A nonlinear optical coupling device and system thereof

Abstract

The present invention provides a nonlinear optical coupling device and system, belonging to the field of material information characterization technology. This device utilizes the correlation between the Raman optical path and the nonlinear optical path to simultaneously complete the acquisition of Raman single spectrum and Raman imaging, as well as nonlinear optical data such as second harmonic and third harmonic single spectrum and imaging on the same sample. This results in a compact optical path structure, stable optical path, good adjustability, easy operation, and strong practicality. It has broad application prospects in the field of optical characterization.

Description

Technical Field

[0001] The present invention relates to the technical field of material information characterization, and in particular to a nonlinear optical coupling device and a system thereof. Background Art

[0002] Structural information about crystalline materials, such as their crystal phase, lattice orientation, stacking pattern, and defects, is crucial for studying their physical properties and exploring their applications. This information can be obtained through electron microscopy techniques such as scanning electron microscopy, transmission electron microscopy, and scanning tunneling electron microscopy. However, electron microscopy has stringent requirements for sample preparation, testing environment, sample crystal state, and type, and the high electron beam energy can easily cause irreversible damage to the sample, limiting the scope of testing. Optical microscopy, which has no strict requirements for sample morphology or testing environment and offers advantages such as simplicity, low testing cost, and non-destructive testing, has become an indispensable tool for characterizing material structure. Second harmonic generation (SHG) is a recently developed optical microscopy technique that boasts the high spatial resolution unique to nonlinear optics and can detect lattice orientation, grain boundaries, and stacking. Furthermore, SHG generation does not rely on absorption processes; there is no energy loss when photons interact with the material, thus preventing damage to the material structure during testing. SHG also requires no special material treatment, simplifying the experimental process and avoiding the effects of exogenous treatments on the material itself. Due to the above characteristics, second harmonic generation has shown attractive application prospects in the fields of materials, biology, medicine, etc. in recent years.

[0003] Existing optical coupling often has a complex structure and suffers from problems such as insufficient optical path stability and poor adjustability. Summary of the Invention

[0004] In view of the problems existing in the prior art, the present invention aims to design a coupling device that is adaptable and stable to Raman spectroscopy. The coupling device can introduce a free light path into the confocal Raman light path and can simplify, stabilize and flexibly adjust the light path.

[0005] The present invention provides a nonlinear optical coupling device, which includes a coupler body, a coupling cavity, a position rod and a reflector assembly;

[0006] The reflector assembly includes a beam confinement unit, a reflector and a dichroic mirror; the in-position rod extends into the coupling cavity through the coupler body and is connected to the dichroic mirror in the coupling cavity;

[0007] The coupler body is arranged on the laser incident light path of the Raman optical system, the dichroic mirror is located in the coupling cavity; the in-position rod is connected to the dichroic mirror; the reflector is located directly above the beam confinement unit at a 45° angle, and reflects the incident light passing through the beam confinement unit to the dichroic mirror in the coupling cavity; the nonlinear light is a second harmonic or a third harmonic.

[0008] Preferably, an adjustment knob is provided on the reflector.

[0009] Preferably, the dichroic mirror is a short-wave pass dichroic mirror.

[0010] Preferably, the dichroic mirror reflects the pump light source and transmits the nonlinear light.

[0011] Preferably, the beam confinement unit includes an upper disc and a lower disc; through holes are set in the center of the upper disc and the lower disc, and the two through holes are concentrically arranged in the vertical direction; the upper disc and the lower disc are slidably connected by a connecting rod, and the distance between the upper disc and the lower disc is adjustable.

[0012] Preferably, the in-position rod is arranged on the side of the coupler body, the end of the in-position rod extends out of the coupler body, and the other end of the in-position rod is connected to the dichroic mirror through a bracket. The in-position rod adjusts the position of the dichroic mirror in the coupling cavity by telescoping, thereby controlling whether the dichroic mirror is on the optical path of the Raman optical path system.

[0013] Preferably, the nonlinear optical coupling device further comprises an external angle adjustment device, and the direction of the dichroic mirror is adjusted by the external angle adjustment device.

