Measuring the sampling coherence of a terahertz quantum cascade laser

Abstract

Abstract:The emission of a quantum cascade laser can be synchronized to the repetition rate of a femtosecond laser through the use of coherent injection seeding. This synchronization defines a sampling coherence between the terahertz laser emission and the femtosecond laser which enables coherent field detection. In this letter the sampling coherence is measured in the time-domain through the use of coherent and incoherent detection. For large seed amplitudes the emission is synchronized, while for small seed amplitudes the emission is non-synchronized. For intermediate seed amplitudes the emission exhibits a partial sampling coherence that is time-dependent. 211-212 (1982). 4. A. Nahata, A. S. Weling, and T. F. Heinz, "A wideband coherent terahertz spectroscopy system using optical rectification and electro-optic sampling," Appl. Phys. Lett. 69(16), 2321-2323 (1996). 5. J. Dai, X. Xie, and X. C. Zhang, "Detection of broadband terahertz waves with a laser-induced plasma in gases," Phys. Rev. Lett. 97(10), 103903 (2006). 6. D. H. Auston and K. P. Cheung, "Coherent time-domain far-infrared spectroscopy," J. Opt. Soc. Am. B 2(4), 606-612 (1985). 7. C. A. Schmuttenmaer, "Exploring dynamics in the far-infrared with terahertz spectroscopy," Chem. Rev. 104(4), 1759-1780 (2004). ©2012 Optical Society of America 41(3),

Electric field sampling of modelocked pulses from a quantum cascade laser

“…The effect the optical seed on the laser operation is thought to be important only for the first ∼500-ps of the emission; in ref. [13] it was found that a seed pulse will decrease the build-up time of the emssion, these results we confirmed by simulations, which additionally showed that after this start-up time, the emission closely resembles the 'free-running' emission [14]. From QCL output power measurements we estimate that the gain-switching pulse provides 200mA, so the threshold for the quasi-DC when the pulse applied is 445 mA.…”

Detection of terahertz frequency radiation via the photothermoelastic response of zincblende crystals

“…Based on the dependence of the measured signal on the modulation frequency of the THz source, this previous study identified that this interaction has a thermal origin. As such, this incoherent response was reported to be much slower than the picoseconds time response indicative of an EO mechanism such as that reported in [19]. Nevertheless, the specific mechanism of this thermal response was not established unequivocally in this previous study.…”

“…In the latter case, synchronization of the optical probe with the QCL has been accomplished by phase-seeding the QCL emission with THz pulses generated both externally [15] and internally [16]t o the QCL cavity, as well as by electrical stabilization of the QCL using a phase-locked loop [17]. The use of these coherent EO sampling schemes has led to the study of active modelocking [18], gain clamping [15], and more generally, the sampling coherence [19] of THz QCLs.…”

Narrow bandwidth injection seeding of a THz quantum cascade laser

“…After this time the gain is more or less saturated by the field in the cavity and no further amplification occurs. For both seed frequencies the output of the QCL was found to saturate with the amplitude of the seed pulse, which implies the majority of the QCL emission is phase locked to the seed [5]. Fig.…”