CN112666137A - LIF measurement fluorescence signal narrow-band filtering system and method based on FP interferometer - Google Patents
LIF measurement fluorescence signal narrow-band filtering system and method based on FP interferometer Download PDFInfo
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Abstract
The invention discloses a narrow-band filtering system and method for measuring a fluorescent signal by LIF (laser induced fluorescence) based on an FP (Fabry-Perot) interferometer, which comprises a laser source, wherein the emitted laser signal enters a laser modulator, is modulated by the laser modulator and then emitted to target particles, and is collected by an optical lens group, the optical lens group is connected to the FP interferometer, the FP interferometer is connected with a sensor, and then the signal of the sensor is output to a first phase-locked amplifier, and the reference signal of the first phase-locked amplifier is from a modulation reference signal output by the laser modulator; and the second phase amplifier is used for signal acquisition, the FP interferometer is subjected to scanning modulation of resonance frequency, the modulation signal of the FP interferometer is used as a reference signal, secondary phase-lock amplification is carried out on the LIF fluorescence signal which is output by the first phase-lock amplifier and subjected to phase-lock amplification, and narrow-band filtering with the bandwidth of 0.1-0.5nm is realized by using the fineness of the FP interferometer.
Description
Technical Field
The invention relates to the field of active spectral measurement, in particular to a narrow-band filtering system based on an FP interferometer and suitable for LIF fluorescence signal measurement.
Background
LIF (laser induced fluorescence) is an active optical diagnosis method with extremely high sensitivity and mature development, and has the characteristics of large excitation section, high space-time resolution and the like. LIF, TALIF, LCIF, LIQ and other measuring methods using laser-induced fluorescence as a basic principle are widely applied to experimental physics research such as hydrodynamics, plasma physics, molecular dynamics, quantum mechanics, combustion and the like. LIF, TALIF, LCIF, LIQ and other measurements using laser-induced fluorescence as a basic principle are mainly applied to diagnosis of kinetic parameters such as ion velocity distribution function and the like in plasma diagnosis; measuring the movement and distribution of substances capable of generating fluorescence by excitation in molecular dynamics and hydromechanics; the ultra-fine structure of atomic molecular spectrum can be measured in quantum mechanics; measurements of the concentration, distribution, etc. of the particles of interest may be made in combustion studies.
The most basic principle of LIF, TALIF, LCIF, LIQ and other measurement methods using laser-induced fluorescence as a principle is that a three-level system is utilized, incident narrow-band single-frequency laser is utilized to pump particles in a ground state or a metastable state to an excited state, the service life of the excited state is generally short (about a few nanoseconds), electrons on the excited level rapidly and spontaneously transition to the ground state or other levels, and fluorescence photons are released. According to different relationships among three energy levels and excitation mechanisms, laser-induced fluorescence types can be divided into five types: resonance fluorescence, off-resonance Stokes fluorescence, off-resonance anti-Stokes fluorescence, collision-assisted off-resonance Stokes fluorescence, and collision-assisted dual-resonance fluorescence. In physical experiments focusing on particle velocity measurement, such as fluid mechanics, plasma physics, molecular dynamics and the like, the Doppler effect can be utilized, a tunable laser with a scannable wavelength is used, corresponding fluorescence intensity changes under different wavelengths are measured through wavelength scanning of the laser, and velocity distribution of projection of ground state or metastable state particles in the incident laser direction can be obtained through calculation by bringing the Doppler effect into. The basic assumption of LIF, TALIF, LCIF, LIQ, and other measurement methods using laser-induced fluorescence as a principle is that the ground state or metastable particle temperature coincides with the host particle ground state temperature, and therefore parameters such as a velocity distribution function of the particles can be obtained by correlation measurement. In fluid mechanics, combustion and molecular dynamics research, the method can also be applied to measurement of density, spatial distribution and the like of target particles, and at the moment, a fixed-wavelength laser can be adopted to pump the target particles and collect the intensity and distribution of fluorescence signals on the space, so that the density, spatial distribution and the like of the target particles can be obtained. The laser-induced fluorescence can be applied to the measurement of the atomic hyperfine structure in quantum mechanics.
