Ultra-fast coherent Raman spectrometer based on quantum entanglement photon enhancement and light path device thereof

Abstract

The invention discloses an ultrafast coherent Raman spectrometer based on quantum entanglement photon enhancement and a light path device thereof, which realize ultrafast and high-resolution detection of a molecular vibration mode through integration of a quantum light source assembly, an ultrafast laser assembly, a light path assembly and a nonlinear crystal assembly and a high-sensitivity detection technology. By utilizing the characteristics of quantum entangled photons, the sensitivity and resolution of spectral measurement are improved, the system structure is simplified, and the cost is reduced. The quantum light source assembly adopts a nonlinear optical crystal to perform parametric down-conversion to generate entangled photon pairs. The ultrafast laser assembly generates femtosecond pulses, and the femtosecond pulses and the entangled photon pairs carry out nonlinear interaction. The light path assembly accurately controls the path and polarization state of photons to realize nonlinear Raman scattering of sample molecules. And the high-sensitivity detector is used for detecting and measuring the Raman light signal scattered by the sample. The invention aims to provide a spectral analysis method with high time resolution and high spectral resolution so as to realize ultrafast and high-resolution detection of a molecular vibration mode. According to the spectrograph, by utilizing the characteristics of quantum entangled photons, through entangled photon pairs generated by the nonlinear optical crystal, the sensitivity and resolution of spectral measurement are improved, and the problem of balance between time and spectral resolution in the prior art is solved.

Description

Technical Field

[0001] The invention relates to the technical field of optical instruments, and in particular to an ultrafast coherent Raman spectrometer based on quantum entanglement photon enhancement and an optical path device thereof. Background Art

[0002] In today's scientific research and industrial applications, the need for in-depth insights into the structure and dynamics of matter is becoming increasingly urgent, which not only promotes the rapid development of spectroscopy technology, but also puts higher requirements on the accuracy and resolution of Raman spectroscopy technology. As a non-destructive testing technology, Raman spectroscopy can provide detailed information about molecular vibrations, chemical bonds and material structures, and its application in chemical analysis, biomedical imaging and materials science is crucial. However, traditional coherent Raman spectroscopy techniques such as coherent anti-Stokes Raman scattering (CARS) and stimulated Raman scattering (SRS) often cannot achieve the best of both worlds in terms of temporal resolution and spectral resolution. This trade-off limits its potential in capturing and analyzing ultrafast molecular dynamics and precision material characterization, especially when studying fast chemical reactions, biomolecular interactions and internal dynamics of materials. Improved temporal resolution is crucial to revealing the detailed mechanisms of these processes. At the same time, high spectral resolution can provide more accurate molecular vibration information, which helps to distinguish and identify different components in complex chemical environments.

[0003] In addition, the existing Raman spectroscopy technology often faces the problem of low signal-to-noise ratio when detecting low-frequency vibration modes due to the presence of non-resonant background noise. These background noises are very close to the wavelength of the CARS signal and are difficult to eliminate by simple filtering methods, which seriously affects the quality and availability of the spectrum. In addition, the time resolution of traditional CARS technology is limited by the pulse width, making it difficult to capture ultrafast molecular dynamics at the femtosecond or sub-femtosecond level, and the spectral range obtained is limited. For samples containing multiple components or unknown components, multiple measurements or adjustments of laser parameters may be required, which is not only time-consuming but also inconvenient to operate.

[0004] The use of quantum entangled photons provides new possibilities for solving the above problems. The properties of quantum entanglement allow two or more photons to form a highly correlated joint state in frequency, time and space. This correlation can be used to improve the sensitivity and resolution of spectral measurements.

