Welche Laser gibt es im mittleren Infrarot?
Whether in environmental monitoring, medicine, industry, or research and development, mid-infrared (MIR; 2.5–25 µm = 4,000 to 400 cm⁻¹) lasers enable highly sensitive measurements. In this MIR range, molecules possess their characteristic “molecular fingerprint” and can thus be uniquely identified.
Mid-infrared lasers can include, for example, quantum cascade lasers (QCLs), which were first developed in 1994 at Bell Laboratories by Jérôme Faist, Federico Capasso, et al. Like any laser, the QCL consists of an active medium, a resonator, and a pump source. It is only through a process known as population inversion that light can be amplified and laser radiation generated.
In the case of QCLs, this type of laser features a cascade-like sequence of active regions and injection/relaxation regions consisting of quantum wells and barriers. An applied voltage injects electrons into the structure, and they tunnel between the individual stages. In each active region, stimulated emission occurs due to population inversion, generating photons (=laser light).
The electrons then pass through the injection region into the next active region, where they can once again contribute to light emission. As a result, a single electron can generate multiple photons.
The optical cavity in a QCL can be achieved in several ways. mirSense offers Fabry-Perot and distributed feedback (DFB) lasers with a spectral range from 10 to 19 µm (corresponding to 1,000 to 526 cm⁻¹). The Fabry-Perot laser is the simplest optical cavity to implement, featuring two mirrors at the ends of the laser chip. This typically results in multiple modes and a broader spectrum. In the case of mirSense, this cavity can generate laser powers of several watts. The more complex optical cavity is the distributed-feedback (DFB) laser, which produces only a single mode due to the Bragg grating. The laser beam is single-mode, and the laser power is lower compared to that of the Fabry-Perot laser. The individual wavelengths can be tuned slightly by varying the temperature.