Wavelength Modulation Technology Research Articles

Application of calibration-free wavelength modulated spectral absorption technique in temperature measurement under ultra-short optical path

The measurement of gas temperature parameters is of great significance in scientific research and industrial production. Wavelength modulation technology, as a non-contact optical detection means, has the characteristics of strong anti-interference ability and is widely used in various complex and harsh environments. The accuracy of temperature measurement is affected by short optical paths and weak absorption. In this paper, a calibration-free wavelength modulated ultra-short optical path measurement system is established, and the selection rules of spectral lines under the ultra-short optical path and weak absorption are proposed. The measurement results of wavelength modulation without calibration are in good agreement with those of thermocouple temperature measurement, and the relative error is less than 10%.

Research on Multi-point Measurement System of Mine Gas Based on TDLA

Tunable Diode Laser Absorption Spectroscopy (TDLAS) technology combines the advantages of wavelength modulation technology and direct absorption spectroscopy technology, and the system achieves highly sensitive and full-range detection of methane gas concentrations. In the system, only the pure optical methane probe is positioned under the mine, which establishes connectivity with the host computer on the surface through the optical fiber. This setup enables the simultaneous detection of 16 channels of methane gas through time-sharing multiplexing technology. Experimental results demonstrate a measurement error of less than ±6.0×10−4 at low concentrations (0∼1%) and within ±6% of the true value at high concentrations under normal temperature and pressure conditions. The full-range linear fit attains 0.9998. According to the one-fold standard deviation, the minimum detection lower limit of the system stands at 68.36 ppm and the measured gas concentrations across different channels of the methane probes remain consistent inhe same environment. This technology provides a new solution for continuous, accurate, and multi-point monitoring of mine gas.

Active noise reduction for a differential Helmholtz photoacoustic sensor excited by an intensity-modulated light source.

A highly sensitive differential Helmholtz photoacoustic sensor with active noise reduction was reported. Coupled to one cavity of the photoacoustic cell, an intensity-modulated excitation light would reflect multiple times to produce photoacoustic signal, and meanwhile cause the solid-state photoacoustic effect forming differential mode noise with the frequency same as the photoacoustic signal, which could not be suppressed by conventional differential technology. Wavelength modulation technology is a splendid method to restrain this effect, which is not suitable for light sources with not adjustable wavelength. To suppress this kind of noise, an intensity-modulated compensation light was coupled to another cavity, whose central wavelength was at the non-absorption line of the measured gas. The compensation light was of the same frequency, phase, and power as the excitation light, by which the solid-state photoacoustic effects were produced to form destructive interference called active noise reduction. The experiment results showed that the active noise reduction significantly improved the signal-to-noise ratio and signal-to-background ratio. Compared with the differential, the differential with active noise reduction improved signal-to- noise ratio by about 1.2 times and signal-to-background ratio by about 9.4 times. When low-power near-infrared lasers were employed as the two light sources, the minimum detection limits for acetylene and methane reached 21 and 200 ppb, respectively.

Design of a high-sensitivity differential Helmholtz photoacoustic cell and its application in methane detection.

A high-sensitivity differential Helmholtz photoacoustic cell based on multiple reflection was reported, and its performance parameters and gas replacement time were optimized by finite element simulation. To realize the long absorption path of the measured gas, the collimated excitation light was reflected multiple times on the gold-plated wall of the absorption cavity, and the wavelength modulation technology was used to reduce the multiple reflection noise. Additionally, the differential could suppress external co-phase noise and double the photoacoustic signal. When a laser with a central wavelength of 1653 nm was employed as the excitation light source, the minimum detection limit of 177 ppb (signal-to-noise ratio, SNR = 1) for methane was achieved within a detection time of 1 s, and the corresponding normalized noise equivalent absorption coefficient was 4.1×10-10 cm-1WHZ-1/2.

A methane telemetry sensor based on near-infrared laser absorption spectroscopy

In order to detect methane leakage accurately and prompt, a methane telemetry sensor is demonstrated based on near infrared absorption spectroscopy and optimized wavelength modulation technology. The distributed feedback diode laser is applied as the light source to cover the selected absorption line of 6046 cm−1 to reduce the interference of CO2 and H2O. The waveform generator and the digital quadrature lock-in amplifier are constructed by the FPGA to produce driving signals and extract WMS-1f and 2f signals. And the “2f/1f” method is adopted to eliminate the environment influence such as light intensity fluctuations and improve the signal-to-noise ratio. This methane sensor has the characteristics of fast response and strong resistance to environmental interference and has great application prospect.

