JPS5858444A - Laser raman spectroscopical method and device for elimination of fluorescence - Google Patents

Abstract

PURPOSE:To measure a Raman spectrum with a high S/N, by irradiating a sample with the laser for exciting the Raman scattered light and the laser for exciting the fluorescence of a prescribed intensity alternately in the same duration and subjecting detection values of excited lights to the subtraction processing. CONSTITUTION:A sample 9 is irradiated with two kinds of laser light from a laser 1 for exciting the Raman scattered light and a laser 2 for exciting the fluorescence, which has the intensity adjusted so that the fluorescence having the same intensity as the fluorescence in the Raman scattered light excited by the laser light of the laser 1 is excited, alternately through an optical chopper 3 in the same duration. Photoelectron pulses corresponding to the excited Raman light and the fluorescence from the sample 9 are detected by a spectrometer 11 and a detector 12 and are subjected to the subtraction processing in a photoelectron pulse adding/subtracting counter 14 to eliminate a fluorescence spectrum in the Raman spectrum. Noise components are eliminated simultaneously, and thus, the laser Raman spectroscopical measurement based on the Raman spectrum is performed with a high S/N.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a V-Zaraman spectroscopy method for eliminating interference with Raman scattering light measurement due to fluorescence, and a method for analyzing minute goi and foreign substances attached to iron@VC-related semiconductors, thin film products, etc. As a method, Luraman spectroscopy using a laser t-excitation light source is effective, but in addition to Luraman scattered light, strong fluorescent light may be generated by the sample. In particular, samples of industrial materials containing many impurities that have been subjected to medium heat abrasion generate fluorescence at a high rate. Such fluorescence is generally stronger than the 2-man scattered light and has a wider width, so that the back-scattered light is hidden, making analysis impossible if fluorescence occurs. However, it is not possible to extract only a small sample and perform operations such as purification. Therefore, it is necessary to provide the analyzer with a fluorescence removal function.

Conventionally, in order to remove fluorescent tubes that interfere with Raman scattered light measurements, time-resolved methods that take advantage of the lifetime of fluorescent light and methods that utilize the difference in polarization between fluorescent light and line scattered light have been used. ing. However, these methods have short fluorescent lifetimes of 1 picosecond! It is not a versatile method because it is not constant and the difference in polarization is not a generally valid physical property. - In addition, one continuous wave A laser is used to simultaneously oscillate multiple oscillations, and among these, 4 - 5145 beams are used to excite fluorescent light at 48ζa, and 514.5S is used for Raman scattering. By measuring the superimposed spectrum of light and fluorescence, 48ζ
A versatile method of subtracting the QSIK-excited fluorescence spectrum has been used. In this method, 48a,
Ωm++a Semicircular filters that pass through each button screen are attached to the workpiece 51 to form a disk shape, and rotation is applied to this disk filter.

A large number of laser beams are oscillated simultaneously through a rotating disc filter, and 48ζG% light, 51ζ, and %n@ light are alternately extracted and irradiated onto the sample, which is excited by 514.5S Rin and generated. The Stokes Raman scattered light is dispersed by a field tube spectrometer and detected by a detector.

The output of the detector is 488. The output during thermal irradiation is divided into two parts, and after a frequency-voltage conversion cycle, the output of the recording needle is (+) fill, C-') i4.
are output, and the difference between each output is recorded. - This method takes advantage of the property that the optical wavelength of fluorescent light does not depend on the wave density of the incident light.
It is based on the fact that only fluorescence is concentrated in the Stokes Raman scattering region excited by 45ss (J, F, Mar
&@*gm, ApplimcL 0ptics, 15(
2), 2?49 (1974))*L However, in this method, 488. ＾514.
Because Ssm f is used, the laser light output cannot be adjusted independently, and the level of fluorescence during 48B, O arithmetic excitation is adjusted by reducing the output of the frequency-voltage converter with an attenuator. An improvement in the ratio cannot be expected, and if the fluorescence is strong, the fluorescence cannot be subtracted completely. Moreover,
Since a filter is used to select the laser beam, the intensity of the laser beam irradiated onto the sample is weak (4), the intensity of the generated Raman scattered light is weakened (4), and noise is increased.

In addition, as an improvement to the above-mentioned method, we used 21 laser light sources, independently changed the laser light output to 1III11, and changed the optical switch to obtain a fluorescence spectrum and a smooth spectrum in which line scattered light and fluorescence were superimposed. The fluorescence spectrum is excited periodically and alternately, and the fluorescence spectrum superimposed on the Raman scattered light is made stronger and stronger by adjusting the light output, and then the detector output direction is adjusted. By performing clock-in amplification at the optical switch switching frequency, it is possible to remove the interference Wt of fluorescent light, and also remove random noise that becomes 1 in the output signal, so that the S/7v ratio of Raman scattered light detection can be improved. However, for Raman, especially for most organic materials, its intensity is 1.
0 W7cya'' or less.The output waveform from this platform and photodetector is not a direct current but a photoelectron pulse train9.

