High-flux wide-spectrum microscopic diffuse reflection illumination system and light path conduction method thereof

Abstract

The invention discloses a high-flux wide-spectrum microscopic diffuse reflection illumination system, which comprises a multiband LED (Light Emitting Diode) light emitting module, an aspheric collimating lens group, a beam combining optical array, an achromatic lens and an output multimode optical fiber, and is characterized in that the multiband LED light emitting module comprises at least three high-power LED units with complementary central wavelengths; the aspheric collimating lens group converts divergent light beams of the LED unit into collimated light beams, the beam combining optical array realizes spatial coaxiality of all the collimated light beams through the dichroscope and combines the collimated light beams into composite full-spectrum collimated light beams, and the achromatic lens focuses the composite full-spectrum collimated light beams on the same focal plane. And the output multimode optical fiber receives the focused composite full-spectrum collimated light beam and serves as a cold light source input end of the microspectrometer. An LED pure cold light source is adopted, infrared heat radiation is avoided, and sample heat damage and catalyst inactivation can be avoided; meanwhile, aspherical collimation, dichroscope beam combination and achromatic coupling are adopted, and high-power output of the wave band of 380-830 nm is achieved.

Description

Technical Field

[0001] This invention relates to the field of spectroscopic detection technology, specifically to a high-throughput, wide-spectrum microscopic diffuse reflectance illumination system and its optical path transmission method, used in microscopic diffuse reflectance spectrometers, and particularly suitable for the characterization of heat-sensitive in-situ powder catalysts. Background Technology

[0002] Microscopic diffuse reflectance spectroscopy is widely used in materials science, catalysis chemistry, and other fields to detect the structure and electronic state information of samples in minute regions (e.g., dd electronic transitions in metal catalysts, surface plasmon resonance (SPR) phenomena, etc.). In existing commercial micro-spectroscopy instruments, the standard illumination source covering the 380nm-1000nm (visible-near infrared) band is usually a tungsten halogen lamp.

[0003] However, tungsten halogen lamps face the following serious technical bottlenecks in practical high-precision in-situ microspectroscopy applications: 1. Uncontrollable thermal radiation damage: The light emission principle of tungsten halogen lamps is accompanied by an extremely high proportion of infrared thermal radiation (thermoluminescence). After focusing in the microscopic optical path, the power density on the sample surface is extremely high, causing localized and severe temperature rises or even burn-out of dark powder samples (such as reduced copper-based catalysts), inducing phase transitions, which seriously interferes with the authenticity of in-situ reaction kinetics and produces "artifacts".

[0004] 2. High light yield leads to low coupling efficiency: Traditional tungsten halogen lamps have a large luminous area, resulting in a severe mismatch between their light yield and the small core diameter of multimode fiber (e.g., 100-300 μm). This causes most of the light energy to be wasted at the fiber coupling end, resulting in a low effective light flux reaching the sample. When facing strongly light-absorbing dark catalysts, the signal-to-noise ratio (SNR) is extremely poor.

[0005] 3. Fixed spectrum and energy depletion at both ends: Halogen lamps exhibit a fixed blackbody radiation curve, with a sharp energy decay in the violet / near-ultraviolet region (380-450 nm), making it extremely difficult to extract spectral information from this area. Furthermore, independent energy compensation based on the characteristic absorption of the sample is not possible.

[0006] 4. Inability to achieve high-frequency modulation: Due to the large thermal inertia of the filament, halogen lamps cannot achieve microsecond-level high-frequency switching modulation, and therefore cannot be used with high-sensitivity spectrometers for real-time accurate dark noise subtraction or to carry out advanced modulation excitation spectroscopy (MES) experiments.

[0007] To address the aforementioned issues, there is an urgent need for a novel lighting optical path architecture that features high throughput, a continuous wide spectrum, perfect cold light source characteristics, and independent modulation of each band. Summary of the Invention

[0008] The purpose of this invention is to provide a high-throughput broadband microscopic diffuse reflection illumination system and its optical path transmission method, so as to overcome the defects of high heat generation, low coupling efficiency and non-modulation in existing tungsten halogen lamps in microscopic diffuse reflection characterization.