Fluorescence signals of LIF, TALIF, LCIF, LIQ and other measuring methods using laser-induced fluorescence as a principle have isotropic characteristics, and the fluorescence signals of an observation area are imaged on a sensor through a certain lens combination in a collection light path to receive the fluorescence signals. Background light with other wavelengths in the plasma has great influence on the signal-to-noise ratio of the fluorescence signal, and the signal-to-noise ratio can be improved by increasing the receiving angle of the fluorescence signal, the difference of the background light signal, laser modulation phase-locked amplification, average acquisition and other modes. A narrow-band filter with the wavelength corresponding to the fluorescent signal is added in front of the sensor, so that the signal-to-noise ratio can be well improved. The ideal fluorescence collection needs a narrow-band filter with at least 3-5nm bandwidth and at most 0.1-0.5nm bandwidth, which puts high requirements on the production and research and development capabilities of the related optical industry, and at present, the production and research and development capabilities of related high-performance products are still not available in China.
Disclosure of Invention
In the measurement process of LIF, TALIF, LCIF, LIQ and other measurement methods using laser-induced fluorescence as a principle, the improvement of the signal-to-noise ratio of a fluorescence signal is one of the most important problems. In the laser-induced fluorescence-related research of plasma physics, combustion and the like, excited-state ions which spontaneously transit to generate fluorescence photons have two main sources, namely fluorescence generated by laser pumping and fluorescence generated by electron collision excitation or background light generated by other light-emitting mechanisms. For fluorescence signals required to be collected by LIF, TALIF, LCIF, LIQ and other measurement methods using laser-induced fluorescence as a principle, the interference of fluorescence or background light generated by excited-state ions generated by electron collision excitation can affect the measurement accuracy of diagnosis. In addition, for the physical research of plasma, especially for hot cathode discharge plasma, the LIF fluorescence signal is seriously affected by the background light such as spontaneous transition fluorescence photons of ions in other excited states in the plasma and the luminescence of the hot cathode itself when the fluorescence signal is collected. Therefore, in the process of building a laser-induced fluorescence correlation diagnosis system, an amplitude modulator such as an EOM (equivalent-to-average modulation), an AOM (automatic optical modeling), a chopper and the like is often introduced to cooperate with a lock-in amplifier to carry out lock-in amplification on a fluorescence signal generated by a laser pump, and meanwhile, a high-performance narrow-band optical filter is added in a fluorescence signal receiving light path to improve the signal-to-noise ratio. Currently, excellent products with domestic and proprietary property rights such as amplitude regulators and phase-locked amplifiers (EOM), AOM, choppers and the like exist, but the production of domestic narrow-band filters with the bandwidth of 1-10nm still has difficulty, filters with the bandwidth of 0.5-1nm do not have the autonomous production and research and development capability at present at home, while LIF acquisition requires narrow-band filters with the bandwidth of 0.5-1nm, obviously, the capability of domestic products at present cannot meet the performance requirements, and a new solution is urgently needed to complete filtering.
In order to realize a narrow-band filtering system with a bandwidth of 0.1-0.5nm by using the existing domestic optical device, the invention considers that when a fluorescent signal is received during LIF measurement, background light can influence the signal-to-noise ratio of the fluorescent signal of the LIF in LIF, TALIF, LIQ and other measurement methods using laser-induced fluorescence as a principle, and the signal-to-noise ratio of the fluorescent signal can be effectively improved by using the high-performance narrow-band filtering optical system. The FP interferometer produces a high peak in its transmission spectrum when it satisfies the resonance condition for the incident light frequency. By utilizing the characteristic, the FP interferometer is widely applied to an incident light path of the LIF, a peak value is formed on a transmission spectrum of the FP interferometer by utilizing the periodic change of the wavelength during laser scanning, every time when the incident laser changes the fixed wavelength, the peak distance meets the free spectral region of the FP interferometer, and the laser wavelength can be calibrated during laser scanning by utilizing the known free spectral region of the FP interferometer and the characteristic peak of the known wavelength on an atomic absorption (emission) spectrum. The resonance frequency of the FP interferometer can be tuned by changing the incident light angle, the cavity length and the like, and the FP interferometer can generate a strong transmission spectrum for the incident light with a certain fixed wavelength by changing the resonance frequency of the FP interferometer, at the moment, the corresponding bandwidth of the FP interferometer to the incident light is determined by the fineness of the FP interferometer, and the fineness of the FP interferometer is determined by the reflectivity of a cavity reflector of the FP interferometer. By utilizing the characteristics, the FP interferometer can be used for narrow-band filtering with a specified bandwidth under a specified wavelength.
