Anhui University used QCL to achieve precise NO2 measurement

Abstract

Prof. Sheng Zhou from Anhui University published a paper called  "Measurement of Line Intensities of NO₂ Near 6.2μm by Quantum Cascade Laser Spectrometer" in the Journal of Quantitative Spectroscopy & Radiative Transfer. HealthyPhoton participated in the experiment and provided the quantum cascade laser (QCL) and drive control products for the experiment.

Figure 1. Screenshot of the first page of the paper

Application

Nitrogen dioxide (NO₂) is a common pollutant that mainly comes from fossil-burning fuels, lightning, and microbial life activity in the soil. NO₂ can cause photochemical smog, which leads to an increase in rain acidity. Exposure to high concentrations of NO₂ continuously may cause a variety of short - and long-term adverse effects on the respiratory system of humans and animals. Therefore, the development of a cost-effective, stable, and sensitive system for NO₂  monitoring is extremely important.

Chemiluminescence and wet chemical analysis are the most common detection methods o for NO2 detection. However, these methods have a slow response time and are unable to accurately distinguish NO and NO₂, thus their applications are very limited. The optical method based on absorption spectrum provides a powerful analytical method for trace gas analysis which ensures extremely high sensitivity, high selectivity, and rapid response. 

NO₂ has a distinct absorption spectrum in both UV-Vis and IR regions. It is more suitable for the detection of NO₂ using the IR band since its vibrational rotation spectrum in the IR band is simple and has no overlap with other molecules. Due to the fundamental frequency absorption of most atmospheric molecules is located in the mid-IR band, the laser absorption spectroscopy based on the mid-IR band is an ideal choice for analyzing trace gases. Commercial  continuous wave(CW)  QCLs have been widely used in the quantitative spectral analysis of NO₂. These lasers have the advantages of high output power, room temperature (RT) operation, extremely narrow line-widths, and wide spectrum tun-ability.

Figure 2. Experimental setup based on CW-QCL laser spectrometer:

HealthyPhoton’s products are highlighted in the green boxes

Figure 3. HealthyPhoton’s product applied to this project

- All-in-one module includes both current driver and temperature controller

- Linear output to TEC greatly extends the Peltier device lifetime

- Output protection mechanisms ensure the safety of QCL chip: adjustable current clamp, output ramp start, over-voltage and under-voltage protection, over temperature protection and short-circuit output protection

- Touchscreen UI is convenient for user operation and status monitoring

- It is easy to set up and fully compatible with HealthyPhoton’s QCL emitter module (HPQCL-Q)

- Compact package specially designed for Quantum Cascade Lasers

- Output beam collimated and extremely low optical interference fringes

- Integrated semiconductor TEC temperature control and low-noise air fan with 20W heat dissipation capability, ensuring constant chip temperature

- Output optical power can reach up to 100 mW

- Compatible with QC750-Touch^TM QCL driver

- Cables and connectors included

- Sensitive to mid-IR light from 2 ~ 12 µm

- Signal bandwidth: DC/AC ~ 20 MHz

- TEC to hold the temperature at ~190K that greatly reduces thermal noise

- Low-noise, wide-bandwidth pre-amplifier to convert photocurrent into a voltage signal

- Cost-effective

Reference