研究目的
To demonstrate an alternative mechanism to modulate the emission from a quantum-cascade laser (QCL) device using optically-generated acoustic phonon pulses to perturb the QCL bandstructure, enabling fast amplitude modulation.
研究成果
The study demonstrated the modulation of a QCL using optically generated bulk acoustic-phonon pulses, achieving a modulation depth of up to 6%. The theoretical maximum modulation speed could be significantly higher, suggesting potential for applications in high-speed communications and high-resolution spectroscopy.
研究不足
The modulation rise-time was limited to ~800 ps by the parasitic device impedance, and the observable rise time of the THz modulation was limited by the Schottky-detector response.
1：Experimental Design and Method Selection:
The experiment involved generating acoustic strain pulses in a QCL device to modulate its emission. The methodology included the use of an aluminium-film acoustic transducer and an amplified Ti:Sapphire laser for optical excitation.
2：Sample Selection and Data Sources:
The QCL structure was based on a 9-well GaAs/AlGaAs active region emitting at a frequency of 2.5–2.75 THz. The device was processed into a surface-plasmon ridge-waveguide structure.
3：5–75 THz. The device was processed into a surface-plasmon ridge-waveguide structure.
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: Equipment included an amplified Ti:Sapphire laser, a Janis ST-100 liquid-helium cryostat, and a Virginia Diodes Schottky diode detector.
4：Experimental Procedures and Operational Workflow:
Acoustic pulses were generated in the transducer using ~40-fs pulses from the laser. The QCL was operated at a heat-sink temperature of 15 K and driven with 50-μs pulses synchronized to the 1-kHz repetition rate of the optical excitation pulses.
5：Data Analysis Methods:
The effect of the acoustic pulses on the QCL was analyzed using a time-dependent perturbation theory model to calculate the transition probabilities for resonant tunnelling between two periods of the QCL.
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