The technical scheme adopted by the invention is as follows: a narrow-band filtering system for measuring a fluorescent signal based on LIF of an FP interferometer comprises a laser source, wherein the emitted laser signal enters a laser modulator, is modulated by the laser modulator and then is emitted to target particles, the fluorescent signal is collected through an optical lens group, the optical lens group is connected to the FP interferometer, the FP interferometer is connected with a sensor, then the sensor signal is output to a first phase-locked amplifier, and a reference signal of the first phase-locked amplifier is from a modulation reference signal output by the laser modulator;
the FP interferometer can change the self resonant frequency through tuning, the lens group or the optical component is used for collimating and parallelly inputting the fluorescent signal into the FP interferometer, the resonant frequency of the FP interferometer is tuned to the position equivalent to the specified wavelength through the first phase-locked amplifier and the wavelength meter, so that the FP interferometer generates a transmission spectrum for the incident light with the specified wavelength, and the narrow-band filtering with the frequency width of 0.1-0.5nm is realized;
or the second phase amplifier is used for signal acquisition, the FP interferometer is scanned and modulated in resonance frequency, the modulation signal of the FP interferometer is used as a reference signal, the LIF fluorescence signal which is output by the first phase-locked amplifier and is subjected to phase-locked amplification for the second time, and narrow-band filtering with the bandwidth of 0.1-0.5nm is realized by using the fineness of the FP interferometer.
Furthermore, the optical lens group adopts a convex lens group to complete parallel collimation of a light path, so that the fluorescent signal of the LIF collection area is incident into the FP interferometer in parallel.
Further, the FP interferometer is provided with a rigid shell for fixing the FP interferometer, the stability of the resonance frequency of the FP interferometer during measurement is prevented from being influenced by the cavity length and the change of the incidence angle of the FP interferometer caused by installation, the relative positions of the FP interferometer, the lens group and the sensor are ensured to be fixed when the FP interferometer is used as a narrow-band filtering system, and the position of the whole receiving light path and the focal length of the lens group are changed when the receiving position is adjusted, so that the relative positions of the lens group, the FP interferometer and the sensor cannot be changed.
Further, the FP interferometer can change the cavity length through piezoelectric ceramic to perform resonance frequency tuning, or can change the cavity length of the FP interferometer through changing temperature to perform resonance frequency tuning, or can adjust the resonance frequency of the FP interferometer through adjusting the incident light angle, or can adjust the resonance of the FP interferometer through changing the refractive index of the light-transmitting medium.
Furthermore, the wavelength calibration of the resonance frequency of the FP interferometer is carried out by a lock-in amplifier method or a direct measuring method of a wavelength meter, the FP interferometer tuned to the resonance frequency consistent with the fluorescence wavelength is used for carrying out narrow-band filtering on the target wavelength and 0.1-0.5nm nearby the target wavelength, and the transmission spectrum of the FP interferometer is received by a sensor after the FP interferometer is interfered and is used for signal acquisition.
Further, when a second phase amplifier is used for signal acquisition, the oscilloscope is connected to a second phase-locked amplifier, and the second phase-locked amplifier is also connected to the first phase-locked amplifier and a modulation power supply of the FP interferometer respectively; the first phase-locked amplifier is connected to the FP interferometer sensor, and the reference signal of the first phase-locked amplifier is connected to the modulation reference signal output by the self-excitation light modulator.
Furthermore, the FP interferometer is rigidly connected with the lens group or the optical assembly and the sensor by a rigid shell of the FP interferometer, so that the cavity length and the incidence angle of the FP interferometer are not changed by the fixing mechanism II, and the relative position of the components is not changed during the measurement.