[0009] To achieve the above objectives, the present invention provides the following technical solution: a high-throughput broadband microscopic diffuse reflection illumination system, comprising: A multi-band LED light-emitting module, comprising at least three high-power LED units with complementary center wavelengths; An aspherical collimating lens group includes at least three aspherical collimating lenses, each of which is independently disposed in front of the light-emitting surface of an LED unit to convert its divergent beam into a collimated beam. A beam combining optical array includes at least two dichroic mirrors, which are arranged sequentially on the optical path of one of the collimated beams, making the remaining collimated beams spatially coaxial with the collimated beam and merging them into a composite full-spectrum collimated beam; An achromatic lens is placed in the optical path of the composite full-spectrum collimated beam to focus the composite full-spectrum collimated beam onto the same focal plane. The output multimode fiber has its input end face set on the focal plane of the achromatic lens to receive the focused composite full-spectrum collimated beam and serve as the cold light source input end of the micro-spectrometer.

[0010] Preferably, the multi-band LED light-emitting module includes three LED units, namely a short-wavelength first LED unit, a wide-bandwidth second LED unit, and a long-wavelength third LED unit; The aspherical collimating lens group includes three aspherical collimating lenses, which respectively convert the diverging beams of the three LED units into a first collimated beam, a second collimated beam, and a third collimated beam; The beam combining optical array includes two long-pass dichroic mirrors, located at the intersection of the second collimated beam and the third collimated beam, and at the intersection of the first collimated beam and the third collimated beam, respectively.

[0011] Preferably, the two dichroic mirrors are a first dichroic mirror and a second dichroic mirror, which are placed at a 45-degree angle in the optical path of the third collimated beam; wherein, the cutoff wavelength of the first dichroic mirror is set at the junction of the effective emission spectra of the second LED unit and the third LED unit, and the cutoff wavelength of the second dichroic mirror is set at the junction of the effective emission spectra of the second LED unit and the first LED unit. The second collimated beam is incident at a 45-degree angle on the first dichroic mirror and reflected by it, and spatially coaxially merged with the third collimated beam transmitted through the first dichroic mirror to form a mixed beam; the first collimated beam is incident at a 45-degree angle on the second dichroic mirror and reflected by it, and spatially coaxially merged with the mixed beam transmitted through the second dichroic mirror again to finally form the composite full-spectrum collimated beam.

[0012] Preferably, the first LED unit is a violet LED, the second LED unit is a white LED, and the third LED unit is a near-infrared LED.

[0013] Preferably, it is characterized by further comprising: A multi-channel independent driving modulation circuit is electrically connected to the multi-band LED light-emitting module, supporting continuous wave constant current driving and high-frequency pulse width modulation.

[0014] Preferably, the aspherical collimating lens is a short focal length aspherical collimating lens, and the distance between the aspherical collimating lens and the corresponding LED unit is the focal length of the lens. This can correct spherical aberration and convert the diverging beams of each LED unit into collimated beams with the same diameter and parallel height.

[0015] Preferably, the achromatic lens is a doublet achromatic lens formed by bonding crown glass and flint glass, which can eliminate axial chromatic aberration in the 380 nm-830 nm wavelength band.

[0016] Preferably, the output multimode fiber is a large-core multimode fiber with a core diameter greater than or equal to 100 μm, and the effective focusing numerical aperture of the achromatic lens is less than or equal to the numerical aperture of the output multimode fiber.

[0017] This invention also claims protection for a light path conduction method based on the aforementioned lighting system, comprising the following steps: Step S1: Multiple LED units in the multi-band LED light-emitting module are activated synchronously, emitting beams of light in their respective bands. Step S2: The light beams emitted by the LED unit are respectively incident on the corresponding aspherical collimating lenses, and the divergent light beams are corrected into collimated light beams through their collimation effect; Step S3: Use tilted long-pass dichroic mirrors to form a beam combining optical array, and achieve coaxial merging of multi-band light in steps according to wavelength characteristics to form a composite full-spectrum collimated beam. Step S4: The composite full-spectrum collimated beam is incident on the achromatic lens to eliminate axial chromatic aberration in the broadband range and to accurately focus beams of different wavelengths onto the same focal plane. Step S5: The focused composite full-spectrum collimated beam is precisely incident on the output multimode fiber, realizing efficient coupling and transmission of multi-band light, and ultimately providing a high-throughput, wide-spectrum stable light source for microscopic diffuse reflection illumination.

[0018] Compared with the prior art, the beneficial effects of this invention are as follows: 1. Ultra-high optical flux and extremely high energy density: This invention abandons the inefficient broadband beam splitter (50 / 50) and adopts dichroic mirror beam combining, with a beam combining efficiency of over 90%; at the same time, combined with aspherical collimation and achromatic coupling, extremely high optical spread matching is achieved at the fiber end face; according to actual measurements, the absolute optical power coupled out of this invention in the 380-830 nm band is more than 50 times higher than that of commercial tungsten halide fiber light sources of the same level, which greatly improves the signal-to-noise ratio of diffuse reflection signals of dark absorption samples.

