Introduction to TDLAS and QCL


Tunable Diode Laser Absorption Spectroscopy (TDLAS)

    Mid/far-infrared (Mid/Far-IR) laser spectroscopy is based on a principle called Tunable Diode Laser Absorption Spectroscopy (TDLAS). It uses the "frequency-selective" absorption of different gas molecules to form an absorption spectrum. All gas molecules have their unique absorption spectra, which can be regarded as their fingerprints. Therefore, TDLAS technology can achieve a high-resolution and anti-interference quantitative analysis of molecular concentration. 
    The basic method of Mid/Far-IR laser spectroscopy is to tune the wavelength of a specific semiconductor laser source, typically Quantum Cascade Laser (QCL) or Interband Cascade Laser (ICL), to scan the specific absorption spectrum line of the gas molecule to be measured. The transmitted light absorbed by the gas is received by the photodetector. Sometimes, small modulation to the laser scanning current is added and a phase-locked amplifier module extracts the harmonic component of the signal received by the photodetector. Finally, the gas concentration is retrieved based on calibration coefficients from a signal processing module.

Quantum Cascade Laser (QCL)

    Born in the famous Bell Labs in 1994, QCL is a new type of unipolar semiconductor laser based on the principle of electron transition between conduction band and subband in semiconductor quantum well and phonon-assisted resonance tunneling. The working principle of QCL is fundamentally different from the traditional near-infrared diode laser. Its wavelength can cover most of the mid-to-far infrared spectral region. 
HealthyPhoton uses the world's leading semiconductor QCLs as infrared laser sources. Combined with our proprietary signal processing technology, the fundamental transitions of molecules with wavelengths in the mid/far-infrared region are efficiently detected, which enables unprecedented precision and stability. This technology is used in a wide range of applications, including industrial process control, atmospheric environmental monitoring, medical diagnosis,  and ecological research.

    Many gas species have stronger absorption peaks in the Mid-IR region. Hence, the use of QCLs leads to higher accuracy of laser-based gas analysis technology.

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