Interferometric Device Phase Control Infrared Spectroscopy
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Solution Overview
Problem
Current spectroscopic methods in the infrared spectral range face low sensitivity, especially for small analyte concentrations, and require multiple measurements for each wavelength, leading to instability and inability to record spectra due to optical path length fluctuations and high water absorption.
Innovation Solution
An interferometric device with a tunable laser, beam splitting and combining elements, and phase control, generating differential signals with 180° phase shift to regulate and compensate for intensity fluctuations, allowing for precise refractive index determination and spectrum recording.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a difference signal is detected from destructive interference of measuring and reference beams, then laser intensity verification is achieved, but sensitivity approaches zero for small analyte concentrations
Solution Approach 1:
Instead of using destructive interference to generate a difference signal (which gives zero sensitivity for small analyte concentrations), the patent inverts the approach by using constructive interference to generate a sum signal. This inversion allows the measurement to detect small changes in optical path length with high sensitivity, as the sum signal maintains a strong baseline that small perturbations can effectively modulate.
Solution Approach 2:
The patent changes the measurement parameter from difference signal (destructive interference) to sum signal (constructive interference). This parameter change transforms the measurement regime from one with zero sensitivity for small analytes to one with high sensitivity, while still maintaining laser intensity verification through the ratio of sum to difference signals.
2Measurement precision
If two measurements are performed for each wavelength (with and without sample), then optical path length matching is achieved, but measurement time increases and stability decreases due to optical path length fluctuations
Solution Approach 1:
The patent implements continuous wavelength scanning with simultaneous measurement in both interferometer arms, eliminating the need to switch between sample and reference measurements. The tunable laser continuously sweeps through the wavelength range, and the interferometer continuously records interference patterns, maintaining uninterrupted measurement flow and eliminating time losses from repeated optical path length adjustments.
Solution Approach 2:
The patent performs preliminary calibration by establishing the relationship between phase actuator position and wavelength at the beginning of the measurement sequence. This preliminary action creates a lookup table or calibration curve that allows direct conversion of phase actuator readings to wavelength values throughout the measurement, eliminating the need for repeated wavelength verification during the measurement process.
3Reliability
If optical path length is set to the same value for both paths, then interferometric superposition is achieved, but fluctuations in optical path length impair measurement results
Solution Approach 1:
The patent implements feedback control by continuously monitoring the interference signal and adjusting the phase actuator position to maintain optimal superposition conditions. The system detects deviations from the expected interference pattern caused by optical path length fluctuations and actively compensates by adjusting the phase actuator, thereby maintaining stable measurement conditions despite environmental perturbations.
Solution Approach 2:
The patent introduces a phase actuator as an intermediary element that mediates between the optical paths and the detection system. This phase actuator serves as a controllable variable that can compensate for optical path length differences, acting as a buffer that isolates the measurement from fluctuations in the optical paths while maintaining the ability to achieve precise interferometric superposition.
4Adaptability or versatility
If a tunable laser is used for wavelength adjustment, then spectrum recording is enabled, but the system requires two paths of different lengths which conflicts with equal path length requirement
Solution Approach 1:
The patent employs dynamic path length adjustment using a phase actuator that can change the optical path length in real-time during wavelength scanning. This dynamic adjustment allows the system to maintain equal physical path lengths while compensating for the effective path length differences that would otherwise be required for wavelength-tuned interferometry, thereby simplifying the optical configuration while preserving spectral measurement capability.
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
Enhances sensitivity and stability for qualitative and quantitative analysis of liquid samples by controlling the phase difference between measuring and reference beams, enabling accurate refractive index spectrum detection and compensation for laser intensity fluctuations.
Implementation Method 1
a beam splitting element for splitting the laser beam into a measuring beam and a reference beam
Implementation Method 2
a beam merging element with a first output for interferometric superposition of the measuring beam and the reference beam as the first output beam and with a second output for interferometric superposition of the measuring beam and the reference beam as the second output beam, wherein the first output beam and the second output beam differ from each other by 180° in phase
Implementation Method 3
A phase adjuster for setting the phase between the measuring beam and the reference beam
Implementation Method 4
a first detector for detecting the first output beam; a second detector for detecting the second output beam
Data Source
Figure 1~2
Figure 3~5
AI summary
The invention relates to a method and an interferometric device (1) for spectroscopically or spectrometrically examining a sample, preferably in the infrared spectral range, comprising the steps: a) generating a laser beam (3) having a wavelength preferably in the infrared spectral range, b) splitting the laser beam (3) into a measurement beam (6) and a reference beam (7), c) interacting the sample with the measurement beam (6), d) interacting a reference with the reference beam (7), e) overlaying the measurement beam (6) and the reference beam (7) such that both a first output beam (18) and a second output beam (19) are obtained, the phases of which are displaced relative to one another about 180°, f) detecting the first output beam (18), g) detecting the second output beam (19), h) forming a differential signal (28) between the first output signal (18) and the second output signal (19), i) controlling the differential signal (28) to a predefined target value (30) by adjusting a phase difference between the measurement beam (6) and the reference beam (7), j) determining a refractive index (n) of the sample from the adjustment of the phase difference between the measurement beam (6) and the reference beam (7), k) repeating steps a) to j) for additional wavelengths of the laser beam (3) preferably in the infrared spectral range in order to detect a spectrum of the refractive index (n) of the sample.