator can be kept constant even if the wavelength of light incident on the photoelastic modulator or the temperature of the photoelastic modulator changes.

Disclosure of Invention

Problems to be solved by the invention

However, by using the configuration of patent document 1 in the phase difference control device, it is possible to cope with an environmental change of the photoelastic modulator (a change in wavelength of incident light, etc.), but since this configuration has a limit in responsiveness of control (since it is control of acquiring whether or not a change is made in the photoelastic modulator as a signal, it is inevitably affected by the change), it is possible to cope with only step scanning when actually acquiring the spectrum data. That is, there are the following problems: such a technique cannot be applied to a spectrometer or the like that requires continuous scanning, such as a circular dichroism spectrometer.

Means for solving the problems

The present invention has been made in view of the above-described problems of the prior art, and an object of the present invention is to provide a phase difference control device and method that can achieve stable phase difference control even when a wavelength change of incident light or the like occurs in a photoelastic modulator, improve the responsiveness of phase difference control, and can also cope with continuous scanning.

In order to solve the above-mentioned problems, a phase difference control device according to the present invention is used in a spectroscopic measuring apparatus for performing spectroscopic measurement on a sample, the phase difference control device being characterized in that,

the phase difference control device includes: splitting the polarizer: which splits incident light from a light source into linearly polarized measurement light and linearly polarized reference light; a PEM that performs a phase modulation operation for applying a phase difference to the measurement light and the reference light so as to correspond to the spectroscopic measurement; a PEM driver which supplies a modulation voltage for performing a phase modulation operation to the PEM; and a PEM control circuit which inputs the reference light as a feedback signal and outputs a modulation control amount signal to the PEM driver,

the phase difference control device further includes a CPU circuit for monitoring the wavelength of the light in the divided polarizer, inputting a change in the wavelength as a wavelength signal,

the CPU circuitry converts the wavelength signal into a feed forward signal, which is output to the PEM control circuitry,

the PEM control circuit performs an arithmetic process based on the feedback signal and the feedforward signal to output a modulation control amount signal to the PEM driver.

In addition, the phase difference control device according to the present invention is characterized in that,

the CPU circuit calculates a feedforward signal from an output instruction table previously created in the CPU circuit.

In addition, the phase difference control device according to the present invention is characterized in that,

the phase difference control device further comprises a temperature compensation circuit for supplying a modulation voltage for making a phase difference given to the measurement light and the reference light constant even if the temperature of the PEM changes from the PEM driver to the PEM,

the temperature compensation circuit receives a detection value detected by a temperature detector for detecting the temperature of the PEM and performs a temperature compensation operation.

In addition, the phase difference control device according to the present invention is characterized in that,

the PEM driver is configured to include the temperature compensation circuit in at least a portion thereof, the temperature compensation circuit configured to include a temperature compensated crystal oscillator.

A phase difference control method according to the present invention is a phase difference control method for controlling a phase difference of a PEM in a spectrometer including at least a light source, a split polarizer, the PEM, a PEM driver, and a PEM control circuit, the phase difference control method including the steps of:

supplying a modulation voltage for performing a phase modulation operation from the PEM driver to a PEM, splitting incident light from a light source into linearly polarized measurement light and linearly polarized reference light by the splitting polarizer, imparting a phase difference to the obtained measurement light and reference light by the PEM in a manner corresponding to spectroscopic measurement, inputting the reference light to which the phase difference is imparted to the PEM control circuit as a feedback signal, and outputting a modulation control amount signal to the PEM driver to constitute a feedback control loop; and

the spectrometer is provided with a CPU circuit for monitoring the wavelength of light in the split polarizer and inputting the change in the wavelength as a wavelength signal, the CPU circuit converts the wavelength signal into a feedforward signal and outputs the feedforward signal to the PEM control circuit,

wherein the PEM control circuit outputs a modulation control quantity signal to the PEM driver using the feedback signal and the feedforward signal.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, the phase difference control device includes a PEM control circuit to form a feedback control loop, and further includes a CPU circuit to monitor a wavelength change of incident light to the PEM (a wavelength change of light in the split polarizer), to calculate a feed forward signal under a constant condition, and to calculate a modulation control amount signal by performing arithmetic processing on the feed forward signal and the feedback signal in the PEM control circuit. By controlling the PEM driver with the modulation control amount signal, the response is improved compared to the conventional one, and stable phase difference control can be achieved even when a wavelength change of incident light occurs. As a result, since the responsiveness of the phase difference control is improved, it is possible to realize, for example, a phase difference control device and method that can cope with not only step scanning but also continuous scanning.

Drawings

Fig. 1 is a schematic configuration diagram showing a CD spectrometer to which a phase difference control device according to an embodiment of the present invention is applied.

Fig. 2 is a schematic configuration diagram showing a modification of the CD spectrometer to which the phase difference control device of the present invention is applied.

