Microsecond MIRED Spectroscopy Using Pulsed Infrared Heating
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Solution Overview
Problem
The limitation of photothermal spectroscopy in achieving rapid spectral acquisition is due to the time required for cooling during temperature modulation, which restricts the effective detection bandwidth to hundreds of kilohertz per color, despite its high sensitivity and resolution.
Innovation Solution
Mid-infrared energy deposition (MIRED) spectroscopy employs a quantum cascade laser array to generate pulsed infrared light that selectively heats a sample, allowing it to cool, and uses time-resolved measurement of transient energy deposition to obtain an absorption spectrum from the first derivative of local temperature rise, enabling microsecond-scale temporal resolution and sub-micron spatial resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If photothermal spectroscopy is used to achieve high sensitivity and resolution, then detection sensitivity is improved, but spectral acquisition speed deteriorates due to cooling time requirements
Solution Approach 1:
The patent applies periodic pulsed excitation instead of continuous modulation, using microsecond-scale laser pulses to heat the sample followed by a cooling period. This periodic action allows the system to capture spectral information during the brief heating phase while the sample naturally cools between pulses, eliminating the need for continuous cooling and enabling faster spectral acquisition at hundreds of hertz to kilohertz rates.
Solution Approach 2:
The patent performs preliminary heating of the sample using ultrafast laser pulses before detection occurs. By pre-heating the sample with controlled microsecond-scale pulses and allowing it to cool naturally between pulses, the system prepares the sample in advance for detection, capturing the spectral signal during the transient heating phase without requiring continuous cooling cycles.
2Loss of information
If continuous temperature modulation is used to obtain absorption spectra, then spectral information is improved, but detection bandwidth deteriorates to hundreds of kilohertz per color
Solution Approach 1:
The patent replaces the mechanical/thermal continuous modulation system with an ultrafast optical pulse system. Instead of using continuous temperature modulation that requires slow thermal diffusion and cooling, the system uses microsecond-scale laser pulses to create transient heating, with spectra obtained from the time derivative of temperature rise. This substitution enables detection bandwidths in the hundreds of hertz to kilohertz range while preserving complete spectral information.
Solution Approach 2:
The patent changes the temporal parameters of excitation from continuous modulation to microsecond-scale pulsed action. By using ultrafast laser pulses with durations in the microsecond range and analyzing the time derivative of temperature rise, the system transforms the detection process to operate at much higher bandwidths while capturing the same spectral information that would otherwise require slow continuous scanning.
3Measurement precision
If thermal diffusion process is allowed to complete for accurate measurement, then measurement accuracy is improved, but acquisition time deteriorates to microseconds or longer
Solution Approach 1:
The patent skips waiting for complete thermal diffusion and cooling by using ultrafast microsecond-scale laser pulses to create transient heating that is measured before significant thermal diffusion occurs. The spectral information is extracted from the initial transient temperature rise phase, rushing through the measurement process in nanoseconds to microseconds rather than waiting for thermal equilibrium, thereby achieving both accuracy and speed.
Solution Approach 2:
The patent performs preliminary heating with ultrafast pulses and captures the spectral signal during the transient phase before thermal diffusion completes. By measuring the time derivative of temperature rise during the initial heating phase, the system obtains accurate spectral information without waiting for the full thermal diffusion and cooling cycle to complete.
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
MIRED spectroscopy significantly enhances detection bandwidth while preserving sensitivity and resolution, allowing for single-shot spectral acquisition and imaging with sub-micron spatial resolution, suitable for chemical analysis in dynamic environments and complex systems.
Implementation Method 1
selectively heats the sample by absorption of the pulsed infrared light
Implementation Method 2
selectively heats the sample by absorption of the pulsed infrared light
Implementation Method 3
despite the extremely high sensitivity and resolution offered by photothermal detection
Implementation Method 4
computes a time rate of local temperature rise in the sample to obtain instantaneous absorption in the sample
Data Source
AI summary
A spectroscopy and microscopy system and method include a source of pulsed infrared light generating pulsed infrared excitation light for exciting a sample, such that the pulsed infrared light selectively heats the sample by absorption of the pulsed infrared light and allows the sample to cool. A source of probe light generates probe light for illuminating the sample. A detection element detects a signal indicative of selective heating of the sample by the excitation light. A processor receives the signal indicative of the selective heating of the sample, computes a time rate of local temperature rise in the sample to obtain instantaneous absorption in the sample, and, using the instantaneous absorption, generates a spectrum related to the sample.