High performance quantum cascade lasers in the 3-5 um spectral range
Electrical and Computer Engineering
Digital Signal Processing
Friday, January 20, 2012
11:00 AM to 12:00 PM
202 Space Science Building
Rice University
6100 Main St
Houston,Texas,USA
Recently, the need for compact sensors, capable of real-time concentration monitoring, has become crucial. For this reason nowadays a strong interest is shown in the optimization of low-consumption quantum cascade lasers (QCLs) and in particular on the improvement of their power efficiency. QCL performance is strongly dependent on the careful optimization of the active region design. Therefore a reliable simulation model is important to predict laser behaviour. In our group a new transport model has been developed[1] that can not only model intraperiod electron dynamics, e.g. scattering times, but it is also able to estimate actual laser performance, i.e. the output power and the voltage-current characteristic. This method enormously eases the route to an efficient and fast optimization of the laser design. One of the key elements to be addressed in designing a QCL structure is the optimization of the injector efficiency in to the upper lasing state. This is particularly crucial for lasers in the short wavelength range (3-5 µm). In this case the high electric field needed to align the injector ground state with the upper lasing transition, leads to relevant parasitic currents flowing in the structure already before the levels align. To reduce these leakage currents, while maintaining an efficient coupling of the injector state with the upper lasing state, new designs based on composite injector barriers (Step Well designs) will be introduced. This design show a relevant improvement of the laser efficiency.
Among the first atmospheric window, the 3-4 µm spectral region is particularly interesting for industrial applications since the fundamental C-H, N-H and O-H stretching modes have strong resonances in this region(e.g. Methane, Formaldehyde). Unfortunately for wavelengths smaller than 4 µm, the realization of QCLs is challenging using the standard material systems due to the large conduction band discontinuity needed.
The development of Sb-free QCL designs based on the InGaAs/AlInAs-AlAs on InP material system emitting in the 3-4 µm range will be presented. Maximum operation temperature above 350K will be presented at 3.3 µm with watt-level performance[2]. Previously, no QCL with emission wavelength smaller than 3.6 µm was demonstrated in this material system in a temperature accessible by thermoelectric cooling[3]. Moreover, using an external cavity configuration, spectral tuning over more than 275 cm-1 has been observed in pulsed operation.
The use of this material system(InGaAs/AlInAs-AlAs) is particularly appealing since it is the only one Sb-free in this spectral range and it is fully compatible with the high-performance QCL fabrication processes for continuous wave emission, i.e. buried heterostructure process(BH). Preliminary results on the distributed feedback BH lasers will also be presented. Single mode emission at room temperature will be presented.
[1] R. Terazzi, and J. Faist, New Journal of Physics 12, 033045 (2010).
[2] A.Bismuto,M.Beck,J.Faist Appl.Phys.Lett.98,191104(2011).
[3] J.Faist,F.Capasso,D.Sivco,A.Hutchinson,S.Chu, A.Cho Appl.Phys.Lett.72,680(1998).
Host: Frank K. Tittel (AL A237 x4833)