Raman spectrum system with optical parametric amplification and enhancement

Abstract

The invention provides an optical parametric amplification enhanced Raman spectrum system, which comprises a laser, after the laser is split by a spectroscope, one path of laser firstly passes through a lens, enters an optical parametric oscillator, then sequentially passes through a filter, the lens, a sample and the filter, and is combined with the other path of laser by a beam combiner; the combined laser is focused on the fan-shaped superlattice through the lens, passes through the acousto-optic tunable filter and then collects signals through the detector. The detection sensitivity of the Raman material can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the field of Raman detection technology, and particularly to a Raman spectroscopy system enhanced by optical parametric amplification. Background Art

[0002] Raman spectra is a kind of scattering spectrum. Raman spectroscopy analysis method is based on the Raman scattering effect discovered by Indian scientist Raman. It analyzes the scattering spectrum with a different frequency from the incident light to obtain information on molecular vibration and rotation, and is an analysis method applied to molecular structure research. The displacement and intensity of Raman spectra are related to the vibration and rotation energy levels of the sample. Therefore, Raman spectra can be used as the characteristic spectra of substances to calibrate substances.

[0003] However, for different substances, they have different transmission wavelengths. For example, quartz crystals are transparent in the visible light wavelength range but opaque in the mid-infrared band; germanium crystals are transparent in the mid-infrared band and opaque in the visible light band. In order to measure the Raman spectra of multiple substances, the method of replacing multiple lasers for use is usually adopted.

[0004] In addition, the Raman effect belongs to the third-order nonlinear effect and the intensity is very weak. It requires strong laser irradiation, and the obtained Raman spectra are also very weak, requiring a very sensitive Raman spectrometer for detection. In order to obtain high-intensity Raman spectra, various technologies are adopted for enhancement, including surface enhancement, semiconductor-based enhancement, etc. Among them, surface enhancement is mostly used, including surface treatment methods such as plasmon enhancement and colloidal particle enhancement. However, surface enhancement requires processing a structure matching the Raman shift, and the enhancement intensity is limited. Summary of the Invention

[0005] The present invention aims at the above problems and provides an optical parametric amplification-enhanced Raman spectroscopy system that can obtain multiple wavelengths, amplify Raman spectra, is applicable to multiple substances, and enables high-fold enhancement of Raman signals.

[0006] The technical solution of the present invention is as follows: An optical parametric amplification-enhanced Raman spectroscopy system includes a laser. After being split by a beam splitter, one path of the laser first passes through a lens and then enters an optical parametric oscillator, and then successively passes through a filter, a lens, a sample, and a filter, and then is combined with the other path of the laser through a beam combiner.

[0007] The combined laser is focused on a sector superlattice 2 through a lens, then passes through an acousto-optic tunable filter, and then the signal is collected by a detector.

[0008] The optical parametric oscillator includes an M1 lens, a sector superlattice 1, an M2 lens, and an M3 lens.

[0009] Among them, the M1 lens, the sector superlattice 1, and the M2 lens are arranged in sequence.

[0010] The M1 lens, the acousto-optic tunable filter, and the M3 lens are arranged in sequence.

[0011] The filter is a long-pass filter.

[0012] The acousto-optic tunable filter includes AOTF1 and AOTF2. Among them, AOTF1 operates in the near-infrared band, and AOTF2 operates in the mid-infrared band.

[0013] AOTF1 is connected between the M1 lens and the M3 lens.

[0014] AOTF2 is connected between the sector superlattice 2 and the detector.

[0015] The periods of the sector superlattice 1 and the sector superlattice 2 are the same.

[0016] The sector superlattice 1 and the sector superlattice 2 are made of lithium niobate material.

[0017] The gain G of optical parametric amplification is:

[0018]

[0019] Among them,

[0020] In the formula, Δk is the phase mismatch, sinh is the hyperbolic sine function, c is the speed of light.

[0021] l c is the crystal length, d eff is the effective nonlinear coefficient, I p (0) is the incident pump light power density, ε0 is the vacuum permittivity, λ s and λ i are the wavelengths of the signal light and the idler light respectively, n s 、n i 、n p are the refractive indices of the signal light, the idler light, and the pump light respectively.

[0022] In the operation of the present invention, the sector superlattice has a sector-shaped polarization period, and the period can be translated according to the central wavelength of the Raman spectrum. The temperature of the sector superlattice is kept stable by temperature control, and the period is changed by moving the displacement stage. Therefore, the wavelength of the excitation light can be changed, and according to the wavelength of the Raman spectrum, the amplification wavelength of the OPA can also be changed. The present invention can flexibly change the excitation wavelength according to the sample and amplify the Raman spectrum.

[0023] The present invention enhances the Raman spectrum through an optical parametric amplifier to obtain higher detection sensitivity. Brief Description of the Drawings

[0024] Figure 1 is a block diagram of the principle of the present invention;

[0025] Figure 2 is a schematic structural diagram of the sector superlattice in the present invention,

[0026] Figure 3 is a schematic diagram of the wavelength corresponding to the period of the sector superlattice,

[0027] Figure 4 is a Raman spectrum diagram of the benzoic acid solution. Detailed Description of the Invention

[0028] The detailed description further explains and illustrates the technical solutions recorded in the claims and the invention content in combination with the drawings of the specification. Note: Explanation needs to be made with reference to the drawings.

