TDLAS optical solution
Publish:Box Optronics  Time:2023-05-11  Views:692

Technical Principles

The spectrum of the semiconductor laser light source used in TDLAS technology is much wider than the broadening of the gas absorption spectral line, resulting in a single line absorption spectrum. Therefore, TDLAS technology is a high-resolution absorption spectroscopy technology.

When selecting the absorption spectral line, it should be ensured that there are no absorption spectral lines of background gas components in the measurement environment within a range of approximately 10 times the spectral line width near the selected absorption spectral line frequency, in order to avoid cross absorption interference of these background gas components on the measured gas and ensure measurement accuracy. For example, in Figure 1, there is no H2O absorption line near the CO absorption line located at the frequency of 6408cm-1, so the measurement of moisture in the environment will not interfere with the measurement of CO.

The principle of "single line spectrum" measurement technology

The laser beam passes through a gas medium with a length of L, a pressure of P, a temperature of T, and a concentration of X. The absorption of the laser by the gas medium meets the Beer Lambert law, which means that the measured component has absorption of light at a specific wavelength, and the absorption intensity is proportional to the component concentration.

TDLAS is combined with phase-sensitive detection technology to quickly modulate the laser frequency to sweep over a certain frequency range of the gas absorption spectral line being measured. Then, phase-sensitive detection technology is used to measure the harmonic components in the transmitted laser intensity absorbed by the gas absorption spectral line to analyze the gas absorption. Modulation spectroscopy technology can achieve good detection sensitivity by effectively compressing the noise bandwidth.

Principle of in-situ measurement

The laser gas analysis system can be directly installed on pipelines, achieving true non-contact in-situ measurement.

During installation, only the transmitting and receiving units need to be aligned and fixed on both sides of the tested flue gas pipeline through standard flanges to achieve online real-time flue gas analysis. The laser beam emitted by the emission unit passes through the measured gas and is received by the photoelectric detection sensor installed in the receiving unit in the opposite direction of the pipeline. The obtained measurement signal is processed to obtain concentration information. The analysis system is equipped with auxiliary equipment such as a blowing system and explosion-proof system. The purging system controls industrial nitrogen gas to purge the optical window of the emission and reception units, avoiding long-term pollution of the optical window by dust in the gas, resulting in a significant decrease in laser transmission light intensity. The explosion-proof system enables the instrument to meet explosion-proof requirements and can be installed in explosive industrial environments. During maintenance, only dust and stains on the glass slides at both ends of the transmitter and receiver need to be wiped clean. The maintenance amount is very small and the cycle can reach more than three months.


TDLAS abstimmbare Halbleiter-Laser-Absorptionsspektroskopie-Technologie kann berührungslose Messungen erreichen und ist weit verbreitet für Gaskonzentrationsmessung und -steuerung in rauen Industrieumgebungen verwendet. Je nach Kundenwunsch können auch verschiedene industrielle Parameter wie Temperatur, Druck, Durchfluss usw. gemessen werden.

Bokos Optoelektronics konzentriert sich seit langem auf die Anwendung der Laserspektroskopie auf dem chinesischen Markt. Speziell in Laserabsorptionsanwendungen wie Gasmolekularspektroskopie und Kaltatomspektroskopie können wir Kunden nach mehr als zehn Jahren Anstrengung nun eine Produktlösung aus einer Hand anbieten, einschließlich Laserlichtquellen (Eagleyard), Detektoren, Laserdiodentreiber und Temperaturregler (Wellenlängenelektronik).