Fig. 3 (a) shows a series TCXO circuit that can be used for a temperature compensation circuit in the present embodiment, and fig. 3 (b) shows an indirect TCXO circuit that can be used for a temperature compensation circuit in the present embodiment.

Description of the reference numerals

10: CD spectrometer (phase difference control device); 12: a light source; 14: dividing the polarizer; 16: a PEM; 18: a PEM driver; 20: a sample; 22: a detection circuit; 24: a PEM control circuit; 26: a CPU circuit; 28: a PMT detector; 30: a preamplifier; 32: a DC amplifier; 34: an operational amplifier; 36: adjusting the sensitivity HT; 38: a sense amplifier; 40: a lock-in amplifier; 42: a temperature compensation circuit; 44: a temperature detector.

Detailed Description

The phase difference control device of the present invention will be described below with reference to the drawings, but the present invention is not limited to the following examples as long as the gist of the present invention is not exceeded.

Fig. 1 is a schematic configuration diagram of a circular dichroism spectrometer (CD spectrometer) as a spectroscopic measuring instrument according to an embodiment of the present invention. The CD spectrometer 10 in fig. 1 is configured by applying the phase difference control device of the present invention. The CD spectrometer 10 shown in the figure includes: a light source 12 that irradiates light to the sample 20; a splitting polarizer 14 that splits the light from the light source 12 into monochromatic light and splits the incident light into polarized light of measurement light and polarized light of reference light (linearly polarized light); a PEM16 that performs a phase modulation operation for imparting a phase difference to the linearly polarized light from the splitting polarizer 14; a PEM driver 18 which supplies a modulation voltage for performing a phase modulation operation of the PEM 16; and a detection circuit 22 for detecting the measurement light transmitted through the sample 20. The CD spectrometer 10 of the present embodiment further includes a PEM control circuit 24 and a CPU circuit 26 for constituting the phase difference control device of the present invention.

Light from the light source 12 is split into monochromatic light by the splitting polarizer 14, and the monochromatic light is further split into measurement light obtained by linearly polarizing the monochromatic light and reference light obtained by linearly polarizing the measurement light in the same manner. The split polarizer 14 in the present embodiment is configured to include a monochromator, a Rochon (Rochon) prism, and the like. In the present embodiment, a monochromator for linearly polarizing the light from the light source 12 and a rochon prism for splitting the linearly polarized light may be separately configured. Any of the lights (measurement light and reference light) linearly polarized by the split polarizer 14 reaches the PEM 16. At this time, a modulation voltage is supplied from the PEM driver 18 to the PEM16, and when the measurement light and the reference light transmit through the PEM16, predetermined phase differences according to various measurements are given, so that the measurement light and the reference light become circularly polarized light alternating between left and right. Then, the measurement light of the left and right circularly polarized lights enters the sample 20.

The sample 20 is a measurement target having CD (circular dichroism), and when left and right circularly polarized lights (measurement lights) are transmitted through the sample 20, the left and right circularly polarized lights are absorbed in different amounts on the left and right sides, and are detected by the detection circuit 22 as lights including intensity variations depending on CD. The detection circuit 22 performs a predetermined process using various amplifiers and the like to output the CD value as a measurement result, and thereafter performs a spectrum analysis or the like using, for example, a spectrum analyzer or a personal computer.

Here, a description will be given of a detection process of the CD value in the detection circuit 22. The detection circuit 22 is composed of a PMT detector 28, a sensitivity adjustment HT 36, a lock-in amplifier 40, and a plurality of various amplifiers (a preamplifier 30, a DC amplifier 32, an operational amplifier 34, and a detection amplifier 38). The measurement light transmitted through the sample 20 is converted into a CD voltage by the PMT detector 28, and the voltage value of the CD voltage is amplified by the preamplifier 30. The CD voltage is amplified by various amplifiers inside the detection circuit 22 because it is a very weak voltage signal.

The CD voltage includes a direct current component and an alternating current component, and the direct current component in the amplified CD voltage is selectively amplified by the DC amplifier 32. The difference between the amplified CD voltage (dc component) and, for example, 1V is amplified at a predetermined ratio by the operational amplifier 34 and input to the sensitivity adjustment HT 36, and the sensitivity adjustment HT 36 adjusts the sensitivity of the PMT detector 28 so that the magnitude (voltage) of the dc component is constant.

Also, the CD voltage stabilized by these processes is input to the lock-in amplifier 40 via the sense amplifier 38. A reference voltage is input from the PEM driver 18 to the lock-in amplifier 40, and the CD value detected by the lock-in amplifier 40 is subjected to spectrum analysis for a predetermined purpose. The CD spectrometer 10 in the present embodiment detects a CD value roughly by the above procedure.

