H2O phase change detection method based on pumping-sum frequency detection technology

Abstract

The invention provides an H2O phase change detection method based on a pumping-sum frequency detection technology, and relates to the field of spectral analysis and precise temperature control. According to the method, a set of pumping-sum frequency detection system construction process comprising a laser emission module, a light beam modulation module, a main temperature control system, a signal acquisition system and a synchronous controller is designed, and excitation and sum frequency detection of interface water molecule vibration energy level transition are realized by using three beams of laser with specific wave bands and polarization characteristics. By accurately controlling the laser pulse time delay and condensation temperature control process, sum frequency spectrum signals of different time nodes are collected, and real-time monitoring and reconstruction of vibration spectrum dynamic evolution in the H2O phase change process are achieved by combining spectrum fitting and time sequence integration. The device has the advantages of being high in time resolution, high in spectral sensitivity, capable of obtaining molecular scale phase change information in real time and the like, and is suitable for H2O phase change condensation kinetic research, high-precision dew point measurement, humidity calibration and other scenes.

Description

TECHNICAL FIELD

[0001] The application relates to the fields of intelligent manufacturing, optoelectronics, precision instruments and metrology, and in particular to a method for detecting H2O phase transition based on pump-and-frequency detection technology. BACKGROUND

[0002] H2O phase transition is an inevitable part of the water cycle in nature, and the interface between the gas phase and the condensed phase is an important entry point for studying the behavior of H2O phase transition. In the phase transition process, the dynamic change of the hydrogen bond network is the core mechanism of energy dissipation. The vibration mode closely related to intermolecular interaction is selected as the experimental breakthrough window to further explore the dynamic mechanism of H2O in the phase transition process.

[0003] Dew point temperature measurement is widely recognized as the most accurate method in current humidity measurement, and is also the core basis for international humidity value transfer. Traditional dew point measurement methods mainly include the cold mirror method, the metal oxide method and the resonance method. However, these methods lack a deep understanding of the dynamic process of H2O phase transition, and usually need to measure after the water vapor condensation reaches a certain accumulation amount. This characteristic causes the traditional method to be unable to quickly and accurately determine the state of H2O in the dynamic phase transition process, thereby causing certain system errors and measurement hysteresis. Therefore, in-depth analysis and reconstruction of the dynamic process of H2O phase transition are of great significance for realizing accurate measurement and control of the dew point temperature.

[0004] The pump-and-frequency detection technology is a technology for studying the ultrafast phenomena of gas-liquid interface molecules by using ultra-short laser pulses. By taking the intersection point of the gas phase and the condensed phase as the entry point, the pump-and-frequency detection technology can be used to study the dynamic behavior of H2O phase transition, which can reveal the internal mechanism of the vibration energy level transition of H2O molecules, has ultra-high time resolution, and can achieve ultra-high sensitive resolution in the dynamic testing and calibration of H2O phase transition. SUMMARY

[0005] 1. Object:

[0006] The application provides an H2O phase transition detection method based on pump-and-frequency detection technology, which can detect the H2O phase transition behavior in real time and accurately during the occurrence of H2O phase transition.

[0007] 2. Technical solution:

[0008] One aspect of the application discloses an H2O phase transition detection method based on pump-and-frequency detection technology, and the operation process of the method is as shown in Figure 1 The specific steps are as follows:

[0009] Step 1: Construct a pump-and-frequency detection optical path system, as shown in Figure 2As shown, the system should include an ultrafast pulsed laser emission module 1 for subsequent laser conversion to generate corresponding incident pump and probe beams; the wavelength is 800±30 nm, the pulse duration is 0.1-3 ps, the repetition frequency is 1-10 MHz, and the single-pulse energy of the laser is 10 μJ-20 μJ.

[0010] The beam splitting and coupling element 2 splits and couples the light beams emitted by the light emission module into the corresponding subsequent light modulation modules 3, 4 or 5 to obtain three corresponding incident light beams, and the three light beams have different optical properties.