[0005] There is currently no specific method for how to actually apply quantum entanglement to Raman spectrometers and reduce non-resonant background noise to improve the signal-to-noise ratio. Therefore, in response to these challenges, the present invention innovatively proposes an ultrafast coherent Raman spectrometer based on quantum entangled photon enhancement and its optical path design. The invention uses the quantum correlation between quantum entangled photon pairs to achieve ultrafast, high-resolution detection of molecular vibration modes, demonstrating the ability to detect electronic coherence on a femtosecond scale, breaking through the limitations of traditional technology and solving the trade-off between time and spectral resolution. It also provides a new, cost-effective spectral analysis method that uses a single femtosecond laser and PCF to simplify the system structure and reduce costs compared to traditional time-resolved CARS spectroscopy systems. The development of this equipment will greatly promote the development of spectroscopic technology and bring revolutionary changes to fields such as chemical analysis, biomedical imaging, and materials science. Its importance is self-evident. By integrating innovative quantum light sources, ultrafast lasers, precision optical path control and high-sensitivity detection technology, this integrated quantum Raman spectrometer will provide more in-depth and more accurate analysis tools for scientific research and industrial applications, opening a new chapter in the exploration of the microscopic world. Summary of the invention

[0006] Problem that the invention aims to solve

[0007] Through the time and spectral resolution provided by quantum correlation that cannot be achieved by traditional classical pulses or non-entangled light fields, the optical path structure of the Raman spectrometer detection device under quantum entanglement is designed. And based on the traditional CARS signal is usually accompanied by non-resonant background noise, and the spectral range that can be obtained by a CARS measurement is limited, which leads to time-consuming and complex operation.

[0008] The present invention is accomplished in view of such problems, and its object is to provide a specific optical path design of an ultrafast coherent Raman spectrometer based on quantum entangled photon enhancement.

[0009] Solutions for solving problems

[0010] In order to solve the above problems, the optical path of the Raman spectrometer of the present invention comprises: a quantum light source component, an ultrafast laser component, an optical path component, a nonlinear crystal component, and a high-sensitivity detector component.

[0011] The quantum light source assembly includes a light source unit, a nonlinear optical crystal, a half-wave plate (HWP), a quarter-wave plate (QWP), a beam splitter, etc. The nonlinear optical crystal is used for parametric down-conversion to generate entangled photon pairs as ultrafast probe light.

[0012] The laser light source assembly includes a Ti:Sapphire femtosecond laser, which generates femtosecond pulses to pump an optical parametric oscillator (OPO) to generate Stokes light required in the CARS experiment, namely, pump and Stokes light, which interact nonlinearly with the entangled photon pairs.

[0013] The optical path setting includes a beam splitter (PBS), an interference filter, a reflector, a polarizer, etc., which are used to accurately control the path and polarization state of photons.

[0014] The nonlinear crystal is used to generate and manipulate quantum entangled photons and realize nonlinear Raman scattering with sample molecules.

[0015] The highly sensitive detector is used to detect and measure the Raman light signal scattered by the sample.

[0016] Entangled photon pairs are generated using quantum light source components, and parametric down-conversion is performed through nonlinear optical crystals (BBO crystals) to generate entangled photon pairs. These photon pairs have quantum correlations and can be used to improve the sensitivity and resolution of spectral measurements. As ultrafast probe light, the vibrational coherence of molecules can be studied by adjusting the time delay of photons. The CARS process is stimulated by supercontinuum spectroscopy, and time-resolved CARS is achieved by the time delay method. Ultrafast laser components, titanium sapphire lasers, are used to generate femtosecond laser pulses to pump photonic crystal fibers to generate supercontinuum spectra, and act on the sample as pump light and Stokes light at the same time to excite the molecular sample to an excited state. The entangled signal photons act as Raman probes, interact with the molecular sample, and the quantum state changes to form a quantum out-of-phase signal. At the same time, the idler photon is used as a reference. By adjusting the optical delay line to change the relative arrival time of the signal photon and the idler photon, the quantum interference effect is achieved to enhance the selectivity of the spectral signal, thereby obtaining more detailed information on the molecular correlation function.