基于免标定波长调制技术的高温谱线参数测量方法

基于免标定波长调制技术的高温谱线参数测量方法

Photoacoustic Compound Fire Alarm System for Detecting Particles and Carbon Monoxide in Smoke

In view of the high sensitivity and high selectivity of photoacoustic technology, a compound fire alarm system used for detecting smoke particles and carbon monoxide was designed on the basis of the photoacoustic spectrometry principle. The system uses an infrared laser with a central wavelength of 1579 nm as the light source, adopts wavelength modulation technology to modulate the continuous light source, and moves the inspection frequency to high frequency with lower noise by integrating harmonic detection technology, thus realizing a measurement of the photoacoustic signal. Concurrently, the system obtains the CO concentration and extinction coefficient of smoke particles via inversion by using the measured scattered light intensity data combined with a certain algorithm. A test was carried out on the system by using three small-scale experiments, namely, cotton rope smoldering fire, polyurethane foam fire and sandalwood smoldering fire. The results show that the CO gas concentrations and extinction coefficient of smoke particles produced by these three experiments are well detected. The CO detection limit of the system was 2.98 ppm. The test results also show that pure powder (used for simulating particles) or pure CO gas will not trigger the system alarm, so unnecessary alarms caused by traditional fire detectors can be avoided and the reliability of the fire alarm can be improved.

基于二次谐波调制技术提高HONO测灵敏度的方法研究

基于二次谐波调制技术提高HONO测灵敏度的方法研究

波长调制技术中光强调制对二次谐波线型的影响研究

波长调制技术中光强调制对二次谐波线型的影响研究

Kinetic Analysis of the Interaction between Nonsteroidal Anti‐inflammatory Drugs and Cyclooxygenase‐2 Using Wavelength Modulation Surface Plasmon Resonance

AbstractA surface plasmon resonance (SPR) biosensor based on wavelength modulation technology was developed and validated for the kinetic analysis of the interactions between two nonsteroidal anti‐inflammatory drugs (NSAIDs) and cyclooxygenase‐2 (COX‐2). After the effect of different concentration COX‐2 on the binding capacity of the SPR biosensor surface was studied, the COX‐2 was immobilized covalently onto the biosensor surface using a standard amine coupling method. The affinity constants for indomethacin, ketoprofen binding to COX‐2 are 7.5×103 L/mol and 9.25×103 L/mol, respectively. The biosensor surface can be regenerated after being rinsed with 0.01 mol/L NaOH, and the biosensor can be used repeatedly. These indicated that the wavelength modulation SPR biosensor has the potential application in the fields of pharmacokinetics, pharmacodynamics and drug discovery.

Tunable and frequency-stabilized diode laser using temperature-dependent energy pooling fluorescence

We have demonstrated a robust method of tuning and stabilizing a diode laser frequency to the fluorescence peaks of the energy pooling occurred at thermal cesium vapor-glass interface. This technique is based on temperature-dependent shift of the two off-core fluorescence peaks caused by 6P3∕2+6P3∕2→7P(3∕2,1∕2)∕8S1∕2+6S1∕2 energy pooling collisions. We achieved laser linewidth of 1.1MHz and continuous tunability over ±200–600MHz within a temperature range of 360–420K by applying the wavelength modulation technology. Tunable frequency locking in such a wide range was constructed inexpensively with low laser power. It can also be extended to other wavelengths by using different atomic species.

Experimental investigation of the sub-Doppler transmission spectroscopy in a thin vapour layer at room temperature

The sub-Doppler transmission spectrum in a thin vapour layer (about 150 μm) was observed at room temperature using the wavelength modulation technology. The absorption signal and its second-order harmonic were detected with an external-cavity diode laser. A sub-Doppler spectrum corresponding to resonant transitions of the caesium D2 line (6S1/2→6P3/2) was demonstrated. The dependence of the transmission signal on the intensity of the laser was also investigated.