14 Therefore, in a weak region where the Raman scattered light intensity is 10-8 or less, it is not possible to obtain a sufficiently large spectral signal using the lock-in amplification method, which is a direct current amplification method.

An object of the present invention is to eliminate the drawbacks of the prior art, eliminate fluorescent light that is an interference during measurement of Raman scattered light, and provide good S.
The object of the present invention is to provide a laser Raman spectroscopy method capable of measuring a Raman spectrum at an lN ratio, and a laser Raman spectroscopy system*1 capable of accurately carrying out the method.

The present invention is constructed as follows.

In other words, on the platform where the fluorescence power is superimposed on the Raman scattering spectrum and the fluorescence interferes with the Raman scattering light measurement, the fluorescence excitation laser that oscillates continuously and independently and the long-wavelength Raman scattering from the fluorescence excitation laser are used. 211 of optical excitation laser
Using 1 laser beam and changing the optical switch! 2ft
The laser beam 11118 is irradiated onto the sample periodically and alternately with the same time width. In the Stokes Raman spectrum region located at the long wavelength of the oscillation wavelength of the Raman scattering excitation laser, the fluorescence spectrum is measured when the sample is irradiated with the fluorescence excitation laser, and the Raman? Scattered light 10 When a sample is irradiated with a laser beam detector, the weight of the Raman scattering spectrum and fluorescence spectrum is measured. In addition to this, by adjusting the emission direction of the fluorescence excitation laser, the intensity of the fluorescence excited by the fluorescence excitation laser can be made equal to the intensity of the fluorescence superimposed on the Raman scattered light. Pigeon lofts that meet this condition, 9
When irradiated with the Raman scattering light excitation laser, the number of photoelectron pulses (NR) output from the detector is proportional to the intensity of the Raman scattering light.
The number of photoelectron pulses (N
F) and a number of photoelectron pulses (NN) proportional to the noise
When the fluorescence excitation laser is irradiated, the sum of the number of photoelectron pulses (Ar, ) proportional to the fluorescence intensity and the number of photoelectron pulses (NN) proportional to the noise is CNp + NN), so that the output pulses dispersed by the spectrometer and detected by the detector are added or subtracted in synchronization with the switching of the optical switch. (NR + NF + NN) - (NF + NN)
- Only Raman scattered light can be counted with NR. At this time, photoelectron pulses caused by Raman scattered light are digitally integrated,
Since there is no limit to the integration time, syH increases as the integration is repeated.
In particular, it becomes possible to detect Raman scattered light for a sample whose Raman scattered light is a weak light of 10"4 F/#- or less.

Hereinafter, the present invention will be explained based on the drawings. I will clarify.

FIG. 1 shows the basic configuration of the present invention, and FIG.
The photoelectronic pulse output from the detector that detects the scattered light, the pulse amplified by the preamplifier, and the voltage waveform manually input to the photoelectronic pulse adder by the optical chip.

As shown in the jlN1 diagram, the present invention is equipped with an Ir+ laser for Raman scattering pre-activation, +A laser for fluorescence excitation, and laser 2.

The oscillated laser beam for the pre-scattering activation 'r V-f I K is connected to the laser beam of the sublayer 55, and the laser beam for fluorescence excitation A2
Laser 2) continuously oscillates in -4,5? The passed 4Ba, Os+a laser beams are collected by an optical chisel placed on the optical path of these two types of laser beams, or by a pair of 7# condenser lenses, which are periodically and alternately assembled. Build-6. Harnra 7. It is configured to irradiate the sample 9 through 60 sets of condensing lenses.

The fluorescence Af laser 2 has a fluorescence intensity output a
mms <- (not shown) is built-in, and sales car 11
14 Keiko's 5 which was manned by K party excitation motion A + laser 2! The intensity of the fluorescent light obtained by superimposing the R degree on the Raman scattered light is impressive [! In addition, on the optical path of the light generated from the sample 9, there is a condenser lens 10 and a spectrometer 1
1 and a detection tIF 12 are arranged, and the sample! The light emitted from the unit enters the spectroscope 11 through the condenser lens 10,
It is dispersed by the iron spectrometer 11 and detected by the detector 12, and is transmitted from the cough detector 12 to the Raman scattered light excitation laser I.
When a sample is irradiated with K, a photoelectron pulse is output that is proportional to the intensity of fluorescent light and the fluorescence and noise multiplied by 1, and when a sample is irradiated with fluorescence excitation A laser 2, a photoelectron pulse is output that is proportional to the intensity of fluorescent light and noise. &C is configured so that pulses are output. Said fluorescence excitation A laser 2
The intensity of the Raman light, fluorescence, and noise generated during sample irradiation is shown by the reference numeral 11 in the figure. The photoelectron pulse t-1ifl is shown at 18 in FIG.

