Microscopic Raman system with continuously adjustable wavelength based on rotating filter

Abstract

The microscopic Raman system based on the continuous adjustable wavelength of the rotating filter involves the field of resonance Raman. It is equipped with a continuously adjustable wavelength laser, a reflector, a filter, a turntable, an achromatic condensing lens, and a spectrometer; the laser emitted by the continuously adjustable wavelength laser is incident on the reflector and filter on the turntable in turn, and then introduced into the objective lens in the microscope, and is focused on the sample to be tested by the objective lens; the scattered light on the sample to be tested is collected by the objective lens and returned as a collimated beam, and the laser Rayleigh line is filtered out by the filter, and then focused into the spectrometer through the achromatic condensing lens. A special optical path system in which a reflector is integrally linked with the filter is used to achieve the effect of rotating the optical element while the optical path does not move. When the filter rotates, the directions of the two beams of the introduced laser and the derived signal light remain constant. The wavelength tunable long-wave pass filter can be used for both the introduction of laser and the extraction of Raman signal light. The excitation wavelength is continuously adjustable and the light loss is extremely low.

Description

Technical Field

[0001] The invention relates to the field of resonance Raman, in particular to a novel microscopic Raman system with continuously adjustable excitation wavelength based on a rotating filter and continuously adjustable wavelength. Background Art

[0002] Since the probability of Raman scattering from most samples is small and the signal is weak, usually 10% of Rayleigh scattering. -3 -10 -6 Raman spectrometers need to effectively filter out Rayleigh light and reduce stray light background to obtain Raman spectrum detection, so the filter device is a key part of the Raman spectrometer. According to the filtering method, the Raman spectrometers on the market are mainly divided into two categories: one is a single-stage spectrometer using an optical filter; the other is a multi-stage spectrometer using slit or pinhole spatial filtering.

[0003] For the former type of spectrometers that use optical filters, the filter has two important functions in the optical path: one is to attenuate the Rayleigh light intensity in the signal light; the other is to act as a dichroic mirror in the introduction of the laser and the extraction of the Raman signal light. The dichroic mirror function of the filter makes the spectrometer have less light intensity loss for both the laser and Raman signal light when applied to a microscopic Raman system with a 180-degree Raman signal acquisition method, so the detection sensitivity is relatively high. The disadvantage of this type of spectrometer is that the corresponding filter module needs to be replaced when the excitation wavelength is changed, so it is not suitable for situations where the excitation wavelength is continuously adjustable.

[0004] The latter type of multi-stage spectrometer is currently applicable to spectrometer systems with continuously adjustable excitation wavelengths. However, multi-stage spectrometers have the disadvantages of large optical path systems, high costs, and significant signal light loss due to the complexity of the optical path, which leads to low detection sensitivity. In addition, when applied to a microscopic Raman system with a 180-degree Raman signal acquisition method, the introduction of laser light and the extraction of Raman signal light need to be achieved using a semi-transparent and semi-reflective beam splitter, resulting in a loss of half the intensity of the laser and Raman signal light. Therefore, the detection sensitivity is further seriously attenuated.

[0005] Although Semrock Corporation of the United States has developed a filter with continuously tunable cutoff wavelength many years ago, and a domestic research team has also applied this filter to their wavelength tunable system (Liu, X.-L.; Tan, P.-H., Rev. Sci. Instrum. 2017, 88(8), 083114.), the design of this system cannot apply the filter to the laser light path to achieve low-loss laser introduction and Raman signal light extraction. An additional semi-transparent and semi-reflective beamsplitter is used to replace the dichroic mirror, which will inevitably cause the signal light intensity to be attenuated to one-fourth. The reason why this tunable filter cannot be used for the introduction of lasers and the extraction of Raman signal light is that the filter's incident angle needs to be rotated when changing the cutoff wavelength, causing the reflection direction of the laser on the filter to change accordingly. The Raman microscope requires that the direction and position of the laser beam are constant along the optical axis. Therefore, the traditional filter-type Raman microscope cannot use a tunable filter that needs to be rotated to obtain a function suitable for continuously adjustable excitation wavelength. Summary of the invention

[0006] The purpose of the present invention is to address the above-mentioned problems existing in the prior art and to provide a unique optical path system that uses a reflector and a filter in an integrated manner, so that when the filter angle is rotated to change the filtered wavelength, the direction and position of the laser beam and the scattered signal beam remain unchanged, thereby obtaining a microscopic Raman system based on a rotating filter with continuously adjustable wavelength and extremely low light loss, which is suitable for continuously adjustable excitation wavelength.