[0014] The present invention also provides a confocal Raman nonlinear optical coupling system, which includes a pump laser system, a Raman optical system and the above-mentioned nonlinear optical coupling unit;

[0015] The output direction of the pump laser system is provided with a laser attenuation unit, a total reflection unit, a beam lifting unit, and a nonlinear optical coupling unit in sequence along the optical path.

[0016] Preferably, the pump laser system outputs a modulated ultrafast femtosecond laser that enters the nonlinear optical coupling device through a return optical path, and enters the Raman optical system through the laser attenuation unit, the total reflection unit, the beam lifting unit, and the nonlinear optical coupling device. The nonlinear optical coupling of the confocal Raman optical system is achieved through the adjustable setting of the reflector assembly, and the direction of the dichroic mirror and the setting of the beam confinement unit are adjusted in conjunction to improve the collection efficiency of the second harmonic generation signal.

[0017] Compared with the existing technical solutions, the present invention has at least the following beneficial effects:

[0018] 1) The present invention introduces femtosecond laser into the confocal scanning Raman spectrometer by designing a nonlinear optical coupling device, thereby achieving the coupled composite use of Raman and nonlinear optics and improving the efficiency of material characterization;

[0019] 2) The present invention adjusts the focus position of the pump light source to be the same as the focus position of the Raman laser through an adjustment device, and adjusts the collection aperture of the Raman laser to maximize the modulation of the nonlinear optical signal;

[0020] 3) The present invention utilizes the relationship between the Raman optical path and the nonlinear optical path to simultaneously complete the acquisition process of Raman single spectrum, Raman imaging, and nonlinear optical such as second harmonic and third harmonic single spectrum and imaging on the same sample, making the optical path structure compact, stable, and adjustable, easy to operate, and highly practical. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 1 is a schematic structural diagram of a nonlinear optical coupling unit according to a preferred embodiment of the present invention;

[0022] Figure 2 FIG. 1 is a structural diagram of a beam confinement unit according to a preferred embodiment of the present invention.

[0023] Figure numerals: 1. Coupler body, 2. Coupling cavity, 3. In-position rod, 4. Reflector I, 5. Beam confinement unit, 6. Disc, 7. Through hole, 8. External angle adjustment device, 9. Dichroic mirror, 10. Adjustment knob.

[0024] The present invention is further described in detail below. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims. Specific embodiments

[0025] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific implementation methods.

[0026] The confocal scanning Raman spectrometer can perform Raman and fluorescence characterization on crystalline materials, detecting information such as the material's crystal phase, crystallinity, thickness, and morphology. Since the detection device for second harmonic generation is basically the same as the detection device of the confocal scanning Raman spectrometer, the two can be used in combination to obtain more material crystal structure information (lattice orientation, grain boundaries, and stacking) from different complementary aspects, expanding the characterization function of the Raman system. By equipping the existing confocal scanning Raman optical microscope system with a second harmonic test optical path, SHG single spectrum testing and regional imaging can be achieved on the basis of Raman and fluorescence characterization, which greatly promotes a more comprehensive understanding and grasp of the material's lattice vibration, lattice orientation, symmetry, stacking, grain boundaries and other properties.

[0027] As an indispensable tool for characterizing optoelectronic functional materials, Raman spectroscopy offers non-destructive characterization, minimal testing requirements, and the ability to capture the fingerprint of specific systems. Therefore, it can be used to study phonon vibrations, phase composition, stress and strain, defect density, anisotropy, and other properties. Compared to large instruments like neutron scattering, Raman spectroscopy boasts a simple optical path and instrumentation, making it easy to combine with other microanalytical testing methods for in situ characterization. This combined characterization allows in situ analysis of the microstructure of optoelectronic functional materials to gain more information about the material structure and lattice orientation, while improving characterization efficiency. Second harmonic generation (SHG) is a recently developed optical microscopy technique with the high spatial resolution unique to nonlinear optics, enabling the examination of lattice orientation, grain boundaries, and stacking within samples. Furthermore, SHG generation does not rely on absorption processes; there is no energy loss when photons interact with the material, thus preventing damage to the optoelectronic material structure during testing. SHG measurements do not require special material preparation, simplifying the experimental process and avoiding the effects of exogenous treatment on the optoelectronic material itself. The present invention combines the Raman spectroscopy system with the nonlinear optical system to achieve one-stop structural characterization of phase composition, lattice orientation, stacking, structural symmetry, etc.

