Raman Spectrometer Charge-Shifting CCD Ambient Light Rejection
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Solution Overview
Problem
Raman spectroscopy outside laboratory settings faces challenges due to weak signal susceptibility to ambient light interference, fluorescence, and the need for robust, portable, and cost-effective devices that can handle varying light conditions and sample degradation.
Innovation Solution
A technique using fast optical lock-in detection with charge-shifting operations in a CCD, where charge is shifted between illuminated and non-illuminated areas on the CCD chip to separate Raman and background signals, allowing for kilohertz frequency operation without noise penalty, and utilizing multiple wavelengths to compensate for ambient light and fluorescence variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If ambient light is blocked by physically covering the contact area, then ambient light interference is prevented, but device portability and user-friendliness are compromised
Solution Approach 1:
The patent replaces mechanical light blocking (physical covers) with an optical filtering system using dichroic mirrors and bandpass filters. The system selectively transmits laser wavelengths while blocking ambient light spectrally, eliminating the need for mechanical covers and enabling handheld portability.
Solution Approach 2:
The patent changes the spectral parameters of light detection by using tunable filters and dichroic mirrors that can selectively transmit or block specific wavelength ranges. This allows the system to adapt to different laser wavelengths and block ambient light dynamically without mechanical intervention.
2Object-affected harmful factors
If short-pulsed lasers with gating are used to overcome ambient light, then ambient light interference is reduced, but device complexity and cost increase
Solution Approach 1:
The patent replaces complex temporal gating systems with simpler spectral filtering using dichroic mirrors and bandpass filters. The system achieves ambient light rejection through wavelength-selective optics rather than requiring precise temporal synchronization and gating electronics.
Solution Approach 2:
The patent creates a universal optical filtering system that works with continuous-wave lasers at multiple wavelengths using dichroic mirrors and tunable bandpass filters. This eliminates the need for complex pulsed laser systems and gating electronics while maintaining effectiveness against ambient light.
3Object-affected harmful factors
If UV laser probe light below 300 nm is used, then solar radiation interference is blocked, but sample degradation occurs
Solution Approach 1:
The patent changes the wavelength parameter of the laser probe from UV below 300 nm to visible or near-IR wavelengths (e.g., 405 nm, 488 nm, 532 nm, 633 nm, 785 nm). Combined with spectral filtering, this eliminates both solar interference and sample degradation while maintaining Raman signal detection capability.
4Measurement precision
If longer exposure periods are used to compensate for variable ambient light, then measurement accuracy is improved, but measurement time increases
Solution Approach 1:
The patent performs preliminary spectral characterization of ambient light and stores reference spectra. During measurement, the system rapidly acquires reference and sample spectra and uses pre-computed compensation algorithms to correct for ambient light variations, enabling accurate compensation with minimal exposure time.
Solution Approach 2:
The patent implements a feedback system where the detector continuously monitors ambient light levels and spectral characteristics. The system dynamically adjusts laser power, integration time, and filter selection based on real-time ambient conditions, optimizing measurement speed and accuracy adaptively.
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 method enhances the signal-to-noise ratio of Raman spectral measurements, enabling faster and more accurate chemical characterization of samples under dynamic lighting conditions, with improved reproducibility and reduced data volume and measurement time.
Implementation Method 1
A technique using fast optical lock-in detection with charge-shifting operations in a CCD, where charge is shifted between illuminated and non-illuminated areas on the CCD chip to separate Raman and background signals
Implementation Method 2
Raman spectroscopy is a powerful analytical method which can be used to determine the chemical composition of various samples
Implementation Method 3
Raman spectroscopy of a sample can also be adversely affected by fluorescence of the sample, and in particular by fluorescence excited by the same laser light illumination of the sample as used for the detection of Raman spectral features
Implementation Method 4
collection optics arranged to direct light from the sample to the detection pixels
Implementation Method 5
an analyser arranged to receive from the CCD, after an exposure period, the first and second spectral signals accumulated during the exposure period and to compensate for ambient light in the first and second spectral signals and to determine one or more characteristics of the sample from the compensated spectral signals
Data Source
AI summary
There are disclosed methods and apparatus (10) for measuring Raman spectral features (52) of a sample (12), from which background light of variable intensity is also received, for example due to the incidence of ambient light (14) or due to variable fluorescence. Detection pixels (42) and storage pixels (44) are defined on a CCD device (40). Laser probe light (22) is directed to the sample. In a repeated cycle of first and second intervals, in each first interval background light is received at detection pixels, and in each second interval both background light and scattered laser probe light is received at the detection pixels. The accumulated signal from each of the first and second intervals is retained in the storage pixels during the second and first intervals respectively. In other aspects laser probe light is directed to the sample during both of the first and second intervals, but has a different wavelength in each interval.