[0007] The present invention is provided with:

[0008] A wavelength continuously tunable laser for outputting monochromatic lasers of different wavelengths;

[0009] A reflector is used to link the filter so that the original direction and position of the light path will not be changed when the filter rotates;

[0010] A filter, which is a wavelength-tunable long-wave pass filter. By rotating the filter to change the angle between it and the incident light, the laser beams with different wavelengths can be cut off.

[0011] A turntable, used to fix the reflector and the filter vertically on the turntable at a fixed angle and rotate them together. When the intersection line of the plane where the reflector and the filter are located coincides with the rotation axis of the turntable, the light whose incident surface is perpendicular to the rotation axis will have a constant output light;

[0012] An achromatic condenser lens is used to focus the Raman scattered light and introduce it into the spectrometer.

[0013] A spectrometer is used to record the Raman scattered light and convert it into electronic digital signals to obtain a Raman spectrum.

[0014] The laser emitted by the wavelength continuously adjustable laser is incident on the reflector and filter on the turntable in turn, and then introduced into the objective lens in the microscope, and is focused onto the sample to be tested by the objective lens; the scattered light on the sample to be tested is collected by the objective lens and returned as a collimated beam, and the laser Rayleigh line is filtered out by the filter, and then focused into the spectrometer by the achromatic condenser lens.

[0015] The achromatic condenser lens can be replaced by a concave reflecting mirror.

[0016] The reflector and the filter are fixed on a turntable and rotate integrally, and the rotation axis of the turntable coincides with the intersection line of two planes where the reflector and the filter are located.

[0017] The rotating axis of the rotating table is perpendicular to the incident surfaces of the laser beam on the reflecting mirror and the filter.

[0018] The integrated rotation means that the direction and position of the laser beam reflected by the filter do not change when the turntable is rotated.

[0019] The cut-off wavelength of the filter is slightly larger than the excitation wavelength.

[0020] The wavelength is continuously adjustable. You can arbitrarily select a Raman test excitation wavelength output by the wavelength continuously adjustable laser, select a filter with a cutoff wavelength adjustable range covering the wavelength, and rotate the turntable to make the filter cutoff wavelength slightly larger than the excitation wavelength for Raman testing.

[0021] The present invention has the following outstanding advantages and technical effects:

[0022] 1. The present invention utilizes a special optical path system in which a reflector follows the filter in an integrated manner to achieve the effect of rotating the optical element while the optical path remains stationary. When the filter rotates, the directions of the two beams of the introduced laser and the derived signal light remain constant, thereby realizing a wavelength-tunable Raman system with extremely low Raman signal light flux loss. The wavelength-tunable long-wave filter can be used for both the introduction of laser light and the extraction of Raman signal light, and the optical path remains stationary when the filter is rotated and adjusted, thereby obtaining a microscopic Raman optical path system suitable for continuously adjustable excitation wavelength and extremely low light loss.

[0023] 2. The optical path structure of the present invention enables the filter to play the role of a dichroic mirror in the introduction of laser light, so that in a microscopic Raman system with a 180-degree Raman signal collection mode, there is no need to add an additional beam splitter to achieve the introduction of laser light and the extraction of signals, thereby avoiding the average loss of the laser and Raman signal light intensities by half. Therefore, under the conditions of the same level of laser power and spectrometer parameters, the Raman spectrometer system of the present invention can increase the detection sensitivity by 4 times. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The schematic diagram of the structure of a microscopic Raman system with continuously adjustable wavelength based on a rotating filter according to an embodiment of the present invention.

[0025] Figure 2 for Figure 1 Equivalent optical path diagram. DETAILED DESCRIPTION

[0026] The following examples will further illustrate the present invention in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0027] See also Figure 1 , in the figure, the mark 1 is a wavelength continuously tunable laser, 2 is a turntable, 3 is a reflector, 4 is a wavelength tunable long-wave filter, 5 is a microscope, 6 is an objective lens, 7 is an achromatic condenser lens, and 8 is a spectrometer;

[0028] The embodiment of the present invention is provided with:

[0029] A wavelength continuously tunable laser 1 outputs monochromatic lasers of different wavelengths.