[0029] As Figures 1-3 shown, the present invention provides a Raman spectroscopy system with optical parametric amplification enhancement. The 532nm laser emits a laser with a central wavelength of 532nm, which is a pulsed single crystal laser with a pulse length of 5ns - 500ns and a repetition frequency of 1Hz - 10KHz.

[0030] After the laser is split by a beam splitter, 50% of the power enters the sector superlattice 1 and 50% of the power enters the sector superlattice 2.

[0031] The 532nm laser is focused by a lens and enters an optical parametric oscillator (OPO) composed of M1, the sector superlattice 1, M2, and M3. Among them, the M1 and M3 lenses are highly transmissive to 532nm, highly reflective to 600nm - 1000nm, and highly transmissive to 1100nm - 5000nm; the M2 lens is highly transmissive to 532nm, has a reflectivity of 5% - 30% to 600 - 1000nm, and is highly transmissive to 1100nm - 5000nm.

[0032] The OPO tunes the wavelength using the sector superlattice 1 and outputs wavelengths of 600nm - 1000nm and 1100nm - 5000nm, which are called excitation lights.

[0033] To narrow the output spectrum of the OPO, the present invention uses an acousto - optic tunable filter (AOTF) to select the frequency and narrow the resonant light. The AOTF1 is controlled by a radio frequency signal, and different radio frequency signals can change its diffraction wavelength, thereby achieving the selection and narrowing of different wavelengths.

[0034] The above excitation light is filtered by a filter to remove the 532 nm laser, and the remaining excitation light is focused by a lens and then irradiated on the sample to excite the Raman spectrum. The Raman spectrum is filtered by a filter to remove the excitation light, and then combined with the 532 nm laser by a beam combiner. The combined laser is focused by a lens on the sector superlattice 2, and the Raman spectrum is amplified by the optical parametric amplification effect (OPA), and then the 532 nm laser is filtered by AOTF2, and the signal is collected by a detector.

[0035] The filter is a long-pass filter, which allows the Raman spectrum to pass through, while the laser that excites the Raman spectrum is absorbed or reflected.

[0036] The above AOTF is controlled by a radio frequency signal, performs wavelength scanning in the Raman signal wavelength range, and the diffracted Raman signal is detected by a detector.

[0037] The AOTF in the present invention uses a tellurium oxide (TeO₂) crystal and can operate in the near-infrared and mid-infrared bands. Among them, AOTF1 operates in the near-infrared band and AOTF2 operates in the mid-infrared band.

[0038] The acousto-optic tunable filter includes AOTF1 and AOTF2, where AOTF1 operates in the near-infrared band and AOTF2 operates in the mid-infrared band.

[0039] Specifically, the above sector superlattices 1 and 2 are as Figure 2 shown. The dark part of the superlattice represents the positive domain, and the light part represents the negative domain. The sum of the lengths of the positive and negative domains is the period length. The material of the above superlattice is a ferroelectric crystal, such as lithium niobate, lithium tantalate, potassium titanyl phosphate, etc. The above positive and negative domains are realized by the room-temperature voltage inversion technique. The smaller period of the sector superlattice is Λ1, and the larger period is Λ2. The width of the superlattice is W, and the distance from the laser incident position to one side of the large period is H, which can be changed by moving the displacement platform.

[0040] According to the above geometric relationship, the superlattice period Λ passed by the laser is:

[0041]

[0042] Therefore, the period can be determined according to the phase matching of the optical parametric process.

[0043] For the sector superlattice 1, the pump light is 532 nm, so the relationship between the output laser wavelength λ s and the superlattice period Λ satisfies:

[0044]

[0045] In the formula, λ 532 is 532 nm, and n 532is the refractive index of lithium niobate at 532 nm; λ s is the signal light wavelength of the OPO, n s is the refractive index of the signal light wavelength; λ i is the idler light wavelength of the OPO, n i is the refractive index of the idler light wavelength.

[0046] In addition, the wavelength should also satisfy the following energy conservation:

[0047]

[0048] Therefore, for a given Λ, λ s and λ i .

[0049] According to the above relationship, the output wavelengths λ s are 600 nm - 1000 nm and λ i are 1100 nm - 5000 nm, corresponding to Λ being 7 μm - 12 μm. Therefore, Λ1 of the sector superlattice is 7λm, and Λ2 is 12 μm.

[0050] Since the pump light of the sector superlattice 2 is also 532 nm, and the wavelengths of the Raman spectra to be amplified are close to the above λ s and λ i , therefore, the periods of the two sector superlattices are the same.