[0011] The infrared pump light modulation module 3 converts the light beams emitted by the light emission module into infrared pump light beams and modulates the optical properties thereof, and the wavelength of the pump light beams should cover a certain vibration energy level absorption band of the hydrogen-oxygen bond of the interface water molecules being researched (such as the hydrogen-oxygen bond of the bulk phase 1600 cm -1 , 3100-3500 cm -1 , and the free hydrogen-oxygen bond of the interface 3700 cm -1 ); the wave number is 3700-1500 cm -1 , (about 2.7-6.7 μm), the pulse duration is 0.1-3 ps, the repetition frequency is 1-10 MHz, and the single-pulse energy of the laser is 1 μJ-5 mJ.

[0012] The infrared probe light modulation module 4 converts the light beams emitted by the light emission module into infrared probe light beams and modulates the optical properties thereof, and the covered band of the infrared probe light beams is consistent with that of the pump light; the wave number is 3700-1500 cm -1 , (about 2.7-6.7 μm), the pulse duration is 0.1-3 ps, the repetition frequency is 1-10 MHz, and the single-pulse energy of the laser is 1 μJ-5 mJ.

[0013] The narrow-band visible light modulation module 5 converts the light beams emitted by the light emission module into narrow-band visible light beams and modulates the optical properties thereof; the wavelength is 400-800 nm, the pulse duration is 0.1-3 ps, the repetition frequency is 1-10 MHz, and the single-pulse energy of the laser is 1 μJ-5 mJ.

[0014] The main temperature control system 6 is used for controlling the temperature and actively controlling the phase change of H2O; the signal detection and acquisition module 7 is used for acquiring the output sum-frequency spectrum signal; the synchronous signal controller 8 is used for controlling the relative time delay of the incident pulses, as well as the main temperature control system and the spectrum acquisition system; the time delay between the pump light and the probe light is controlled to be 0.5-5 ps. In the optical system, the pump light and the probe light between the devices can be transmitted by optical fiber transmission devices to reduce the adjustment difficulty of the system optical path and improve the system stability and anti-interference ability.

[0015] Step 2: Experimental preparation and environmental control: initialize the laser, spectrometer, main temperature control system and synchronization controller. Preheat the laser, calculate and adjust the coupling angle of the three incident beams, irradiate the target sampling point, and obtain the background noise spectrum image of the experimental environment. Pre-set the delay time of each signal of the synchronization controller, control the relative time delay of the incident pulse through the synchronization controller, and control the main temperature control system and the spectrum acquisition system.

[0016] Step 3: Signal acquisition: control the time delay in the pump-probe system based on the joint control program, control the main temperature control system to start the phase change control system, and collect the light signal corresponding to the time delay through the CCD spectrometer and record it. Then change the relative delay time of each incident laser pulse through the synchronization controller, and repeat the spectrum acquisition process. Since the H2O condensation phase change is a dynamic process, it is necessary to ensure the consistency of the cooling rate and the initial node of the spectrum acquisition in each repeated measurement process.

[0017] Step 4: Data processing: after obtaining the spectrum data corresponding to different time delays, integrate and synthesize the final time-resolved spectrum data according to the acquisition time node, analyze the spectrum feature peak change according to the time delay, analyze the H2O phase change sensitivity, and summarize the phase change rule.

[0018] The advantages and beneficial effects of the present application are as follows:

[0019] The method designs a pump-and-frequency detection system construction process including a laser emission module, a beam modulation module, a main temperature control system, a signal acquisition system and a synchronization controller. Three laser beams with specific waveband and polarization characteristics are used to realize the excitation and frequency detection of the interface water molecule vibration energy level transition. By accurately controlling the laser pulse time delay and the condensation temperature control process, the frequency spectrum signal at different time nodes is collected, combined with spectrum fitting and time sequence integration, the real-time monitoring and reconstruction of the vibration spectrum dynamic evolution in the H2O phase change process are realized. The present application has the advantages of high time resolution, strong spectral sensitivity, real-time acquisition of molecular scale phase change information, etc., and is suitable for H2O phase change condensation dynamics research, high-precision dew point measurement and humidity calibration scenes. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is the operation process of the method of the present application.

[0021] Figure 2 is a schematic diagram of the pump-and-frequency detection system of the present application.

[0022] Figure 3 is a schematic diagram of the pump-and-frequency detection system optical path and signal acquisition of the present application.

[0023] Figure 4 is a schematic diagram of a signal acquisition control method of the method of the present application.

[0024] Figure 5 is a flow chart of a signal acquisition control method of the method of the present application. DETAILED DESCRIPTION

[0025] The above is the core idea of the present application. In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the technical solutions will be clearly and completely described below in combination with the embodiments of the present application. Obviously, the described embodiments are only one implementation example of the present application, rather than all the embodiments.