[0030] A turntable 2 is provided, on which the reflector and the filter are fixed vertically at a fixed angle and rotated together. It can be proved by geometry that when the intersection line of the planes where the two are located coincides with the axis of rotation of the turntable, the light whose incident surface is perpendicular to the axis of rotation will have a constant output light.

[0031] A reflector 3 is linked to the filter, and when the filter rotates, the original direction and position of the light path are not changed.

[0032] A wavelength-tunable long-wave pass filter 4 is used to cut off the transmission of lasers of different wavelengths by rotating the filter to change the angle between the filter and the incident light.

[0033] An achromatic condenser lens 7 is used to focus the Raman scattered light and introduce it into the spectrometer.

[0034] A spectrometer 8 records the Raman scattered light and converts it into electronic digital signals to obtain a Raman spectrum.

[0035] The reflector 3 and the filter 4 are fixed vertically on the turntable 2 at a fixed angle, and ensure that the intersection line of the planes where the reflector 3 and the filter 4 are located coincides with the rotation axis of the turntable 2. The laser beam emitted by the wavelength continuously adjustable laser 1 is reflected by the reflector 3 and incident on the filter 4. The turntable is rotated appropriately to make the filter cutoff wavelength slightly larger than the laser wavelength, so that the laser is reflected and introduced into the objective lens 6 in the microscope 5, and is focused on the sample to be measured through the objective lens 6. The scattered light of the sample is collected by the objective lens 6 and becomes a collimated beam. After filtering out the laser Rayleigh line in the scattered light through the filter 4, it is focused into the spectrometer 8 through the achromatic condenser lens 7, and outputs the Raman spectrum data through photoelectric conversion.

[0036] See also Figure 2 When the excitation wavelength output by the laser 1 is changed, the turntable 2 is rotated accordingly so that the cutoff wavelength of the filter 4 is slightly larger than the excitation wavelength. Since the position and direction of the laser reflected by the filter 4 remain unchanged during the rotation process, the position of the light spot focused on the sample remains unchanged, thereby realizing the Raman detection of the excitation wavelength of the sample to be tested being continuously adjustable.

Claims

1. A microscopic Raman system based on a rotating filter with continuously adjustable wavelength, characterized by Features: A wavelength continuously tunable laser for outputting monochromatic lasers of different wavelengths; A reflector is used to link the filter so that the original direction and position of the light path will not be changed when the filter rotates; A filter, which is a wavelength-tunable long-wave pass filter. By rotating the filter to change the angle between it and the incident light, the laser beams with different wavelengths can be cut off. A turntable, used to fix the reflector and the filter vertically on the turntable at a fixed angle and rotate them together. When the intersection line of the plane where the reflector and the filter are located coincides with the rotation axis of the turntable, the light whose incident surface is perpendicular to the rotation axis will have a constant output light; an achromatic condenser lens to focus the Raman scattered light and introduce it into the spectrometer; A spectrometer is used to record the Raman scattered light and convert it into electronic digital signals to obtain a Raman spectrum.

2. The Raman microscope system with continuously adjustable wavelength based on rotating filter as claimed in claim 1, characterized in that The laser emitted by the wavelength continuously adjustable laser is incident on the reflector and filter on the turntable in sequence, and then introduced into the objective lens in the microscope, and is focused onto the sample to be tested by the objective lens; the scattered light on the sample to be tested is collected by the objective lens and returned as a collimated light beam, and the laser Rayleigh line is filtered out by the filter, and then focused into the spectrometer by the achromatic condenser lens.

3. The Raman microscope system with continuously adjustable wavelength based on rotating filter as claimed in claim 1, characterized in that The achromatic condenser lens is replaced by a concave mirror.

4. The Raman microscope system with continuously adjustable wavelength based on rotating filter as claimed in claim 1, characterized in that The reflector and the filter are fixed on a turntable and rotate integrally, and the rotation axis of the turntable coincides with the intersection line of two planes where the reflector and the filter are located.

5. The Raman microscope system with continuously adjustable wavelength based on rotating filter as claimed in claim 1, characterized in that The rotating axis of the rotating table is perpendicular to the incident surfaces of the laser beam on the reflecting mirror and the filter.

6. The Raman microscope system with continuously adjustable wavelength based on rotating filter as claimed in claim 4, characterized in that The integrated rotation means that the direction and position of the laser beam reflected by the filter do not change when the turntable is rotated.

7. The Raman microscope system with continuously adjustable wavelength based on rotating filter as claimed in claim 1, characterized in that The cut-off wavelength of the filter is greater than the excitation wavelength.

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