[0051] The gain G of the above optical parametric amplification is:

[0052]

[0053] Here,

[0054] Δk is the phase mismatch, sinh is the hyperbolic sine function, c is the speed of light,

[0055] l c is the crystal length, d eff is the effective nonlinear coefficient, I p (0) is the incident pump light power density, ε0 is the vacuum permittivity, λ s and λ i are the wavelengths of the signal light and the idler light respectively, n s , n i , n p are the refractive indices of the signal light, the idler light, and the pump light respectively.

[0056] Generally speaking, the gain of optical parametric amplification can reach 10 3 , and even through multi-stage optical parametric amplification, it can reach 10 9 .

[0057] In the present invention, a Raman spectrum is enhanced by an optical parametric amplifier to obtain higher detection sensitivity.

[0058] The present invention will be described below through specific examples.

[0059] The pulse length of the 532n laser of the present invention is 5 ns, the repetition frequency is 10 Hz, and the pulse energy is 100 μJ. This laser obtains single longitudinal mode laser through seed injection technology. The above-mentioned 532 nm laser is divided into two beams by a 50%-50% beam splitter, one of which enters the OPO and the other enters the OPA.

[0060] The sector superlattice in the OPO is moved to obtain an excitation light of 700 nm. The 532 nm laser is filtered out by a filter, and then focused on the sample through a lens.

[0061] The above sample is a benzoic acid solution, which is contained in a glass container. Raman spectra with wavelengths greater than 700 nm are generated by excitation with the excitation light. Then, it passes through a long-pass filter with a cut-off wavelength of 700 nm. The Raman signal spectrum after passing through the filter is as Figure 4 shown.

[0062] The above-mentioned sector superlattice selects lithium niobate material. This lithium niobate is cut and polished into a crystal with a thickness of 1 mm, a length of 50 mm, and a width of 10 mm. The sector superlattice is polarized by the room-temperature electric field polarization method, Λ1 = 7 μm, Λ2 = 12 μm. The refractive indices of each wavelength are obtained according to the Sellmeier equation of lithium niobate, and the period Λ = 8.88 μm is calculated. Therefore, the crystal is moved to a position of H = 3.76 mm through a displacement platform.

[0063] The Raman laser is turned on to output laser to excite the Raman signal spectrum. The pump laser (i.e., the 532 nm laser) is turned on to output pump light synchronized with the output pulse of the Raman laser. When the peak power density of the pump laser pulse reaches I0 = 10 MW / cm 2 ², the gain G = 3.4E5, and the Raman spectrum signal increases by 340,000 times. Therefore, when the concentration of the benzoic acid solution is very small, the amplified Raman spectrum is still strong enough to be detected by the spectrometer, and the sensitivity is improved.

[0064] The above-described embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although specific embodiments are described in detail herein, those skilled in the art can still modify them or replace some technical features in an equivalent manner, and these changes do not depart from the core idea and protection scope embodied in the embodiments of the present invention.

Claims

1. An optical parametric amplification enhanced Raman spectroscopy system, characterized in that: It includes a laser. After the laser is split by a beam splitter, one path of the laser first passes through a lens and then enters an optical parametric oscillator, and then passes through a filter, a lens, a sample and a filter in sequence, and then is combined with another path of the laser through a beam combiner; The combined laser beam is focused on the fan-shaped superlattice 2 by a lens, then passes through an acousto-optic tunable filter, and then the signal is collected by a detector.

2. The optical parametric amplification enhanced Raman spectroscopy system according to claim 1, characterized in that: The optical parametric oscillator includes an M1 lens, a fan-shaped superlattice 1, an M2 lens and an M3 lens. Among them, the M1 lens, the fan-shaped superlattice 1 and the M2 lens are arranged in sequence. The M1 lens, the acousto-optic tunable filter and the M3 lens are arranged in sequence.

3. The optical parametric amplification enhanced Raman spectroscopy system according to claim 1, characterized in that: The filter is a long wave pass filter.

4. The optical parametric amplification enhanced Raman spectroscopy system according to claim 2, characterized in that: The acousto-optic tunable filter comprises AOTF1 and AOTF2, wherein AOTF1 operates in the near-infrared band and AOTF2 operates in the mid-infrared band. AOTF1 is connected between the M1 lens and the M3 lens. AOTF2 is connected between the fan-shaped superlattice 2 and the detector.

5. The optical parametric amplification enhanced Raman spectroscopy system according to claim 1, characterized in that: The periods of the fan-shaped superlattice 1 and the fan-shaped superlattice 2 are the same.

6. The optical parametric amplification enhanced Raman spectroscopy system according to claim 1, characterized in that: The fan-shaped superlattice 1 and the fan-shaped superlattice 2 are made of lithium niobate material.

7. The optical parametric amplification enhanced Raman spectroscopy system according to claim 1, characterized in that: The gain G of optical parametric amplifier is: in, Where Δk is the phase mismatch, sinh is the hyperbolic sine function, c is the speed of light, l c is the crystal length, d eff is the effective nonlinear coefficient, I p (0) is the incident pump light power density, ε0 ​​is the vacuum dielectric constant, λ s and λ i are the wavelengths of the signal light and the idler light, n s 、n i 、n p are the refractive indices of the signal light, idler light and pump light, respectively.

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