[0017] The advantages of this patent are as follows:

[0018] An integrated quantum entanglement spectrometer has been developed, which integrates quantum light source, ultrafast laser, precision optical path control and high-sensitivity detection technology.

[0019] Precise control of photons can be achieved by precisely controlling the path and polarization state of photons through beam splitters, reflectors, polarizers, etc.

[0020] The use of quantum entangled photons in ultrafast coherent Raman spectrometers, combined with the time delay and frequency resolution capabilities of quantum entangled photons, enables ultrafast, high-resolution detection of molecular vibration modes, improving measurement performance. The quantum interference effect is also used to enhance the selectivity of spectral signals, improving the signal-to-noise ratio and accuracy of measurements.

[0021] Compared with the traditional time-resolved CARS spectroscopy system, this invention uses a single femtosecond laser and photonic crystal fiber (PCF), simplifies the system structure, and provides a cost-effective spectral analysis.

[0022] The specific optical path design and implementation method of an ultrafast coherent Raman spectrometer based on quantum entangled photon enhancement of the present invention are further described in detail below in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Specific optical path design of ultrafast coherent Raman spectrometer based on quantum entangled photon enhancement

[0024] Figure 2 Coherent Raman scattering principle

[0025] Figure 3 Interference preservation of entangled photon HOM effect

[0026] Figure 4 Entangled photon HOM effect interference destructive Specific implementation plan

[0027] Hereinafter, description will be given based on preferred embodiments with reference to the drawings.

[0028] The present invention adopts a wide-band photon emission system. Wide-band photons can cover a wider spectral range, which helps to capture richer molecular vibration information. The combination of wide-band photons and ultrafast pumping and detection technology can further improve the time resolution. At the same time, quantum entangled photon pairs provide additional control knobs. By adjusting the arrival time and bandwidth of photons, the relaxation and radiation processes of molecules can be selectively manipulated.

[0029] Figure 1In this paper, we selected a continuous wave laser with a wavelength of 355nm as the pumping light source. This wavelength can effectively interact with the nonlinear optical crystal to achieve an efficient spontaneous parametric down-conversion (SPDC) process. The nonlinear optical crystal in the quantum light source assembly uses a BBO (β-BaB2O4) crystal, and the phase matching angle of the crystal is precisely set to 36° to meet specific energy and momentum conservation conditions. In order to turn off the SPDC process and deduct background counts during the experiment, a 355nm half-wave plate is placed in front of the crystal. The pump light absorption cell is used to collect pump photons that have not undergone spontaneous parametric down conversion. The crystal has a high nonlinear coefficient and good optical uniformity, which is conducive to improving the efficiency of the SPDC process and can effectively generate wide-band entangled photon pairs. These photon pairs cover a wide spectral range, and due to the group velocity dispersion in the nonlinear crystal, time delay can be achieved by adjusting the length of the crystal. By precisely controlling the polarization state of the pump light and the phase matching conditions of the crystal, we can generate entangled photon pairs with quantum correlation characteristics in a wide band. The spectral distribution of these photon pairs extends from the visible to the near-infrared region, covering a bandwidth of 259 nm, thus providing an effective light source for wide-spectrum calibration of photodetectors.

[0030] The combination of half-wave plate and quarter-wave plate can accurately control the polarization state and path of the output photon pair to meet different experimental requirements. The 355nm cut-off filter and narrow-band interference filter can effectively filter out crystal scattered light and ambient stray light to ensure high purity of the spectrum, thereby improving the signal-to-noise ratio and accuracy of the measurement.

[0031] The beam splitter is used to separate the pump light from the generated entangled photon pairs, ensuring that the detector only receives the entangled photon pairs. The lens system includes a focusing lens and a collimating lens, which are used to adjust the size and direction of the light beam and improve the collection efficiency and stability of the system.

