Interferometric Optical Path Scanning With Rotating Mirror Feedback
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Solution Overview
Problem
Conventional terahertz wave analysis techniques require long integration times due to the use of lock-in amplifiers and thermal detectors with slow responses, leading to prolonged measurement durations.
Innovation Solution
An interferometric measurement apparatus that uses a rotating mirror to quickly change the optical path length difference by monitoring the beam position on a third mirror, employing reference light for beam position monitoring to prevent interference reduction and ensure stability, and utilizing pulsed light generation for efficient measurement light production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a lock-in amplifier is used to measure the temporal waveform of terahertz waves, then measurement accuracy is improved, but measurement time is prolonged due to long integration time requirements
Solution Approach 1:
The patent replaces the conventional lock-in amplifier detection method with an interferometric measurement system using a beam splitter, mirrors, and a fast detector. This substitution eliminates the need for long integration times by using optical interference patterns to encode measurement information, enabling rapid acquisition of temporal waveform data while maintaining measurement accuracy.
Solution Approach 2:
The patent employs periodic modulation of the optical path length using a rotating mirror or moving mirror mechanism in the interferometer. By scanning the optical path difference periodically and detecting the interference pattern at different path lengths, the system rapidly captures temporal waveform information without requiring long integration times, thus resolving the contradiction between measurement accuracy and measurement speed.
2Reliability
If thermal detectors are used to detect terahertz waves, then detection capability is improved, but response speed deteriorates leading to prolonged measurement duration
Solution Approach 1:
The patent substitutes thermal detectors with fast photodetectors or bolometers that have significantly shorter response times. The interferometric measurement system uses these fast detectors to capture the temporal waveform of terahertz waves by measuring the intensity of interference patterns at different optical path lengths, thereby achieving both reliable detection and rapid response.
Solution Approach 2:
The patent introduces dynamic scanning of the optical path length using a moving mirror or rotating polygonal mirror. This dynamic approach allows the system to rapidly sample the temporal waveform by varying the optical path difference over time, enabling fast response detection without sacrificing detection capability.
3Measurement precision
If the second mirror is moved parallel to the mirror surface to change optical path length, then optical path length control is improved, but measurement speed deteriorates
Solution Approach 1:
The patent employs a rotating polygonal mirror or rotating single mirror instead of translating the mirror parallel to its surface. By rotating the mirror, the optical path length is changed more rapidly through angular displacement, which converts linear motion into rotational motion. This dynamic approach maintains precise optical path length control while significantly increasing the speed at which different path lengths can be scanned, thus resolving the contradiction between control precision and measurement speed.
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
Enables rapid and accurate interferometric measurement in the mid-infrared and terahertz regions by indirectly measuring the optical path length difference through beam position monitoring, improving measurement speed and accuracy.
Implementation Method 1
a beam splitter that splits the measurement light output from the light source into a first split light and a second split light
Implementation Method 2
an interferometric optical system that combines the first split light and the second split light re-entered into the beam splitter; a first detector sensitive to the wavelength of the measurement light and configured to detect interference light of the measurement light generated by the combination
Implementation Method 3
the second mirror is configured to be rotationally driven to change an optical path length of the second optical path; the analysis unit is configured to monitor a beam position corresponding to a light incident position on the third mirror displaced according to rotation of the second mirror
Implementation Method 4
the optical component is configured to condense or collimate the second split light from the second mirror
Data Source
AI summary
An interferometric measurement device includes an interferometric optical system that includes a beam splitter that splits the measurement light into a first and second split lights, a first optical path that reflects the first split light and re-enters it into the beam splitter, and a second optical path in which the second split light is folded back by a mirror member via a rotating mirror, wherein the interferometric optical system combines the first and second split lights re-entered into the beam splitter, a photomultiplier tube that detects the interference light of the first and second split lights, and an analysis unit that acquires a signal waveform that associates a measurement value of the detected interference light with an optical path length difference. The analysis unit monitors the beam position displaced according to the rotation of the rotating mirror and acquires the signal waveform based on the beam position.