Tunable Diode Laser Raman Spectroscopy with Passive Filtering
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Solution Overview
Problem
Conventional Raman spectroscopy systems are expensive, complex, and not suitable for small, compact, and robust arrangements due to the need for high-resolution gratings and multi-channel detectors, which are impaired by high background noise from fluorescence and scattering, especially in fast measurement scenarios without sample preparation.
Innovation Solution
A method using a directly frequency-modulated and narrow-band tunable diode laser to excite samples with multiple wavelengths, combined with wavelength-selective passive filters and single-channel detectors, allowing for the recording of Raman signals without the need for additional spectrometers, enabling cost-effective and compact Raman spectroscopy setups.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional spectrometers with high-resolution gratings and multi-channel detectors are used, then spectral resolution and light sensitivity are improved, but device complexity and cost increase significantly
Solution Approach 1:
The patent extracts the spectral filtering function from the conventional spectrometer and implements it using separate tunable bandpass filters. This separates the excitation wavelength selection from the detection function, allowing the use of simpler single-channel detectors while maintaining spectral resolution through the tunable filters.
Solution Approach 2:
The patent uses multiple bandpass filters with different central wavelengths to selectively transmit different Raman-shifted wavelengths. Each filter acts as a spectral copy selector, allowing the single-channel detector to measure specific spectral components sequentially, replacing the need for complex multi-channel spectral detection.
2Measurement precision
If conventional spectrometers with multi-channel detectors are used, then Raman signal detection capability is improved, but the system becomes expensive and unsuitable for compact arrangements
Solution Approach 1:
The patent extracts the wavelength selection function from the detector system and places it in the optical path using tunable bandpass filters. This allows the use of simple single-channel detectors while maintaining the ability to selectively detect specific Raman wavelengths, eliminating the need for complex multi-channel detector systems.
Solution Approach 2:
The patent introduces tunable bandpass filters as intermediary components between the sample and the detector. These filters selectively transmit desired Raman wavelengths while blocking other wavelengths, enabling simple single-channel detectors to achieve the spectral selectivity that would otherwise require complex multi-channel detector systems.
3Productivity
If measurement time is reduced to less than 1 second for fast analysis, then productivity is improved, but background noise from fluorescence and scattering increases measurement error
Solution Approach 1:
The patent uses periodic modulation of the excitation laser frequency combined with synchronized detection. The laser frequency is modulated to sweep through the excitation wavelength range, and the detector is synchronized to measure at specific phases of this modulation, enabling fast spectral acquisition while maintaining signal-to-background ratio through coherent detection.
Solution Approach 2:
The patent employs feedback-based frequency modulation of the excitation laser, where the laser frequency is actively controlled and adjusted based on feedback signals. This allows precise tracking of resonance conditions and optimization of the excitation wavelength to maximize Raman signal while minimizing fluorescence background, even during fast measurements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for the generation and detection of Raman spectra using inexpensive components, suitable for small, compact, and robust arrangements, effectively reducing background noise and improving measurement accuracy and speed by selectively filtering excitation radiation scattered by the sample.
Implementation Method 1
a directly frequency-modulated and narrow-band tunable diode laser is tuned to excite a sample
Implementation Method 2
the Raman signal of the sample is transmitted via at least one narrow-band passive Filter element
Implementation Method 3
the Raman signal of the sample is transmitted via at least one narrow-band passive Filter element, which is transparent to at least one excitation wavelength Raman-shifted by the sample
Data Source
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AI summary
The method comprises radiating excitation radiation (12, R1, R2) onto a sample (20) to be examined, wherein the sample (20) to be examined is irradiated at least with first excitation radiation (R1) of a first excitation wavelength (λ1) and second excitation radiation (R2) of a second excitation wavelength (λ2), wherein at least the first excitation wavelength (λ1) differs from the second excitation wavelength (λ2). Furthermore, wavelength-selective filtering of the first excitation radiation (R1') scattered by the sample (20) is carried out by means of a passive filter element (30), wherein a transmitted filter wavelength (λF) of the filter element (30) differs from at least the first excitation wavelength (λ1) and the second excitation wavelength (λ2), and wherein a first intensity (I1) is determined from the filtered first excitation radiation (R1") scattered by the sample (20) by means of a detector (40) assigned to the filter wavelength (λF). In addition, wavelength-selective filtering of the second excitation radiation (R2') scattered by the sample (20) is carried out by means of the filter element (30), wherein a second intensity (l2) is determined from the filtered second excitation radiation (R2) scattered by the sample (20) by means of the detector (40) assigned to the filter wavelength (λF).