The invention also provides a LIF measurement fluorescence signal narrow-band filtering method based on the FP interferometer, and the system comprises the following steps:
LIF utilizes incident laser to actively excite target particles to an excited state, the target particles in the excited state can spontaneously jump to a low level to release photons to generate fluorescence signals, the incident laser is subjected to amplitude modulation through an acousto-optic modulator or electro-optic modulator modulation means, the modulation signals of the acousto-optic modulator or the electro-optic modulator are input into a first phase-locked amplifier to serve as reference signals, the first phase-locked amplifier of the reference signals is used for performing phase-locked amplification on the fluorescence signals received by a sensor, the phase-locked amplification and the reference signals have the same frequency and the same phase, and at the moment, only the fluorescence signals generated by being excited by the modulated laser can be amplified to improve the signal-to-noise ratio; and then, adding the FP interferometer to enter a receiving light path, and after the FP interferometer is added to enter the receiving light path, if the resonance frequency of the FP interferometer does not meet the target wavelength, the FP interferometer cannot receive signals in the first phase-locked amplifier, and modulating the FP interferometer to the required resonance frequency by observing the signals of the first phase-locked amplifier so as to realize narrow-band filtering of the fluorescent signals.
Further, the FP interferometer is subjected to wavelength scaling by utilizing a first phase-locked amplifier, the FP interferometer is scanned near the resonance frequency, a scanning signal of the FP interferometer is taken as a reference signal by a second phase-locked amplifier, and the output of the first phase-locked amplifier which receives a fluorescence signal obtained by laser pumping with modulation frequency and subjected to phase-locked amplification is taken as an input signal; only the fluorescent signal obtained by the laser pump with the modulation frequency can generate signal output in the first phase-locked amplifier, the signal output appears in the same frequency period of the scanning signal along with the resonance frequency scanning of the FP interferometer, the second phase-locked amplifier uses the scanning signal of the FP interferometer as the reference to carry out further phase-locked amplification, and the requirements for fine tuning and stable operation of the FP interferometer are reduced by using the double phase-locked amplifier.
The invention has the beneficial effects that:
the invention provides a narrow-band filtering system and a narrow-band filtering method for measuring a fluorescent signal by LIF (light-emitting diode) based on an FP (Fabry-Perot) interferometer, wherein the narrow-band filtering system and the narrow-band filtering method are characterized in that a proper free spectral region and fineness are selected through the design of an FP wavemeter, a phase-locked amplifier or a wavemeter is used for carrying out wavelength calibration on the FP interferometer by utilizing the tunable function of the resonance frequency of the FP interferometer, or another phase-locked amplifier is used for collecting signals, so that the narrow-band filtering of the fluorescent signal with the frequency. Under the condition that the performance of related domestic optical filtering products is insufficient, the existing domestic products with independent property rights are utilized to realize the narrow-band filtering performance of the specified wavelength of the bandwidth of 0.1-0.5nm required by LIF, the foreign monopoly and limitation are broken, and the international first-class narrow-band filtering performance is realized.
Drawings
FIG. 1 is a schematic diagram of LIF fluorescence measurement and FP interferometer phase-locked calibration principle;
FIG. 2 is a schematic diagram of a fluorescence signal receiving optical path;
FIG. 3 is a schematic diagram of the FP interferometer wavemeter calibration principle;
fig. 4 is a schematic diagram of a signal acquisition system of a double phase-locked amplifier.
Detailed Description
The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments, and all other embodiments obtained by a person skilled in the art based on the embodiments of the present invention belong to the protection scope of the present invention without creative efforts.
According to the embodiment of the invention, a narrow-band filtering system based on an FP interferometer is provided, and a receiving light path is shown in figure 1. And converging the isotropic fluorescent signals into parallel optical signals to be incident on the FP interferometer through a lens group. The transmission spectrum of the FP interferometer is collected by a sensor by using the FP interferometer which has a free spectral region and proper fineness (the free spectral region is about 1-2nm, the fineness is more than 30, namely the FWHM (full width at half maximum) of the resonance peak of the transmission spectrum of the interferometer is about 0.1-0.5 nm) and is tuned to a target wavelength, so that narrow-band filtering based on the fineness of the FP interferometer and under a corresponding bandwidth is realized. The resonance frequency of the FP interferometer is tuned by methods of changing the cavity length through stress, changing the incident light angle through rotation and the like, and the wavelength of the FP interferometer is calibrated by using a lock-in amplifier signal or a wavemeter, so that the FP interferometer meets the wavelength corresponding to a fluorescent signal, and the function of narrow-band filtering under the wavelength is achieved.