[0026] The embodiments of the present application disclose a method for H2O phase change detection based on pump-and-frequency detection. The present application is further described with reference to the accompanying drawings.

[0027] Step 1-1: Construct the input laser module required by the pump detection system according to the schematic diagram shown in Figure 2 . The laser light source can be selected as a titanium sapphire laser with a center wavelength of 800 nm and a pulse width of about 0.5 ps;

[0028] After beam splitting, one of the beams passes through an optical parametric amplification system to expand the wavelength to the infrared band. The expanded infrared light acts as pump light to excite the vibrational energy level transition of water molecules. Therefore, the pump light band covers the response wavelength of the water molecule vibration mode and the interface free hydrogen bond response wavelength, with a center wave number of about 2500 cm -1 , a spectral width of about 400 cm -1 , and a single pulse energy of about 12 μJ;

[0029] The other beam also expands the wavelength to cover the infrared band by passing through an optical parametric amplifier, with a center wave number of about 3000 cm -1 , a spectral width of about 200 cm -1 , and a single pulse energy of about 6 μJ;

[0030] Finally, one beam passes through a standard pulse shaper to expand the pulse to compress the spectrum, obtaining a beam with a center wavelength of 800 nm and a spectral width of about 15 cm -1 as a visible light probe, with a single pulse energy of about 10 μJ.

[0031] Step 1-2: Construct a condensation and sensing module with a main control temperature function to control the phase change of H2O. During the cooling process, when the temperature of the air in the free space decreases to the dew point, water vapor begins to condense to form tiny water droplets or fog droplets, which increase the condensation nuclei on the condensation surface to accelerate condensation and reduce the influence of supercooling effect. The main control temperature system controls the condensation surface temperature within ±1℃ of the dew point temperature, and the cooling rate is controlled at 0.1℃ / min.

[0032] The pump-probe H2O phase transition system is combined with the excitation probe laser module, and the optical path time delay, temperature control start and spectrum acquisition start modules in the system are connected with a synchronous controller, and the modules are controlled by a control program.

[0033] The hollow reflector in the optical path is selected to control the optical path time delay, and the relative position of the electric displacement table is controlled by the synchronous controller to produce ultra-high precision time delay between the light beam pulses.

[0034] Step 2: Experimental environment preparation and control: Set the key parameters of the experimental environment, collect the background noise as the baseline, and ensure the accuracy and repeatability of the experimental data.

[0035] In addition, after obtaining the three incident beams, the linear polarization state of the three beams is set, a half-wave plate is added to the optical path to change the linear polarization direction of the input laser, and the corresponding half-wave plate is rotated to set the pump infrared light and the probe infrared light to p-polarization (the polarization direction is parallel to the light and the normal plane), and the visible light is set to s-polarization (the polarization direction is perpendicular to the light and the normal plane).

[0036] The angle between the pump light incident axis and the detection plane is 56°, the angle between the probe infrared light incident axis and the normal of the detection plane is 40°, the angle between the visible light incident axis and the normal of the detection plane is 70°, and the angle between the sum frequency signal output beam and the normal of the detection plane is about 60°. The probe receiver is set near the exit direction at this angle for signal collection, and the optical path system is as shown in Figure 3 .

[0037] Step 3: Set the zero delay time between the infrared probe light and the visible light in the time domain, and set the positive delay time between the pump light and the probe light in the time domain as 0.5 ps, that is, the synchronous controller controls the electric displacement table (motion controller) of the probe light path to drive the hollow reflector to translate along the optical axis by 75 μm, at the same time, controls the main control temperature system to start the phase transition control system, and collects the corresponding spectral information through the spectrometer, and then resets the time delay line, temperature control module and spectrum acquisition module in the system; change the relative time delay to 1 ps, and the synchronous controller controls the electric displacement table of the probe light path to drive the hollow reflector to translate along the optical axis by 150 μm; at the same time, control the main control temperature system to restart, and repeat the spectrum acquisition process; in each repeated measurement and collection process, ensure that the cooling rate and the initial node of the spectrum acquisition are consistent, and at the same time, the influence of the background image noise in each measurement process needs to be excluded. The spectrum signal acquisition process and program are as shown in Figure 4 and Figure 5 .