[0032] Using a highly sensitive photomultiplier tube (PMT) as a detector, it has high quantum efficiency and low dark count rate, thereby improving the sensitivity to light signals, reducing the noise of the detector itself, improving the signal-to-noise ratio, and being able to quickly respond to light signals and accurately detect single photon events. And PMT can handle light signals from very weak to relatively strong, with good stability and reliability. Compared with other types of high-sensitivity detectors, PMT provides a good balance between performance and cost.

[0033] These entangled photon pairs are used as Raman spectroscopy probes, and after time delay, specific

[0034]

[0035] The time delay is introduced by describing the time difference between the signal photon and the idler photon and the SPDC pump field. This time delay is introduced by the phase matching condition Δk(ω s ,ω i )L, where L is the length of the crystal, E0 is the pump-driven SPDC process,

[0036]

[0037] Where T s (T i ) is the time delay between the photons in the s (reference) arm and the SPDC pump field in the nonlinear crystal. ω0 / 2 is the central frequency of the down-converted beam. To monitor ultrafast electron coherence dynamics in molecular excited states, the probe pulse is activated after a delay T after the resonant photoexcitation or excited state propagation, e.g. Figure 2 As shown, when the S-arm photons scatter the excited state coherence, a Raman signal is generated.

[0038] With the help of entangled photons, by measuring the photon scattering signals at different times and frequencies, the interaction and dynamic information between the electronic states inside the molecule can be obtained, as follows,

[0039]

[0040] S QE (ω,ω i , T) This is the intensity-dependent expression of the QFRS signal, expressed as frequency ω and ω i and a function of the time delay T. This signal describes the response of the molecule to photon scattering at a specific frequency and time delay. N(N-1) is the second-order term for the number of molecules, |E s,ω | 6 |E i,ω | 2 The squares of the electric field amplitudes of the signal and idler photons are represented, and the higher powers of these electric fields represent the strength of the photon-molecule interaction in nonlinear processes. is the sum of all possible electronic transitions e', where α e,e’ is the transition polarizability from electronic state e to e', indicating the contribution of the internal electronic transition of the molecule to the signal. e,e’ (T) is the Raman line shape function, which describes the coherence relationship between electronic states at time T. It contains the time evolution information of electronic coherence and is the key to understanding the internal dynamics of molecules. The details are as follows:

[0041]

[0042] After the signal photon interacts with the sample, it interferes with another photon (idler photon) that did not directly interact with the sample in a Mach-Zehnder interferometer. In the interferometer, part of the S-arm photons is split off, and part of the photons is guided to propagate freely, and then mixed with the signal photons scattered by the sample as reference photons to interfere. This interference is a characteristic of quantum mechanics. Due to the quantum entanglement of the two photons, their wave functions are correlated, resulting in an interference pattern at the detector. When two entangled photons arrive at the same beam splitter at the same time, the HOM effect occurs, which is a quantum interference phenomenon that causes a decrease in the photon count rate recorded by the detector under certain conditions. The use of the HOM effect involves adjusting the optical delay line to change the relative arrival time of the signal photon and the idler photon to achieve a quantum interference effect.

[0043]

[0044] Among them, P coincidence is the probability that two detectors record a photon at the same time, is the phase difference between the two photons in the beam splitter.

[0045] This can be expressed by the following formula:

[0046]

[0047] Among them, ΔT is the time difference between the two photons arriving at the beam splitter, Δλ is the wavelength difference, and c is the speed of light.

[0048] When ΔT is very small, close to zero, the phase difference between the two photons at the beam splitter is Close to zero or π, then P coincidence Minimum, HOM effect occurs.

[0049] When two entangled photons enter the beam splitter at the same time, the superposition of their wave functions results in a specific interference pattern. At certain points in time, the wave functions of the two photons constructively interfere, causing the photon count rate recorded by the detector to increase by as much as Figure 3 At other times, the wave functions interfere destructively, causing the photon count rate recorded by the detector to decrease, such as Figure 4 .