The specific embodiment of the invention is as follows: a narrow-band filtering system based on an FP interferometer comprises a laser source, wherein emitted laser signals enter a laser modulator, are modulated by the laser modulator and then are emitted into a plasma cavity, fluorescence signals are collected through an optical lens group, the optical lens group is connected to the FP interferometer, the FP interferometer is connected with a sensor, then the sensor signals are output to a phase-locked amplifier, and reference signals of the phase-locked amplifier are derived from modulation reference signals output by the laser modulator. According to the embodiment of the invention, the LIF fluorescence signal is isotropic fluorescence, so the receiving optical path needs to change the received point light source into a parallel light source through a proper optical lens group and then enter the FP interferometer. As shown in fig. 2, the present embodiment uses the convex lens group to perform parallel collimation of the light path, and any optical device combination capable of collimating the isotropic light source into a parallel light source can be used here. The LIF collection area fluorescence signal is incident on the FP interferometer in parallel. The FP interferometer should be fixed by a rigid shell, so that the stability of the resonance frequency of the FP interferometer during measurement is prevented from being influenced by the cavity length and the change of the incident angle of the FP interferometer due to installation, in addition, the relative positions of the FP interferometer, a lens group and a sensor are ensured to be fixed when the FP interferometer is used as a narrow-band light filtering system in consideration of the influence of the incident light angle on the resonance frequency of the FP interferometer, and the relative positions of the lens group, the FP interferometer and the sensor cannot be changed when the receiving position is adjusted by changing the position of the whole receiving light path and the focal length of the lens group. The method is the most direct tuning method, and requires that an assembly shell of the FP interferometer and an FP interferometer body are relatively fixed but have little influence on the FP interferometer, so that the fixation of the FP interferometer does not influence the cavity length modulation of the FP interferometer, the FP interferometer in a large free spectral range has a small cavity length and is easily influenced by factors such as assembly errors when controlled by piezoelectric ceramics, and the FP interferometer is difficult to be stabilized at a certain fixed resonance frequency by the aid of factors such as the capacitance of the piezoelectric ceramics and the ripple waves of a power supply. In addition, the cavity length of the FP interferometer can be changed by changing the temperature to tune the resonance frequency, the method requires that the assembly shell of the FP interferometer needs to have good heat conduction performance and good heat shield, the temperature distribution near the FP interferometer is uniform, the heat exchange between the whole system and the outside is weak, the fine and stable control of the temperature is realized, the method can ensure the stable work of the FP interferometer after adjustment, but the requirement on the accuracy of temperature feedback control is high, in addition, enough time is needed to reach the heat balance during tuning, the adjustment period is long, and the method is easily influenced by the outside environment including room temperature, humidity, seasonal variation and the like, and the stability is poor. The method can ensure the stable work of the FP interferometer after adjustment, but has higher precision requirement on a rotation adjusting mechanism. The resonance adjustment of the FP interferometer can also be carried out by changing the refractive index of the light-transmitting medium (the pressure is usually changed when the light-transmitting medium is gas, and methods for changing the refractive index of other media can be applied to the method). Other tunable FP interferometers can be used herein. The FP interferometer is subjected to wavelength calibration of resonance frequency by a lock-in amplifier method or a direct measurement method of a wavelength meter and the like, and the FP interferometer tuned to the resonance frequency consistent with the fluorescence wavelength is used for narrow-band filtering of the target wavelength and 0.1-0.5nm (depending on the fineness of the FP interferometer) nearby the target wavelength. And receiving the transmission spectrum of the FP interferometer by a sensor after the FP interference as a signal collection.
According to the basic principle of the FP interferometer,
wherein
Theta is the incident angle, lambda is the incident light wavelength, It,IiRespectively is the projection light intensity, the incident light intensity, h is the cavity length, n is the working mediumThe refractive index of the film is high,
r is a reflection rate of the light beam,
is the free spectral range.