[0038] Similarly, the time delay is increased step by step with a time step of 0.5 ps, and the above operation steps are cycled to collect 10 spectra.

[0039] Step 4: Demodulation of spectral signal phase change information reconstruction

[0040] After obtaining the spectral data corresponding to different times, the Lorentz distribution curve fitting is performed on each set of vibration spectral data signal, then according to the time node corresponding to each spectrum, the final synthesized time-resolved spectrum is output by sorting and integrating according to the time delay, and the condensation phase change process is reconstructed.

[0041] The above is a further detailed description of the present application in combination with specific embodiments, and the specific implementation of the present application cannot be limited to these descriptions. For ordinary skilled persons in the technical field to which the present application belongs, without departing from the concept of the present application, a number of simple deductions or substitutions can be made, which should be regarded as falling within the protection scope of the present application.

Claims

1. A method for detecting H2O phase transition based on pump-and-probe technique, characterized in that: Step 1: constructing a pump-and-frequency detection light path system, including: an ultrafast pulsed laser emission module for generating a laser beam with a central wavelength of 800±30 nm, a pulse width of 0.1-3 ps, a repetition frequency of 1-10 MHz, and a single pulse energy of 10-20 μJ; a beam splitting and coupling element for splitting and coupling the laser beam to three modulation modules; an infrared pump light modulation module for converting the split laser beam into pump light with a wavelength range of 2.7-6.7 μm (equivalent to 1500-3700 cm -1 ) and the laser pulse characteristics; an infrared probe light modulation module for generating probe infrared light with the same waveband as the pump light; a narrow-band visible light modulation module for generating visible light with a wavelength of 400-800 nm and a spectral width of about 15 cm -1 ; a main temperature control system for controlling the phase change process of H2O in the sample area, controlling the temperature within a range of dew point ±1℃, and controlling the cooling rate at 0.1℃ / min; a signal acquisition module for acquiring signals generated by the sum frequency process of the three beams at the sample; and a synchronous controller for controlling the relative time delay between the three beams and coordinating the synchronous operation of the temperature control system and the signal acquisition. Step 2: Experimental preparation and background noise acquisition, including initializing the laser, setting the incident angle and polarization direction of the light beam, setting the delay of the synchronous controller and collecting the baseline of the background noise; Step 3: Signal acquisition process, including: setting the zero time delay between the infrared probe light and the visible light, and setting the positive time delay between the pump light and the probe light; adjusting the electrically controlled delay line through the synchronous controller to set the time delay in the range of 0.5-5 ps; starting the main temperature control system to induce H2O condensation phase transition, and recording the sum frequency signal spectrum through the CCD spectrometer; repeating the above steps and sequentially increasing the time delay to collect spectrum data at multiple time nodes; Step 4: Spectrum data processing process, including: Lorenz function fitting for each group of spectra; integrating according to the time delay to reconstruct the time-resolved infrared sum frequency spectrum; extracting the dynamic change characteristics of the spectrum in the H2O phase transition process to realize the determination and reconstruction of the phase transition behavior.

2. The method of claim 1, wherein: The infrared pump light wave band covers 1600cm -1 or 3100~3500cm -1 Region to stimulate the characteristic wave band of the body phase hydrogen bond, or cover 3700cm -1 To stimulate the interface free hydrogen bond.

3. The method of claim 1, wherein: The condensation interface of the main temperature control system is provided with artificial micro-nano structure condensation nuclei to reduce the supercooling threshold of water vapor condensation and enhance the phase transition response sensitivity.

4. The method of claim 1, wherein: The synchronous controller controls the electrically controlled displacement table on the probe light path to realize the time delay adjustment of the laser pulse by driving the hollow retroreflector to translate along the optical axis direction, and the displacement accuracy is better than 0.1 μm.

5. The method of claim 1, wherein: In the spectrum data fitting process, multiple sets of Lorenz functions are used to separate and fit the multi-peak structure in the sum frequency spectrum, and the peak position, peak width and intensity are extracted as the phase transition dynamic indicators.

6. The method of claim 1, wherein: The three incident light beams have different polarization directions, in which the infrared pump light and the infrared probe light are p-polarized, and the visible probe light is s-polarized, and the sum frequency signal is emitted at a specific angle and collected by the detector.

Images