[0019] 2. Completely eliminates thermal radiation damage (pure cold light source): This invention emits light through direct electro-optical conversion of LEDs, and the light beam does not contain infrared thermal radiation components, thus completely solving the problem of local overheating and phase change deactivation of in-situ powder catalysts under high-power lighting.

[0020] 3. "Spectral shaping on demand" and broad spectrum smoothness: This invention cleverly utilizes violet LEDs and near-infrared LEDs to compensate for the attenuation at both ends of white LEDs; through independent driving circuits, users can arbitrarily adjust the relative intensity of the three LEDs, thereby "shaping" an ideal smooth spectral background in the 380-830 nm range, or performing targeted energy compensation for strong absorption regions of the sample (such as the dd transition region of copper).

[0021] 4. Support for transient dynamics and precise dark field subtraction: This invention utilizes the microsecond-level response speed of LEDs to perform precise dark current sampling and subtraction by frequently shutting off the light source during the exposure gap of the spectrometer array detector (such as CCD); it also supports rapid phase-sensitive excitation of the light source using modulation excitation spectroscopy (MES) technology. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the light transmission path of the lighting system of the present invention; Figure 2 This is a measured curve comparing the spectral energy distribution of the present invention with that of a traditional commercial tungsten halogen lamp (such as Ocean Optics HL-2000-HP) at the output fiber end. Detailed Implementation

[0023] This invention discloses a high-throughput broadband microscopic diffuse reflection illumination system based on multi-band LED synthesis. Its core optical path, from left to right and bottom to top, specifically includes the following structure and optical transmission process, as detailed in the following documentation. Figure 1 : I. Independent light source array and efficient collimation: The system has three high-power LED chips fixedly installed inside: The first LED unit 101 is a violet / near-ultraviolet LED with a center wavelength of approximately 400 nm.

[0024] The second LED unit 102 is a broadband high color rendering index (CRI>90) white LED, whose main emission peak is concentrated between 450nm-700nm.

[0025] The third LED unit 103 is a near-infrared LED with a center wavelength of approximately 780 nm.

[0026] A short-focal-length aspherical collimating lens (201, 202, 203) is installed directly in front of each LED unit. The distance between the two lenses is usually a few millimeters. The LED unit is located at the focal length of its corresponding aspherical collimating lens.

[0027] LED beams with small luminous areas and large divergence angles are collected and converted into three collimated beams with the same diameter and high parallelism after passing through an aspherical collimating lens, effectively overcoming spherical aberration. These beams are then collimated into three beams: a violet collimated beam, a white collimated beam, and a near-infrared collimated beam.

[0028] II. Lossless Spatial Beam Combining Based on Long-Pass Dichroic Mirrors: This is a crucial step in achieving high throughput. To minimize optical path loss and aberrations, this embodiment employs a long-pass dichroic mirror array with "long-wavelength direct passage and short-wavelength side reflection" for beam combining. The principal optical axis is established based on the propagation direction of the near-infrared collimated beam generated by the third LED unit 103, which has the longest wavelength. 1. A first dichroic mirror 301 is placed at a 45-degree angle on the principal optical axis. This mirror is a long-pass filter with a cutoff wavelength set at approximately 750 nm (LP 750 nm). Near-infrared light (approximately 780 nm) on the principal optical axis can pass through without loss. The collimated white light beam generated by the second LED unit 102 is incident on the mirror at a 45-degree angle from a side perpendicular to the principal optical axis. Since its wavelength (450-700 nm) is smaller than the cutoff wavelength, it is completely reflected by the mirror and thus merges into the principal optical axis, forming a primary mixed beam of "infrared + white light".

[0029] 2. A second dichroic mirror 302 is placed at a 45-degree angle on the principal optical axis behind the first dichroic mirror 301. This mirror is also a long-pass filter with a cutoff wavelength set at approximately 420 nm (LP 420 nm). The primary mixed beam (>450 nm) on the principal optical axis can be transmitted through without loss. The collimated violet beam (approximately 400 nm) generated by the first LED unit 101 is incident on the mirror at a 45-degree angle from a side perpendicular to the principal optical axis. Because its wavelength is smaller than the cutoff wavelength, it is completely reflected and merges into the principal optical axis.