For the fineness of the fringes, the resolution A of the FP interferometer is, according to the Rayleigh criterion
The modulation methods of the FP interferometer mainly include air pressure modulation (changing refractive index), cavity length modulation (changing cavity length), angle modulation (changing incident angle), temperature modulation (changing cavity length), and the like. For a certain FP interferometer, the free spectral range DeltaLambda can be changed by changing the cavity length h, the refractive index n of the working medium and the incident light angle through external stress (through piezoelectric ceramics, temperature control or other similar methods)fThereby changing the resonant frequency; the resolving power A is determined by a free spectral region and fineness which are determined by the reflectivity of a lens when the FP interferometer is designed and processed, and the resolving power of the FP interferometer can be changed by changing the cavity length h, the working medium refractive index n and the incident light angle through external stress (through piezoelectric ceramics, temperature control or other similar methods) to change the free spectral region, so that the narrow-band filtering bandwidth is changed. The model selection design of the FP interferometer needs to consider the free spectral region, the fineness and the like. The free spectral range and finesse of the FP interferometer determine the wavelength broadening of the narrow-band filtering system: the FP interferometer with smaller free spectral range and higher fineness has better resolution capability, can select the wavelength more finely by the FP interferometer, and improves the performance of a narrow-band filtering system.
According to the adjusting method and the requirements on the free spectral region and the fineness of the FP interferometer, the FP interferometer with the free spectral region of 15000GHz (about 9.5nm) and the fineness of 30 can realize narrow-band filtering with the bandwidth of about 0.3 nm. Different free spectral ranges and finesse can be employed for different target wavelengths and bandwidth requirements.
The method for realizing the filter of the specified wavelength by using the FP interferometer needs to accurately tune the resonance frequency of the FP interferometer and ensures that the required wavelength is met, and realizes the calibration of the resonance frequency of the FP interferometer or the signal acquisition by three methods:
method 1. the tuning of the resonant frequency is accomplished by the calibration of a wavemeter. The FP interferometer wavemeter calibration system is shown in FIG. 3. The wavelength corresponding to the resonance frequency of the FP interferometer can be determined by adopting a rare gas light source to enter the FP interferometer and using a wavelength meter to receive the transmission spectrum of the FP interferometer. The resonant frequency of the FP interferometer is tuned by adjusting the cavity length of the FP interferometer, so that a proper tuning position is selected to enable the resonant frequency of the FP interferometer to correspond to the wavelength of a fluorescence signal, an obvious peak value can be formed in a transmission spectrum only when light with the wavelength of the fluorescence wavelength and 0.3nm (depending on the fineness of the FP interferometer) near the fluorescence wavelength is used, a wavelength meter can measure an effective signal, and the FP interferometer can realize narrow-band filtering of a target wavelength at the moment.
Method 2, the calibration of the wavelength meter is considered to put higher requirements on the precision of the wavelength meter, and the calibration can also be carried out by utilizing a lock-in amplifier. The resonance frequency of the FP interferometer can be calibrated by a lock-in amplifier. The FP interferometer phase-locked scaling system is shown in figure 1. The input signal of the phase-locked amplifier is the fluorescent signal and the background light signal received by the sensor, the reference signal is the amplitude modulation signal output by the laser modulator, the phase-locked amplifier can perform phase-locked amplification on the signal with the same frequency as the laser after amplitude modulation, namely the output signal of the phase-locked amplifier mainly comes from the fluorescent signal generated by the laser pumping at the moment. Firstly, removing the FP interferometer in a receiving light path, modulating incident laser by using an amplitude modulator, and amplifying a signal with the same frequency as the incident laser by using a fluorescence signal received by a sensor by using a phase-locked amplifier. Because the physical process of laser induced fluorescence has certain time and the instruments such as the sensor also have response time, the phase of the phase-locked amplifier is adjusted at the moment, so that the output signal of the phase-locked amplifier at the current position is maximum. At this time, the whole receiving optical path is adjusted to maximize the output signal of the lock-in amplifier. And an FP interferometer is added between the lens group and the sensor in the light path, and the cavity length of the FP interferometer is adjusted to tune the resonance frequency of the FP interferometer. When the resonant frequency of the FP interferometer is tuned to a certain value, the signal of the sensor after passing through the lock-in amplifier is strongest, due to the characteristics of the lock-in amplifier, if the transmission spectrum of the FP interferometer at this time, that is, the optical signal received by the sensor is changed into light of other wavelengths due to improper tuning or disturbance of the FP interferometer, the signal will not have the same frequency and phase information as the fluorescent signal pumped by the amplitude modulation laser, and will be filtered at the lock-in amplifier, therefore, when the signal output by the lock-in amplifier is strongest, it can be considered that the wavelength corresponding to the resonant frequency of the FP interferometer at this time meets the wavelength required by narrow-band filtering.
