Terahertz quantum cascade lasers (QCLs) have narrow linewidths
(< 1 MHz) and electrical/thermal tuning ranges of several GHz. This combination allows high resolution laser absorption spectroscopy at frequencies between 1.9 and 5 THz.
At frequencies above 3 THz, the terahertz QCL is the only source capable of these measurements. For additional, broader tuning, additional devices can be integrated in a simple, electronically controlled package.In a tunable diode laser spectroscopy configuration, a single-modeQCL is operated in continuous-wave mode and electronically/thermally tuned across the absorption lines of low pressure gasses in a gas cell.
A small AC signal is added to the QCL bias causing small frequency oscillations. As the laser is tuned across the absorption line, this oscillation is detected by a lock-in amplifier referenced to the frequency of the AC signal. This results in a measurement of the first derivative of the absorption line. Alternatively the lock-in amplifier can be referenced to the first harmonic of the AC signal, resulting in a measurement of the second derivative of the absorption line (2f spectroscopy), as shown here with a methanol (CH3OH) gas cell.
Real-Time THz Imaging
Due to high average power (>1mW-10mW) provided by LongWave Photonics EasyQCL System, real-time terahertz imaging through dielectric and bio-materials is now possible with THz focal array imager and proper imaging system setup.
At certain frequencies where air absorption of terahertz wave is low, stand-off distance (>25m) imaging is also achievable.
Please contact us to discuss any special needs in your project.
Through the help of external PID control loop, the linewidth of Terahertz quantum cascade lasers can be further reduced within sub-kHz range. Combing with high optical beam quality and above mW level CW power, LongWave Photonics THz DFB QCL source is suitable as the local oscillator to pump various types of mixers used in THz heterodyne detection system.
Please contact us for more information about how to intergrate EasyQCL system into your heterodyne setup.
Herschel Space Observatory is using heterodyne detection at Terahertz freqeuncies to study the formation and evolution of galaxies.