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Semiconductor Physics Group


Mode locking

Indirect evidence of active and passive mode-locking has been reported by research at Bell Laboratories using mid-IR QCLs [1,2]. Time resolved measurement of the optical pulse is still a challenge to verify the mode locking conditions. Photoconductive optical gating technique is typically used for coherent detection of broadband THz pulse waveforms. A photoconductive antenna, a micro-gap gold electrodes deposited on a LT-GaAs, is irradiated by femtosecond laser pulses generating photocarriers. The photocarriers are accelerate by THz pulses from QCLs resulting in photocurrent. By changing the delay time between the THz pulse and the optical pulse, the temporal THz pulse shape can be reproduce from the detected current signal. We apply this technique to systematically study the properties of mode-locked QCLs. Our target is to realise mode-locked QCLs for the generation of high power THz pulses with ultrashort pulse widths.

A picture of our set-upFigure 1: A picture of our set-up.

References: [1] R. Paiella et al., Science 290 (2000) 1739. [2] R. Paiella et al., Appl. Phys. Lett. 77 (2000)169.