[0028] As an all-optical characterization method, second harmonic optical imaging connected to a confocal scanning Raman spectrometer system is used for material characterization testing. It has no requirements for the material morphology and will not destroy the material structure during the test process. It is an excellent testing method for samples that are difficult to characterize using electron microscopy technology.

[0029] The confocal Raman spectroscopy system of the present invention utilizes lasers of multiple wavelengths, with continuously adjustable laser power within a maximum power range. This system enables observation and analysis of different stages of the same sample. The confocal device not only collects information from the sample surface but also allows observation of the interior of transparent samples, even acquiring three-dimensional information. Furthermore, by employing a polarization measurement system comprised of a 360° rotatable half-wave plate for visible light and a polarization analyzer, the system can identify the vibrational mode of the Raman peak based on the relationship between the Raman intensity and the material's Raman tensor, the incident laser vector, and the scattered light vector. This allows for the determination of material anisotropy and the non-destructive determination of the crystal axis orientation of anisotropic materials.

[0030] When adjusting the optical path, a nonlinear optical coupler is used to connect the pump light source, and the nonlinear optical coupling optical path is adjusted by the in-position rod, so that the pump light adjusts the emission wavelength through the optical parametric oscillator, passes through the laser attenuation unit, the total reflection unit, the beam lifting unit, the nonlinear optical coupling unit, and through optical path calibration, especially through the beam constraint unit and the external angle adjustment device, step-by-step fine-tuning is performed to adjust the pump light source and the Raman laser to the confocal position.

[0031] like Figure 1 FIG. 1 is a schematic diagram of the structure of a nonlinear optical coupling unit according to a preferred embodiment of the present invention. The nonlinear optical coupling unit comprises a coupler body 1, a coupling cavity 2, a positioning rod 3, a reflector assembly, and an external angle adjustment device 8. The reflector assembly comprises a beam confinement unit 5, a reflector 4, and a dichroic mirror 9. The positioning rod extends through the coupler body 1 into the coupling cavity 2 and connects to the dichroic mirror 9 within the coupling cavity 2. The coupler body 1 is positioned in the incident light path of the Raman optical system laser. The dichroic mirror 9 of the reflector assembly is located within the coupling cavity 2, and the direction of the dichroic mirror 9 is adjusted by the external angle adjustment device 8. The positioning rod 3 is connected to the dichroic mirror 9. The reflector 4 is positioned directly above the beam confinement unit 5 at a 45° angle to reflect the incident light passing through the beam confinement unit 5 to the dichroic mirror 9 within the coupling cavity 2. An adjustment knob 10 is provided on the reflector 1.

[0032] like Figure 2 As shown in the figure, it is a schematic diagram of the structure of a beam confinement unit of a preferred embodiment of the present invention; the beam confinement unit includes two upper and lower discs 6, a through hole 7 is set in the center of the upper and lower discs, the upper and lower discs are slidably connected by a connecting rod, and the distance between the discs is adjustable; specifically, the dichroic mirror 9 is a short-wave dichroic mirror.

[0033] Specifically, the dichroic mirror coating is reflective to the pump light source and transmissive to the nonlinear light.

[0034] The nonlinear light is a second harmonic or a third harmonic.

[0035] The upper and lower through holes of the beam confinement unit are concentrically arranged in the vertical direction.

[0036] The disc is provided with an aperture adjustment device, and the aperture adjustment range is 3-5 mm.

[0037] The disc has a certain thickness, ranging from 3 to 10 mm.

[0038] The in-position rod 3 is arranged on the side of the coupler body 1, and the end of the in-position rod 3 extends out of the coupler body 1. The other end of the in-position rod is connected to the dichroic mirror 9 in the coupling cavity 2 through a bracket. The in-position rod 3 adjusts the position of the dichroic mirror 9 in the coupling cavity by telescoping, thereby controlling whether the dichroic mirror 9 is on the optical path of the Raman optical path system.

[0039] The external angle adjustment device 8 adjusts the angle of the dichroic mirror 9 through three adjustment knobs.

[0040] The coupler body 1, the positioning rod 3, the reflector assembly and the external angle adjustment device 8 are respectively connected through brackets or connecting pieces.