[0030] Thus, relying on two long-pass dichroic mirrors, the three beams of light are perfectly coaxially merged without loss of their individual intensity, forming a composite full-spectrum collimated beam covering 380 nm-830 nm. Since the principal axis light passes through in a straight line, the beam quality degradation caused by multiple reflections is greatly reduced.

[0031] III. Achromatic Coupling and Light Spread Matching: The composite full-spectrum collimated beam continues along the principal optical axis and enters an achromatic lens 401. If a conventional single lens were used, due to material dispersion, the 400 nm violet light and the 780 nm infrared light would focus at two points far apart on the optical axis (axial chromatic aberration), preventing the optical fiber from efficiently receiving wavelengths from both ends simultaneously. The achromatic lens 401, made of crown glass and flint glass with different refractive indices bonded together, can forcibly pull the focal point of a broad spectral band from 380 nm to 830 nm back to a very small depth of focus, ensuring that violet to near-infrared light can be precisely focused onto the same focal plane.

[0032] At the common focal plane of the achromatic lens 401, the input end face of the output multimode fiber 501 is fixed. This input end face receives the focused composite full-spectrum collimated beam and serves as the cold light source input of the micro-spectrometer. To maximize energy transfer (i.e., light spread matching), the selected output multimode fiber is a large-core fiber with a core diameter of 200 μm and a numerical aperture (NA) of 0.22, and the effective focusing numerical aperture of the achromatic lens 401 is required to be slightly less than or equal to 0.22.

[0033] IV. Independent Electrical Control and Spectral Shaping: The system also includes a multi-channel constant current drive circuit (not included in...) Figure 1 As shown in the diagram, each LED is connected to one of three LED units, supporting continuous wave (CW) constant current drive and high-frequency pulse width modulation (PWM). The luminous intensity and switching state of each LED band can be independently and in real-time controlled by software according to experimental requirements. Specifically, it can achieve the following two functions: ① Spectral Shaping: The operator can independently adjust the drive current of the three LED units via the host computer software. For example, when observing... Figure 2When calculating the spectral curve, if insufficient signal is found at 780 nm, the current of the third LED unit 103 can be increased separately to "boost" the local spectral curve, thus completely solving the problem of extremely low energy at both ends of the spectrum of traditional halogen lamps.

[0034] ② High-frequency modulation: The drive circuit supports external TTL trigger signals. When performing Raman or weak diffuse reflection measurements, it can be perfectly synchronized with the exposure time of the spectrometer detector: the LED unit is fully lit when the detector is exposed; the LED unit is turned off instantly when the detector reads data (time < 1μs), which is used to accurately collect the dark noise of the instrument background and greatly improve the final spectral signal-to-noise ratio.

[0035] Figure 2 The graph shows a comparison of the measured spectral energy distribution at the output fiber end of the lighting system of this invention with that of a conventional commercial tungsten halogen lamp (such as Ocean Optics HL-2000-HP). The left curve represents the spectral energy distribution of the system of this invention, and the right curve represents the spectral energy distribution of the conventional tungsten halogen lamp. The test conditions were: fiber diameter 200µm, PTFE white background spectrum, Ocean Optics QE-Pro test, integration time 50ms. The graph shows that: 1. The LED spectrum of this invention is labeled as “50x HL-2000 Intensity”, which means that its intensity is drawn after being magnified 50 times by the tungsten halide lamp spectrum on the right. This indicates that the original absolute optical power of this invention in the 380-830 nm band is much higher than that of commercial tungsten halide fiber light sources of the same level. 2. The LED system of this invention achieves continuous broadband coverage of 380-830 nm by complementing violet light, broadband white light and near-infrared LED, while the spectrum of traditional tungsten halogen lamps has significant energy attenuation in the short-wave region <450 nm and the long-wave region >750 nm, and only has strong radiation in the middle of the visible light range. 3. The LED spectrum of this invention presents a multi-peak structure (violet peak, white light main peak, and near-infrared peak), and the intensity of each peak can be adjusted by independent driving. In contrast, traditional tungsten halogen lamps have a smooth thermal radiation spectrum and cannot be targeted for spectral shaping.

[0036] In summary, this invention, through a systematic optical engineering design of complementary three-color LEDs, aspherical collimation, lossless beam combining with dichroic mirrors, and achromatic coupling, creates an ideal microscopic spectral cold light source in an extremely compact space. This source boasts no thermal damage, a beam combining efficiency of over 90% in the 380-830 nm band, optical power that is more than 50 times higher than that of tungsten halide fiber light sources of the same level, and highly customizable spectral density.

