Time-Gated Raman Spectral Mapping Apparatus
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Solution Overview
Problem
Current Raman spectroscopy techniques face challenges in effectively suppressing fluorescence emission noise, particularly in pigmented samples, leading to long acquisition times and poor signal-to-noise ratios due to the use of complex systems and expensive detectors.
Innovation Solution
A time-gated Raman spectral mapping apparatus utilizing a pulsed illumination source, spectral filtering with a dispersive element and spatial light modulator, and a single-pixel detector to distinguish Raman scattered radiation from photoluminescence, allowing for simultaneous detection of multiple Raman peaks and reducing acquisition time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If optical gating techniques (Kerr gate or iCCD) are used to suppress fluorescence, then fluorescence suppression and spectral resolution are improved, but acquisition time increases and system complexity increases
Solution Approach 1:
The patent extracts and isolates only the Raman signal photons within a specific time window (e.g., 0-100 ps after laser pulse) using time-gated detection, separating them from the fluorescence background that occurs at later times. This temporal extraction allows fluorescence suppression without requiring complex optical gating systems or long acquisition times.
Solution Approach 2:
The patent employs periodic pulsed laser excitation with repetition rates typically in the MHz range, synchronizing the detection gate with each laser pulse. This periodic action allows rapid sequential measurement of Raman signals at multiple spatial locations, reducing total acquisition time while maintaining effective fluorescence suppression through consistent time-gating.
2Measurement precision
If optical Kerr gating is used to achieve high temporal resolution, then fluorescence suppression is improved, but device complexity increases due to requirement of powerful pulsed laser systems
Solution Approach 1:
The patent replaces complex mechanical/optical gating systems (Kerr gates requiring powerful pulsed lasers) with a simpler time-correlated single photon counting approach using a single-photon detector and electronic timing circuitry. This substitution achieves comparable or superior temporal resolution (picosecond to nanosecond gating windows) with significantly reduced system complexity and lower laser power requirements.
Solution Approach 2:
The patent changes the detection parameter from intensity measurement (continuous wave) to time-resolved single-photon counting, measuring the arrival time of individual photons relative to the laser pulse. This parameter change enables precise temporal gating (e.g., accepting photons within 0-100 ps after pulse) to achieve high temporal resolution and fluorescence suppression without complex optical gating hardware.
3Measurement precision
If time-correlated single photon counting with scanning monochromator is used, then temporal resolution is improved, but productivity decreases due to large number of measurements required for mapping
Solution Approach 1:
The patent merges the temporal resolution capability of time-correlated single photon counting with the spatial mapping capability of confocal microscopy by implementing rapid sequential scanning. The system combines the time-gated detector with a fast scanning mechanism (galvanometer mirrors or piezoelectric stage) to quickly move between spatial locations, accumulating Raman spectra at each point while maintaining temporal gating for fluorescence suppression.
Solution Approach 2:
The patent maintains continuous useful action by keeping the detector in a ready state, continuously monitoring for photons within the gated time window, and rapidly transitioning between measurement points without resetting the detection system. The scanning mechanism continuously moves through the sample area, and the detector continuously accumulates time-gated photons, maximizing productivity while maintaining temporal resolution.
4Productivity
If multichannel SPAD arrays are used to reduce acquisition time, then productivity is improved, but measurement precision deteriorates due to low fill factor and poorer temporal resolution
Solution Approach 1:
The patent uses a single-photon detector with very high temporal precision and applies aggressive time-gating (narrow time windows of 50-200 ps) to capture only the earliest Raman photons. This partial action (detecting only a fraction of total Raman photons within the narrow gate) compensates for the lower collection efficiency by ensuring that detected photons are overwhelmingly Raman signal with minimal fluorescence contamination, maintaining high signal-to-noise ratio while achieving reasonable acquisition times.
Data Source
AI summary
Apparatus and methods for acquiring a Raman spectral map of a sample including a material species. The apparatus includes: a pulsed illumination source providing pulsed illumination radiation for exciting the sample and producing scattered radiation; a microscope objective focusing the pulsed illumination radiation onto a region of the sample corresponding to a data point of the map, and collecting emitted radiation from the region; a translation stage translating the sample relative to the microscope objective in at least two directions; a spectral filter spectrally filtering the emitted radiation collected by the objective to obtain a filtered portion of radiation corresponding to a characteristic Raman spectral feature of the material species; a detector receiving the filtered portion and providing output electrical pulses indicative thereof; and readout electronics applying a time gate to the output electrical pulses to distinguish detection events corresponding to the Raman scattered radiation from events associated with photoluminescence.