A preamplifier 15 is connected to the detector 12, and a counter 14 for adding and subtracting child pulses to the light coupled to the optical chip 5 is connected to the scissor device amplifier 11. The photoelectronic pulse output from the detector 12 is amplified by the preamplifier 1s, and the preamplifier output pulse is input to the photoelectronic pulse addition/subtraction counter 14 connected to the optical chip and detector system. be done. In addition, preamplifier 1
The amplified fluorescence and noise photoelectron pulses are shown in Figure 2 with the symbol 1? A photoelectronic pulse of Raman light and noise amplified by the same preamplifier 1i is shown in the diagram t-12 with reference numeral 2o.

In addition to the preamplifier output pulses, a rotational frequency reference signal 16 of the optical chipper 3 is also input to the photoelectronic pulse addition/subtraction counter 14, and the preamplifier output pulse is the reciprocal of the rotational frequency of the optical chipper 5. During the given opening and closing time,
Counted by a photoelectronic pulse addition/subtraction counter. That is,
When the sample 9 starts to be irradiated with the light of the rotating optical chip 1 for excitation of scattered light, the photoelectron pulse from the detector 12 is amplified by the preamplifier 1s, and the output of the preamplifier is The pulses are counted by the photoelectronic pulse addition/subtraction counter 14 until the +r laser 10 light is cut off by the optical chisel collar S for excitation of Raman scattered light.
will be added. Subsequently, when the sample 9 is irradiated with the light from the A+laser 2 for fluorescence excitation, a photoelectron pulse is generated in the same way as described above, and the output pulse from the preamplifier 11 is converted to A for fluorescence excitation by the photoelectron pulse addition/subtraction+counter 14. , Until the source of the laser 2 is cut off by the optical chip explosion, the total is 1, and the count value of the photoelectronic pulse intermittent counter 14 that was previously added is subtracted. The voltage waveform tube of the optical chip rotation frequency reference signal, which is inserted from the optical chip into the photoelectronic pulse addition/subtraction counter 14, is indicated by reference numeral 16 in FIG.

The photoelectronic pulse addition/subtraction counter 14 includes a recorder 15.
), and according to the rotation of the optical chipper 6,
The above-mentioned addition/subtraction cycle of the number of photoelectronic pulses is performed seven predetermined times, and the final count 11 is inserted into the recording needle ISK and recorded.

At this time, adjust the output of A for fluorescence excitation, + the output of laser 2, A for axillary fluorescence excitation, and the output X At this time, in order to match the level of the photoelectron pulse number t of fluorescence detected by the detector 12, the photoelectron pulse addition/subtraction counter 4 is injected with a Kr+ laser for excitation of scattered light on the sample 9.
The number of photoelectron pulses caused by the noise (NN) is added, and when the sample 9 is irradiated with the fluorescent excitation Ar+-the 2, the fluorescence (NN) is added.
Since the number of photoelectronic buses A caused by N ) + noise CN, ) is subtracted, only the beak scattered light from which the superimposed fluorescent light has been removed is obtained after the optical chip 5 rotates once. It will be done.

can.

Furthermore, the aforementioned engineering'! By repeating jAkk, photoelectron pulses are added fjk3i! The counter 4 integrates the Raman scattered light N-II and increases the s7y ratio of the Raman scattered light.

The present invention has the above-described configuration and operation, and according to the method of the present invention, 2I laser beams are periodically and alternately emitted toward the sample for the same period of time from a fluorescence excitation laser and a Raman scattering excitation laser. ↓
The fluorescence spectrum when the sample is irradiated by the Raman scattering light excitation laser, and the Raman scattering light spectrum and the fluorescence spectrum when the sample is irradiated by the Raman scattering light excitation laser are measured. and the intensity of fluorescence superimposed on the Raman scattered light, and then calculate the output signal generated when the sample is irradiated by the Raman scattered light excitation laser and the output signal generated when the sample is irradiated by the fluorescence excitation laser. Since the output signal is subtracted to obtain the signal of only the Raman scattered light and then integrated, it is possible to efficiently remove the fluorescent light superimposed on the weak Raman scattered light. At the same time, since noise can be reduced, it is possible to measure Raman scattering spectra with a good SIN ratio, which was difficult to measure in conventional measurements due to fluorescence interference.