AboutPhase difference control

Next, the phase difference control of the PEM16 in the CD spectrometer 10 according to the embodiment of the present invention will be described. The CD spectrometer 10 includes a PEM control circuit 24 for realizing stable phase difference control, and the PEM control circuit 24 inputs the reference light in the PEM16 as a feedback signal (FB signal in fig. 1), and calculates a modulation control amount signal by performing arithmetic processing in the PEM control circuit 24 according to predetermined conditions.

Although not shown in fig. 1, the reference light input to the PEM control circuit 24 is converted into a voltage signal by, for example, a photomultiplier tube, and is input to the PEM control circuit 24 as a feedback signal. Further, the PEM control circuit 24 outputs a modulated control quantity signal to the PEM driver 18, and the PEM driver 18 supplies a modulated voltage corresponding to the modulated control quantity signal to the PEM16, thereby constituting a feedback control loop.

In this way, by performing the phase difference control of the PEM16 using the feedback control loop constituted by the PEM driver 18 and the PEM control circuit 24, even if the actual phase modulation amount deviates from the target phase modulation amount due to, for example, a wavelength change of the incident light in the PEM16 (such as a case where the wavelength is changed every measurement), a modulation voltage corresponding to the deviation of the phase modulation amount can be supplied from the PEM driver 18 to the PEM 16. As a result, even if the wavelength of the incident light to the PEM16 changes, stable phase difference control can be achieved by the feedback control loop.

The CD spectrometer 10 according to the present embodiment further includes a CPU circuit 26, and thus the CPU circuit 26 constitutes a phase difference control device together with the feedback control loop (the PEM16, the PEM driver 18, and the PEM control circuit 24). The CPU circuit 26 is configured to include a CPU (central processing unit) and the like, for example. The CPU circuit 26 in the present embodiment constantly monitors (monitors) the wavelength of light in the divided polarizer 14.

That is, the CPU circuit 26 constantly monitors the wavelength of light in the split polarizer 14 (the wavelength of incident light incident to the PEM 16), and receives the wavelength change as a wavelength signal. The wavelength signal input to the CPU circuit 26 is converted into a feedforward signal by being subjected to arithmetic processing by a table prepared in advance in the CPU circuit 26 or a predetermined algorithm, and then the feedforward signal (FF signal in fig. 1) is output to the PEM control circuit 24.

A feedback signal as reference light in the PEM16 and a feed forward signal calculated from a change in the wavelength of incident light incident to the PEM16 are input to the PEM control circuit 24. The PEM control circuit 24 calculates a modulation control amount signal by performing arithmetic processing on the feedback signal and the feed-forward signal, and outputs the modulation control amount signal to the PEM driver 18.

Calculation of feed forward signal

As described above, the feedforward signal is calculated by using a table prepared in advance or performing arithmetic processing based on an algorithm with respect to the wavelength signal (the wavelength change of the incident light to the PEM 16). For example, the feedforward signal can be calculated inside the CPU circuit 26 by using an output command table showing output commands corresponding to respective wavelengths. In this case, since there is a possibility that the characteristics of each PEM used in the spectroscopic measurement are slightly different, it is also possible to prepare different output instruction tables for each PEM.

Then, an output command table necessary for the spectroscopic measurement (phase difference control) can be obtained by calculating in advance a voltage value that becomes the maximum value of the CD. As a method of calculating the voltage value that becomes the CD maximum value, for example, the PEM voltage is increased at every designated step, CD value data corresponding to each PEM voltage is acquired, the peak position of the data is set to the CD maximum value, and the voltage value at that time is set to the vmax value.

The feedforward signal can also be calculated by a predetermined algorithm prepared in advance in the CPU circuit 26. For example, the PEM voltage is increased, decreased if the difference in CD values (differential value) becomes negative, and then increased if the differential value becomes negative. The convergence point at which this process is repeated can be set to the CD maximum value, and the voltage value at this time can be set to the vmax value.

As still another method, the feedforward signal can be calculated by executing a program including an optimization algorithm such as a steepest descent method or peak detection. Here, the steepest descent method is an algorithm of a gradient method in which the minimum value of a certain function is searched only from the slope (first order differential) of the function, or an algorithm based on a similar consideration method. In the present embodiment, the output command table can be created by the steepest descent method or peak detection. Further, although the output command table for each PEM can be obtained by calculating the vmax value obtained by the above-described method over the entire wavelength range and all wavelength points of the measurement device, the operation of calculating the output command table can be made efficient by limiting the wavelength at which the vmax value is calculated and performing interpolation using the following numerical expression showing the relationship between V and wavelength.