[0037] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-throughput broadband microscopic diffuse reflection illumination system, characterized in that, include: A multi-band LED light-emitting module, comprising at least three high-power LED units with complementary center wavelengths; An aspherical collimating lens group includes at least three aspherical collimating lenses, each of which is independently disposed in front of the light-emitting surface of an LED unit to convert its divergent beam into a collimated beam. A beam combining optical array includes at least two dichroic mirrors, which are arranged sequentially on the optical path of one of the collimated beams, making the remaining collimated beams spatially coaxial with the collimated beam and merging them into a composite full-spectrum collimated beam; An achromatic lens is placed in the optical path of the composite full-spectrum collimated beam to focus the composite full-spectrum collimated beam onto the same focal plane. The output multimode fiber has its input end face set on the focal plane of the achromatic lens to receive the focused composite full-spectrum collimated beam and serve as the cold light source input end of the micro-spectrometer.

2. The lighting system according to claim 1, characterized in that, The multi-band LED light-emitting module includes three LED units: a short-wavelength first LED unit, a wide-band second LED unit, and a long-wavelength third LED unit. The aspherical collimating lens group includes three aspherical collimating lenses, which respectively convert the diverging beams of the three LED units into a first collimated beam, a second collimated beam, and a third collimated beam; The beam combining optical array includes two long-pass dichroic mirrors, located at the intersection of the second collimated beam and the third collimated beam, and at the intersection of the first collimated beam and the third collimated beam, respectively.

3. The lighting system according to claim 2, characterized in that, The two dichroic mirrors are a first dichroic mirror and a second dichroic mirror, which are placed at a 45-degree angle in the optical path of the third collimated beam. The cutoff wavelength of the first dichroic mirror is set at the junction of the effective emission spectra of the second LED unit and the third LED unit, and the cutoff wavelength of the second dichroic mirror is set at the junction of the effective emission spectra of the second LED unit and the first LED unit. The second collimated beam is incident at a 45-degree angle on the first dichroic mirror and reflected by it, and spatially coaxially merged with the third collimated beam transmitted through the first dichroic mirror to form a mixed beam; the first collimated beam is incident at a 45-degree angle on the second dichroic mirror and reflected by it, and spatially coaxially merged with the mixed beam transmitted through the second dichroic mirror again to finally form the composite full-spectrum collimated beam.

4. The lighting system according to claim 2, characterized in that, The first LED unit is a violet LED, the second LED unit is a white LED, and the third LED unit is a near-infrared LED.

5. The lighting system according to claim 1, characterized in that, Also includes: A multi-channel independent driving modulation circuit is electrically connected to the multi-band LED light-emitting module, supporting continuous wave constant current driving and high-frequency pulse width modulation.

6. The lighting system according to claim 1, characterized in that, The aspherical collimating lens is a short focal length aspherical collimating lens. The distance between the aspherical collimating lens and the corresponding LED unit is the focal length of the lens. It can correct spherical aberration and convert the diverging beams of each LED unit into collimated beams with the same diameter and parallel height.

7. The lighting system according to claim 1, characterized in that, The achromatic lens is a doublet achromatic lens formed by bonding crown glass and flint glass, which can eliminate axial chromatic aberration in the 380 nm-830 nm wavelength band.

8. The lighting system according to claim 1, characterized in that, The output multimode fiber is a large-core multimode fiber with a core diameter greater than or equal to 100 μm, and the effective focusing numerical aperture of the achromatic lens is less than or equal to the numerical aperture of the output multimode fiber.

9. A light path transmission method based on the lighting system according to any one of claims 1-8, characterized in that, Includes the following steps: Step S1: Multiple LED units in the multi-band LED light-emitting module are activated synchronously, emitting beams of light in their respective bands. Step S2: The light beams emitted by the LED unit are respectively incident on the corresponding aspherical collimating lenses, and the divergent light beams are corrected into collimated light beams through their collimation effect; Step S3: Use tilted long-pass dichroic mirrors to form a beam combining optical array, and achieve coaxial merging of multi-band light in steps according to wavelength characteristics to form a composite full-spectrum collimated beam. Step S4: The composite full-spectrum collimated beam is incident on the achromatic lens to eliminate axial chromatic aberration in the broadband range and to accurately focus beams of different wavelengths onto the same focal plane. Step S5: The focused composite full-spectrum collimated beam is precisely incident on the output multimode fiber, realizing efficient coupling and transmission of multi-band light, and ultimately providing a high-throughput, wide-spectrum stable light source for microscopic diffuse reflection illumination.

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