Spectral gain profile of a multi-stack terahertz quantum cascade laser

Abstract

The spectral gain of a multi-stack terahertz quantum cascade laser, composed of three active regions with emission frequencies centered at 2.3, 2.7, and 3.0 THz, is studied as a function of driving current and temperature using terahertz time-domain spectroscopy. The optical gain associated with the particular quantum cascade stacks clamps at different driving currents and saturates to different values. We attribute these observations to varying pumping efficiencies of the respective upper laser states and to frequency dependent optical losses. The multi-stack active region exhibits a spectral gain full width at half-maximum of 1.1 THz. Bandwidth and spectral position of the measured gain match with the broadband laser emission. As the laser action ceases with increasing operating temperature, the gain at the dominant lasing frequency of 2.65 THz degrades sharply.

Dynamics of a broad-band quantum cascade laser: from chaos to coherent dynamics and mode-locking

“…In this way we recover the two-level description by setting α = 0. The real constants f 0 , α, Γ can be obtained by fitting the experimentally measured gain spectra reported for example in [8,36] around their maxima [24]. By using relations (8) and (11) in Eqs.…”

Influence of dimensional static and dynamic charges on conduction in the active zone of a quantum cascade laser

“…Nowadays, development of semiconductor technology and physics is closely related with researches in quantum cascade lasers (QCL) and detectors [1][2][3][4][5][6][7][8] as well as physical processes in them.…”

Dispersion in a broadband terahertz quantum cascade laser

“…The experimental method is based on a TDS system in combination with a coupled cavity sample geometry. [26][27][28] Using this approach, we are able to monitor changes of the total GVD as a function of the intersubband gain in the QC structure. The gain induced GVD appears to be the dominant contribution to the total GVD with respect to the ones of the material and the The studied device employs the heterogeneous active region presented in Refs.…”

“…The GVD oscillation with peaks at 2.64 and 2.86 THz is most likely caused by the alignment of the active region stack with the highest emission frequency, as reported previously. 5,17,27 The steep slopes in the GVD curves below 2.0 THz and above 3.0 THz mark the limits of the experimental bandwidth. The shaded areas bound between 62.5 Â 10 4 fs 2 /mm act as guides for the eye.…”

“…A hyperhemispherical silicon lens was attached to the output facet in order to improve the beam quality and the intensity, both necessary to boost the signal-to-noise ratio (SNR) of the TDS measurements. 26,27,29 To suppress the higher order lateral modes in the laser, lossy side-absorbers were implemented to the edges of the metal-metal waveguide. 18 The used TDS setup, as shown in Fig.…”