3. The method 1 and the method 2 are used for designing the fine adjustment and stable operation of the FP interferometer, and if the FP interferometer has small deviation in an experiment or during the experiment, the signal-to-noise ratio, the signal intensity and the physical information contained in the signal can be greatly influenced. Method 3 provides a signal acquisition method based on a lock-in amplifier. A schematic diagram of a signal acquisition system according to method 3 is shown in fig. 4. Firstly, the FP interferometer is adjusted to the position of the phase-locked amplifier with signal output by using the method 2, the transmission spectrum comprises the continuous spectrum of background stray light and the characteristic spectrum of atomic luminescence and fluorescence, and only the fluorescence signal obtained by laser pumping under the modulation frequency can be amplified by the phase-locked amplifier in a phase-locked manner. Modulating the cavity length or the incident angle of the PF interferometer to enable the FP interferometer to scan the wavelength near the resonant frequency, enabling a fluorescence signal obtained by laser pumping with modulation frequency and subjected to phase-locked amplification by a phase-locked amplifier to appear in a transmission spectrum at the scanning frequency period of the FP interferometer, connecting another phase-locked amplifier (No. 2 phase-locked amplifier) to the output of the phase-locked amplifier, enabling the input of the No. 2 phase-locked amplifier to be the fluorescence signal obtained by laser pumping with modulation frequency and subjected to phase-locked amplification and output by the phase-locked amplifier, enabling a reference signal to be the FP interferometer scanning signal, adjusting the phase of the No. 2 phase-locked amplifier until the output of the No. 2 phase-locked amplifier is maximum, and enabling the output signal to be the fluorescence signal obtained by the laser pumping with modulation frequency. In the method 3, the fine and stable control on the tuning position of the FP is not needed, so that the realization difficulty is greatly reduced.
Although illustrative embodiments of the present invention have been described above to facilitate the understanding of the present invention by those skilled in the art, it should be understood that the present invention is not limited to the scope of the embodiments, and various changes may be made apparent to those skilled in the art as long as they are within the spirit and scope of the present invention as defined and defined by the appended claims, and all matters of the invention which utilize the inventive concepts are protected.
Claims (9)
1. A LIF measurement fluorescence signal narrow-band filtering system based on FP interferometer is characterized in that: the laser device comprises a laser source, wherein a laser signal emitted is emitted to a laser modulator, is modulated by the laser modulator and then is emitted to target particles, and a fluorescence signal is collected through an optical lens group, the optical lens group is connected to an FP interferometer, the FP interferometer is connected with a sensor, and then the sensor signal is output to a first phase-locked amplifier, and a reference signal of the first phase-locked amplifier is derived from a modulation reference signal output by the laser modulator;
the FP interferometer can change the self resonant frequency through tuning, the lens group or the optical component is used for collimating and parallelly inputting the fluorescent signal into the FP interferometer, the resonant frequency of the FP interferometer is tuned to the position equivalent to the specified wavelength through the first phase-locked amplifier and the wavelength meter, so that the FP interferometer generates a transmission spectrum for the incident light with the specified wavelength, and the narrow-band filtering with the frequency width of 0.1-0.5nm is realized;
or the second phase amplifier is used for signal acquisition, the FP interferometer is scanned and modulated in resonance frequency, the modulation signal of the FP interferometer is used as a reference signal, the LIF fluorescence signal which is output by the first phase-locked amplifier and is subjected to phase-locked amplification for the second time, and narrow-band filtering with the bandwidth of 0.1-0.5nm is realized by using the fineness of the FP interferometer.
2. The narrow-band filtering system for LIF measurement fluorescence signals based on FP interferometer of claim 1, wherein:
the optical lens group adopts a convex lens group to complete parallel collimation of a light path, so that fluorescent signals in an LIF collection area are incident into the FP interferometer in parallel.
3. The narrow-band filtering system for LIF measurement fluorescence signals based on FP interferometer of claim 1, wherein:
the FP interferometer is provided with a rigid shell for fixing the FP interferometer, so that the stability of the resonance frequency of the FP interferometer during measurement is prevented from being influenced by the cavity length and the change of the incident angle of the FP interferometer caused by installation, the relative positions of the FP interferometer, a lens group and a sensor are ensured to be fixed when the FP interferometer is used as a narrow-band light filtering system, and the position of the whole receiving light path and the focal length of the lens group are changed when the receiving position is adjusted, so that the relative positions of the lens group, the FP interferometer and the sensor cannot be changed.