[0050] By precisely controlling the time delay of the photons, the destructive interference points in the interference pattern can be adjusted. Because these noises usually do not show the same temporal correlations as the entangled photons, the HOM effect can be used to distinguish between resonant signals and non-resonant background noise, improving the selectivity of the spectrum.

[0051] By using a Mach-Zehnder interferometer, the path and time delay of photons can be precisely controlled, thereby using the HOM effect to distinguish resonant signals from non-resonant background noise. By using quantum interference, the selectivity of the spectrum can be improved, and high-resolution detection of molecular vibrations and electronic coherence can be achieved, which is unattainable with traditional classical light.

[0052] Furthermore, the role of the signal photon and the idler photon. The signal photon participates in the generation of Raman scattering signals through nonlinear interactions with the sample molecules, thereby carrying important information about the vibration modes of the sample molecules. The idler photon, as a reference photon, provides precise control of the phase and frequency of the signal photon through quantum correlation with the signal photon, thereby enhancing the resolution of the spectrum and the accuracy of the measurement.

[0053] Figure 1 The beam splitter in the mid-optical path component is used to split the pulsed laser of the laser light source into two parts, one part is used to excite quantum entangled photons, and the other part is used to pump the photonic crystal fiber (PCF).

[0054] The present invention uses a Ti:Sapphire femtosecond laser to pump a photonic crystal fiber (PCF) to generate a supercontinuum spectrum, which is used to receive laser pulses generated by a laser light source unit and generate a supercontinuum spectrum covering a wide spectral range. The supercontinuum spectrum is used as pump light and Stokes light in a CARS process.

[0055] Femtosecond laser pulses are passed through an optical isolator to ensure that the light in the optical path can only propagate in one direction, preventing backscattered light from entering the laser system. The interference filter divides the laser into two parts. One part of the light is coupled into the optical parametric oscillator (OPO) through an aspheric mirror with a numerical aperture of 0.65NA to generate the Stokes light required for CARS. The combination of OPO and quantum entangled photons enables it to provide a wider spectral range and higher time resolution, and also simplifies the system structure and reduces costs.

[0056] Furthermore, a PCF with a length of 480nm and a zero dispersion wavelength of 840nm produces a supercontinuum spectrum. The other part passes through a wide-band photon output system to generate entangled photons. Inside the PCF, due to the nonlinear effect, the input pulsed light is expanded to a wider spectral range in the optical fiber to form a supercontinuum spectrum. It can cover a variety of molecular vibration modes, increase the detection spectral range, and the supercontinuum spectrum has ultra-fast time characteristics, which helps to achieve femtosecond-level time resolution and capture fast molecular dynamics. In addition, PCF has a strong nonlinear effect, which helps to generate Raman scattering signals of sufficient intensity. By adjusting the parameters of the PCF and the pumping conditions, the generated spectral characteristics can be precisely controlled, thereby optimizing the detection conditions of the Raman spectrum.

[0057] Furthermore, the supercontinuum spectrum is collected by the microscope objective at the output end of the PCF, collimated, and then passed through a long-wave pass filter with a cutoff wavelength of 800nm ​​to generate the pump light and Stokes light required for the CARS process. The focusing lens and objective lens are used to focus the supercontinuum spectrum and the detection light onto the sample. The sampling mirror with a reflectivity of 5% is used to separate a part of the supercontinuum spectrum from the main light path to monitor the spectral broadening of the supercontinuum spectrum and the intensity fluctuation of each spectral band in real time, so as to more conveniently adjust and optimize the experimental system.

[0058] Furthermore, the entangled photons generated by another part of the femtosecond laser pulses are delayed by adjusting the length of the BBO crystal to achieve the quantum interference effect.