Furthermore, according to the device of the present invention, the fluorescence intensity tiill
l! Two ellipsoidal laser beams are continuously oscillated toward the sample from a laser for excitation of fluorescent light and a laser for excitation of Raman scattering light, and the two laser beams are periodically and alternately applied to the sample to the acousto-optical switch. The 2@ laser beams are irradiated with the same time width, and the laser beam is focused on the sample using the condensing optical system. Light, Raman scattered light is dispersed, the dispersed light is detected by a detector and converted into an output signal, and the output signal from the detector and the switching frequency and total addition/subtraction pulse from the optical chisel filter are detected. The 111c pulse counter calculates the intensity of the fluorescence excitation laser from the output signal proportional to the intensity of the Raman scattering light generated when the sample is irradiated with the Ephraman scattering excitation laser, the fluorescent light charged thereto, and the noise. The total output signal 1jf1. is proportional to the intensity of fluorescence and noise generated during sample irradiation. Raman scattered light component only)j
Since i; L is calculated and t is integrated, the method described above can be carried out reliably and appropriately.

[Brief explanation of the drawing]

11th Cane A block diagram showing an embodiment of the apparatus for carrying out the method of the present invention, FIG. 2 shows the photoelectronic pulse, which is the output signal output from the detector, the pulse amplified by the preamplifier, and the rotation of the optical chifura tube. 8 is an explanatory diagram showing the voltage waveform of the number reference signal. FIG. 1...K laser for Raman scattering light excitation, 2...A laser for fluorescence excitation, 3...Optical server, 45.6
．． 7-...Mirror, 8...Condenser lens,! ...Sample, 10...Condensing lens, IL-spectroscope, 12...
Detector, 1S... Preamplifier, 14-... Photoelectronic pulse addition/subtraction counter, 15... Recording needle, 16... Optical chip flange rotation frequency reference signal, 17... Laser sample for fluorescence excitation Photoelectronic pulse i18 of fluorescence and noise generated during irradiation...Photoelectronic pulse of Raman scattered light generated when irradiating a sample with the laser for excitation of Raman scattered light, fluorescence and noise multiplied by this, 19.20... Pulses amplified by a preamplifier. Representative Patent Attorney Bo 1) Li: Shin, - 1st Mountain

Claims (1)

[Claims] 1. A sample is periodically and alternately irradiated with two types of laser light from a fluorescence excitation laser and a Raman scattered light excitation laser having a longer wavelength than the fluorescence excitation laser with the same time width. , the fluorescence spectrum when the sample is irradiated by the fluorescence excitation laser and the superimposed spectrum of the Raman scattered light spectrum and the fluorescence spectrum when the sample is irradiated by the Raman scattering excitation laser are measured, and The IMM is arranged so that the intensity of the fluorescent light superimposed on the Raman scattered light is relatively equal to the intensity of the fluorescent light superimposed on the Raman scattered light, and the Raman scattered light generated when the sample is irradiated by the Raman scattered light excitation laser and the fluorescent light superimposed on the Raman scattered light are It converts light and noise into an output signal proportional to their intensity, and converts the fluorescence and noise generated when a sample is irradiated by a fluorescence excitation laser into an output signal proportional to its intensity. A laser Raman spectroscopy method for removing fluorescence characterized by subtracting an output signal generated during irradiation and an output signal generated during irradiation of a sample with a fluorescence excitation laser, counting signals of only Raman scattered light, and calculating St. . 2. A fluorescence excitation laser that continuously oscillates fluorescence and can adjust the fluorescence intensity t for irradiating the sample, and a Raman scattering excitation laser that continuously oscillates a long-wavelength light tube like the fluorescence excitation laser. and on the optical path of these laser beams, an optical switch for periodically and alternately irradiating the sample with the two types of laser beams with the same time width, and a concentrator for irradiating the sample with the laser beams. A light optical system is provided on the optical path of the fluorescent light and Raman scattered light generated from the sample, and a condensing optical system for introducing these two lights into the spectrometer, and a condensing optical system for dispersing the fluorescent light and Raman scattered light. and a detector for detecting dispersed fluorescence, Raman scattering, and scattered light. and manually,
Among the detector output signals, an output signal proportional to the intensity of Raman scattered light generated in synchronization with Raman scattered light excitation laser irradiation, fluorescence and noise superimposed thereon is generated in synchronization with fluorescence excitation laser irradiation. Fluorescence is removed by connecting a photoelectronic needle counting device 1 that subtracts an output signal proportional to the stiffness of fluorescence and noise in the same addition/subtraction pulse counter to extract and reduce only the Raman scattered light component. Laser Raman spectrometer.