4. The narrow-band filtering system for LIF measurement fluorescence signals based on FP interferometer of claim 1, wherein:
the FP interferometer can change the cavity length through piezoelectric ceramics to carry out resonance frequency tuning, or can change the cavity length of the FP interferometer through changing the temperature to carry out resonance frequency tuning, or can carry out resonance frequency adjustment of the FP interferometer through adjusting the incident light angle, or can carry out resonance adjustment of the FP interferometer through changing the refractive index of a light-transmitting medium.
5. The narrow-band filtering system for LIF measurement fluorescence signals based on FP interferometer of claim 1, wherein:
the wavelength calibration of the resonance frequency of the FP interferometer is carried out by a lock-in amplifier method or a direct measuring method of a wavelength meter, the FP interferometer tuned to the resonance frequency consistent with the fluorescence wavelength is used for carrying out narrow-band filtering on the target wavelength and 0.1-0.5nm nearby the target wavelength, and the transmission spectrum of the FP interferometer is received by a sensor after the FP interferometer is interfered and is used for signal acquisition.
6. The narrow-band filtering system for LIF measurement fluorescence signals based on FP interferometer of claim 1, wherein: when a second phase amplifier is used for signal acquisition, the oscilloscope is connected to a second phase-locked amplifier, and the second phase-locked amplifier is also connected to the first phase-locked amplifier and a modulation power supply of the FP interferometer respectively; the first phase-locked amplifier is connected to the FP interferometer sensor, and the reference signal of the first phase-locked amplifier is connected to the modulation reference signal output by the self-excitation light modulator.
7. The narrow-band filtering system for LIF measurement fluorescence signals based on FP interferometer of claim 1, wherein: the FP interferometer is rigidly connected with the lens group or the optical component and the sensor by a rigid shell of the FP interferometer, so that the cavity length and the incidence angle of the FP interferometer are not changed by a fixing mechanism, and the relative position of the components is not changed during measurement.
8. A method of narrow-band filtering of fluorescence signals for LIF measurements based on FP interferometers, using the system of any of the above claims 1-7, comprising the steps of:
LIF utilizes incident laser to actively excite target particles to an excited state, the target particles in the excited state can spontaneously jump to a low level to release photons to generate fluorescence signals, the incident laser is subjected to amplitude modulation through an acousto-optic modulator or electro-optic modulator modulation means, the modulation signals of the acousto-optic modulator or the electro-optic modulator are input into a first phase-locked amplifier to serve as reference signals, the first phase-locked amplifier of the reference signals is used for performing phase-locked amplification on the fluorescence signals received by a sensor, the phase-locked amplification and the reference signals have the same frequency and the same phase, and at the moment, only the fluorescence signals generated by being excited by the modulated laser can be amplified to improve the signal-to-noise ratio; and then, adding the FP interferometer to enter a receiving light path, and after the FP interferometer is added to enter the receiving light path, if the resonance frequency of the FP interferometer does not meet the target wavelength, the FP interferometer cannot receive signals in the first phase-locked amplifier, and modulating the FP interferometer to the required resonance frequency by observing the signals of the first phase-locked amplifier so as to realize narrow-band filtering of the fluorescent signals.
9. The method of claim 8, wherein: the method comprises the steps that a first phase-locked amplifier is used for calibrating the wavelength of the FP interferometer and scanning the FP interferometer near a resonance frequency, a second phase-locked amplifier takes a scanning signal of the FP interferometer as a reference signal, and the output of the first phase-locked amplifier which receives a fluorescence signal obtained by laser pumping with modulation frequency and subjected to phase-locked amplification is used as an input signal; only the fluorescent signal obtained by the laser pump with the modulation frequency can generate signal output in the first phase-locked amplifier, the signal output appears in the same frequency period of the scanning signal along with the resonance frequency scanning of the FP interferometer, the second phase-locked amplifier uses the scanning signal of the FP interferometer as the reference to carry out further phase-locked amplification, and the requirements for fine tuning and stable operation of the FP interferometer are reduced by using the double phase-locked amplifier.
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