Achieving light output in the MIR wavelength region (3-10 microns) is no easy task. Typical laser diode materials are physically incapable of providing such wavelengths, so many people end up choosing thermal sources for IR radiation. However, when it comes down to it, only so much radiant power comes from thermal emission, and that’s where QCLs come in. Utilizing precise design of “quantum wells” that can be angstroms wide, a QCL’s active regions containing these wells provide the conditions for “tunneling.” Voltage drives electrons across these active regions, and due to this quantum phenomenon, IR photons are emitted when electrons reach lower energy states (Fig. 1). QCLs provide far more output power than thermal sources, which really comes in handy in highly analytical applications.
Figure 1. Quantum wells in a quantum cascade laser (QCL)
As one could imagine, quantum wells are not so easy to produce in QCLs. Chip design and growth are largely a batch process, and unfortunately, yields can be quite low. The process from growth to testing can be quite labor intensive as well. Hamamatsu acknowledges that cost is barring QCLs from new markets, so we developed a low-cost butterfly package (Fig. 2).
Figure 2. Low-cost QCL in a butterfly package
When it comes to optimizing performance, most of the work is actually done before the laser is delivered. No matter the vendor, a deep and thorough discussion concerning specifications needs to be had before proceeding. Aligning on specifications ensures the application needs are met while also ensuring the lowest cost.
With the laser in hand, many tend to ignore the importance of electronics. Noise from TEC controllers and laser drivers can deeply hamper measurements; using higher performing electronics usually pays dividends down the line.
There is also the issue of heat load. Dependable temperature control is crucial for a QCL, so a properly designed heatsink is critical.
Gary Spingarn is a Product Manager in the New Jersey office of Hamamatsu, where he focuses on business development for certain products and exploring new applications. Leveraging his chemistry expertise, Gary supports the mid-infrared (MIR) product lines with a particular knack for process monitoring, gas analysis, and environmental applications. In his spare time, Gary hones his chess skills as well as partakes in strength sports and world travel.
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