[ numerical formula 1]

λ: wavelength of light

Vm: maximum value of voltage

A: phase difference

Q: coefficient of photoelasticity

In addition, as the calculation of the feedforward signal, in a CD spectrometer or the like, a in the above numerical expression is 1.841 radians, but in an ellipsometer, for example, a in the above numerical expression is 2.405 radians, and the maximum value of the CD value can be calculated. Similarly, for example, in an optical rotation spectrometer (ORD) or a linear dichroism spectrometer (LD), the maximum value of the CD value can be calculated by setting a in the above numerical expression to 3.05 radians. The calculation algorithm of the feedforward signal in the CPU circuit 26 according to the present embodiment is not limited to the algorithm based on the above-described expressions and methods, and may be other algorithms and methods if the maximum value of the CD value can be calculated.

Specifically, the algorithm for calculating the CD maximum value in the output command table can be, for example, a gauss-newton method, a Pattern Search (Pattern Search) method, a Nelder-Mead method, a genetic algorithm, a particle swarm optimization, a differential evolution method, a cuckoo Search, a firefly algorithm, or the like.

As described above, by providing the CPU circuit 26 in addition to the feedback control loop to constitute the phase difference control device and performing the phase difference control by using the feedback signal and the feedforward signal, it is possible to perform the stable phase difference control even when the wavelength of the incident light is changed, and to realize the phase difference control having the response more excellent than the conventional one. As a result, by improving the responsiveness, it is possible to cope not only with step scanning but also with continuous scanning, and therefore, for example, the phase difference control device of the present invention can be used for a CD spectrometer, an LD spectrometer, or the like that requires continuous scanning.

< modification example >

In the PEM characteristics, the Q value is very high, and therefore, even if a slight temperature change occurs, the transmission frequency greatly fluctuates, and the measurement result may be greatly affected. Therefore, the phase difference control device in the present modification is configured by adding a circuit configuration capable of coping with the influence of such temperature change.

Fig. 2 is a schematic configuration diagram showing a modification example of the CD spectrometer according to the embodiment of the present invention. In fig. 2, as in fig. 1, the CD spectrometer 10 is configured by applying the phase difference control device of the present invention. The CD spectrometer 10 of fig. 2 has basically the same configuration as the CD spectrometer 10 shown in fig. 1, but in the present modification, a temperature compensation circuit 42 is provided to further improve the stability of the phase difference control in the PEM 16.

The temperature compensation circuit 42 is provided integral with the PEM driver 18, for example by being connected to the internal circuitry of the PEM driver 18. In the temperature compensation circuit 42, a temperature detector 44 such as a thermistor or another thermometer is disposed in the vicinity of the PEM16 (or disposed in contact with the PEM 16), and a temperature detection value (temperature detection signal) from the temperature detector 44 is input to the temperature compensation circuit 42, thereby realizing a temperature compensation operation in the phase difference control.

As the temperature compensation circuit 42, for example, a TCXO type (temperature compensation type crystal oscillator) circuit such as a direct TCXO shown in fig. 3 (a) or an indirect TCXO shown in fig. 3 (b) can be used. The temperature compensation circuit 42 in the present modification is not limited to the TCXO type circuit configuration, and other circuits may be used as long as the temperature compensation operation of the PEM16 can be realized.

In the phase difference control, the ambient temperature of the PEM16 (or the temperature of the PEM16 itself) detected by the temperature detector 44 is input as a temperature detection signal to the temperature compensation circuit 42. When the temperature detection signal is input, the resistance value of the temperature compensation circuit 42 changes in accordance with the detection value, so that the PEM driver 18 can supply an appropriate modulation voltage corresponding to the temperature change of the PEM 16.

That is, in the present modification, the PEM control circuit 24 performs the phase difference control of the PEM16 using the feedback signal and the feedforward signal, and at the same time, detects the temperature of the PEM16 and performs the control by the temperature compensation circuit 42, thereby achieving stable phase difference control that is more responsive than in the past and suppresses the influence of the temperature change of the PEM (and the periphery of the PEM).

Further, according to the present invention, the following steps are performed as described above: a step of inputting a feedback signal from the PEM16 by the PEM control circuit 24 and outputting a modulation control amount signal to the PEM driver 18, thereby constituting a feedback control loop; and a step of outputting a feedforward signal obtained based on the wavelength change of the light in the split polarizer 14 monitored by the CPU circuit 26 to the PEM control circuit 24, and the PEM control circuit 24 performs a predetermined arithmetic process using the feedback signal and the feedforward signal to output the modulation control amount signal to the PEM driver 18, thereby making it possible to realize a phase difference control method capable of performing stable phase difference control having more excellent responsiveness than the conventional method and less influence of the wavelength change of the incident light to the PEM 16.

In the above-described embodiment and modification, the phase difference control device and the phase difference control method according to the present invention are applied to a CD spectrometer, but the same effects can be obtained when the phase difference control device and the phase difference control method are applied to other spectrometers such as an ellipsometer, an optical rotation spectrometer (ORD), and a linear dichroism spectrometer (LD).