[0041] The adjusting end of the adjusting knob 10 is recessed into the coupler body to avoid accidental touch.

[0042] In practice, a lithium yttrium fluoride-LBO ultrafast crystal is used as the laser crystal. The laser is modulated by an optical parametric oscillator (OPO). The output pump light passes through a laser attenuation unit, a total reflection unit, a beam-boosting unit, and a nonlinear optical coupler. Through optical path calibration, particularly through the beam confinement unit and an external angle adjustment device 8, gradual fine-tuning is performed to adjust the pump light source and the Raman laser to a cofocal position. By simultaneously turning on the Raman laser and the pump light path, adjusting the focus of the pump light source to the same position as the Raman laser through an adjustment device, and adjusting the collection aperture of the Raman laser to maximize nonlinear optical signal modulation, the optimal state for Raman and nonlinear optical signal collection is achieved, achieving a pump light output range of 340-1600nm and a nonlinear optical signal collection range of 340-800nm.

[0043] This device utilizes the connection between the Raman optical path and the nonlinear optical path to simultaneously complete the acquisition of Raman single spectrum and Raman imaging, as well as nonlinear optical acquisition such as second harmonic and third harmonic single spectrum and imaging, on the same sample. This results in a compact optical path structure, stable optical path, good adjustability, easy operation, and strong practicality. It has broad application prospects in the field of optical characterization.

[0044] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

[0045] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0046] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A nonlinear optical coupling device, characterized in that: The nonlinear optical coupling device comprises a coupler body, a coupling cavity, a position rod and a reflector assembly; The reflector assembly includes a beam confinement unit, a reflector and a dichroic mirror; the in-position rod extends into the coupling cavity through the coupler body and is connected to the dichroic mirror in the coupling cavity; The beam confinement unit includes an upper disc and a lower disc; through holes are provided in the centers of the upper disc and the lower disc, and the two through holes are concentrically arranged in the vertical direction; the upper disc and the lower disc are slidably connected by a connecting rod, and the distance between the upper disc and the lower disc is adjustable; The coupler body is arranged on the incident light path of the Raman optical system laser, and the dichroic mirror is located in the coupling cavity; the in-position rod is connected to the dichroic mirror; the reflector is located directly above the beam confinement unit at a 45° angle, and reflects the incident light passing through the beam confinement unit to the dichroic mirror in the coupling cavity; The on-position rod is arranged on the side of the coupler body, the end of the on-position rod extends out of the coupler body, and the other end of the on-position rod is connected to the dichroic mirror via a bracket. The on-position rod adjusts the position of the dichroic mirror in the coupling cavity by telescoping, thereby controlling whether the dichroic mirror is on the optical path of the Raman optical path system; The nonlinear light is a second harmonic or a third harmonic.

2. The nonlinear optical coupling device according to claim 1, wherein: An adjusting knob is provided on the reflector.

3. The nonlinear optical coupling device according to claim 1, wherein: The dichroic mirror is a short-wave pass dichroic mirror.

4. The nonlinear optical coupling device according to claim 1, wherein: The dichroic mirror reflects the pump light source and transmits the nonlinear light.

5. The nonlinear optical coupling device according to claim 1, wherein: The nonlinear optical coupling device further comprises an external angle adjustment device, and the direction of the dichroic mirror is adjusted by the external angle adjustment device.

6. A confocal Raman nonlinear optical coupling system, characterized by: The system comprises a pump laser system, a Raman optical system and a nonlinear optical coupling device according to any one of claims 1 to 5; The output direction of the pump laser system is provided with a laser attenuation unit, a total reflection unit, a beam lifting unit, and a nonlinear optical coupling device in sequence along the optical path.

7. The nonlinear optical coupling system according to claim 6, wherein: The pump laser system outputs a modulated ultrafast femtosecond laser which enters the nonlinear optical coupling device through a return optical path, and enters the Raman optical system through the laser attenuation unit, the total reflection unit, the beam lifting unit, and the nonlinear optical coupling device. The nonlinear optical coupling of the confocal Raman optical system is achieved through the adjustable setting of the reflector assembly, and the direction of the dichroic mirror and the setting of the beam confinement unit are adjusted in conjunction to improve the collection efficiency of the second harmonic generation signal.

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