[0059] Furthermore, the entangled photon pair is irradiated onto the sample, and the signal photon interacts nonlinearly with the sample molecules to generate a Raman signal. In the Mach-Zehnder interferometer, the signal photon interferes with the idler photon, and the interference pattern is recorded by the detector.

[0060] Furthermore, detector 1 records the interference term and detector 2 records the number of idler photons to achieve joint detection. This detection method can provide detailed information about the molecular vibration and electronic coherence of the sample. And through the Mach-Zehnder interferometer, the full transient coherent dynamics including phase and intensity can be observed, including the rapid oscillation and decay of electronic coherence.

Claims

1. An ultrafast coherent Raman spectrometer based on quantum entangled photon enhancement and its optical path device, characterized in that: Including quantum light source components, ultrafast laser components, optical path components, nonlinear crystal components, and high-sensitivity detector components. The quantum light source assembly includes a light source unit, a nonlinear optical crystal, a half-wave plate (HWP), a quarter-wave plate (QWP), a beam splitter, etc. The nonlinear optical crystal is used for parametric down-conversion to generate entangled photon pairs as ultrafast probe light. The laser light source assembly includes a titanium sapphire femtosecond laser, which generates femtosecond pulses for pumping and Stokes light, and performs nonlinear interaction with entangled photon pairs. The optical path setting includes a beam splitter (PBS), a reflector, a polarizer, etc., which are used to accurately control the path and polarization state of photons. The nonlinear crystal is used to generate and manipulate quantum entangled photons and realize nonlinear Raman scattering with sample molecules. The highly sensitive detector is used to detect and measure the Raman light signal scattered by the sample.

2. A method for ultrafast coherent Raman spectroscopy measurement using the spectrometer according to claim 1, characterized in that: a) generating entangled photon pairs with quantum correlation using a quantum light source assembly, wherein the quantum light source assembly comprises a nonlinear optical crystal, a half-wave plate, a quarter-wave plate and a beam splitter; b) generating femtosecond pulses using an ultrafast laser assembly, wherein the ultrafast laser assembly includes a Ti:Sapphire femtosecond laser for pumping an optical parametric oscillator to generate Stokes light required in a CARS experiment; c) controlling the path and polarization state of the entangled photon pair through an optical path component, wherein the optical path component includes a beam splitter, an interference filter, a reflector and a polarizer; d) irradiating the entangled photon pair onto a sample, wherein the signal photon nonlinearly interacts with the sample molecule to generate a Raman scattering signal, and the idler photon serves as a reference; e) adjusting the optical delay line to change the relative arrival time of the signal photon and the idler photon to achieve the quantum interference effect, thereby enhancing the selectivity of the spectral signal; f) using a high-sensitivity detector assembly to detect and measure the Raman light signal scattered by the sample, wherein the high-sensitivity detector is a photomultiplier tube for recording the interference pattern; g) Analyze the interference pattern recorded by a highly sensitive detector to obtain detailed information about the molecular vibrations and electronic coherences of the sample.

3. The method according to claim 2, characterized in that: This involves adjusting the optical delay line to change the relative arrival time of signal photons and idler photons to achieve a quantum interference effect.

4. A method for processing ultrafast coherent Raman spectroscopy signals obtained based on the method of claim 3, characterized in that: The method comprises the following steps: a) collecting the interference signal recorded by a high-sensitivity detector; b) Apply signal processing techniques, such as Fast Fourier Transform (FFT), to analyze the time dependence of the interference signal; c) determining the vibration frequency and coherence time of the sample molecules according to the time and frequency characteristics of the interference signal; d) Using the evolution information of quantum states, reconstruct the interaction and dynamic process between the electronic states inside the molecule; e) Identify and distinguish the non-resonant background noise from the resonant Raman signal by comparing the interference signals under different time delays; f) Using the time and frequency correlation of quantum entangled photons to improve the signal-to-noise ratio and resolution of the spectrum; g) Analyze and characterize the chemical composition and structure of the sample based on the obtained spectral data.

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