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Injection Laser Threshold from the Standpoint of Collective Resonance

Nikita Yu. Gordeev, Leonid Ya. Karachinsky, V. I. Kopchatov, P. S. Kop’ev, I. I. Novikov

Published Jun 23, 2000• 0 citations
OpenAlex

Abstract

Mechanism of laser threshold is considered in terms of superradiance. Presence of short Coherent pulses has been demonstrated below at and above laser threshold in wide temperatwe range. Existence of positive feedback leads to SR pulse becomes longer. Luminescence lineshape above threshold has a complex structure but is well described using the theory of collective recombination. Spectral investigations at low and room temperatwe. as well as time coherence measurements at RT allow estimating the characteiistic time of superradiance pulse in these two modes. The maximum duration of the pulse has been found as low as 300 fs at RT and 70 fs at 77 K.

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arXiv:1807.11775•Optics Express•Apr 19, 2019•42 citations
Mechanism of laser threshold is considered in terms of superradiance. Presence of short Coherent pulses has been demonstrated below at and above laser threshold in wide temperatwe range. Existence of positive feedback leads to SR pulse becomes longer. Luminescence lineshape above threshold has a complex structure but is well described using the theory of collective recombination. Spectral investigations at low and room temperatwe. as well as time coherence measurements at RT allow estimating the characteiistic time of superradiance pulse in these two modes. The maximum duration of the pulse has been found as low as 300 fs at RT and 70 fs at 77 K.
Peculiarities of the implementation of a superradiant generation mode in a laser with a distributed feedback of the waves and an inhomogeneously broadened spectral line of the active medium are investigated. Based on a numerical solution of the semiclassical Maxwell-Bloch equations for the amplitudes of counterpropagating electromagnetic waves, polarization, and inversion of a two-level medium population, it is shown that a sequence of coherent high-power pulses is generated by the Bragg structure in a wide range of the laser parameters as a result of the selected mode and the cw pumping.
Since Karras et al. published a paper on the observation of optical cooperative emissions from copper vapor,1 no other convincing experimental evidence has been reported on this puzzling phenomenon. We reported an observation of a similar behavior of the stimulated emission from the copper-vapor laser in the context of Dicke superradiance.2 Subsequently we have carried out a detailed experimental investigation on this pulsing phenomenon in a transverse-discharge copper-vapor laser system. By means of a precision spectral analysis we can identify two principal mechanisms which are responsible for the multiple-pulsing phenomenon in a high-gain condition: (1) the superimposition of a few pulses corresponding to different regions of the spectrum of the laser line, and (2) superradiant ringing due to the coherent collective effect. The conditions in which one or the other of the two mechanisms is manifested are subtle and are not completely understood as yet. But the characteristics of the optical pulses resulting from each mechanism are quite distinct. We describe the difference between the two mechanisms and present the experimental results that exhibit an interesting spectral behavior of the laser pulses in each case.
Superradiance (SR), or cooperative spontaneous emission, has been predicted by R. Dicke before the invention of the laser. During the last few years one can see a renaissance of both experimental and theoretical studies of the superradiant phase transition in a variety of media, ranging from quantum dots and Bose condensates through to black holes. Until recently, despite of many years of research, SR has been considered as a phenomenon of pure scientific interest without obvious potential applications. However, recent investigations of the femtosecond SR emission generation from semiconductors have opened up some practical opportunities for the exploitation of this quantum optics phenomenon. Here we present a brief review of some features, advantages and potential applications of the SR generation from semiconductor laser structures
Singly ionized nitrogen molecules in ambient air pumped by 800 nm femtosecond laser give rise to superradiant emission. Here, we study this superradiance by injecting a pair of resonant seeding pulses at different intensity ratios inside the nitrogen gas plasma. Strong modulation of the 391.4 nm superradiant emission with a period of 1.3 fs is observed when the delay between the two seeding pulses is finely tuned. The modulation contrast is increased and then decreased with the delay time when the second seed pulse is stronger than the first one, and the maximum modulation contrast occurs at longer delay time when the second seeding pulse is stronger. This reveals the increase of the macroscopic polarization with time after the seeding pulse. Moreover, these observations provide a new level of control on the "air lasing" based on nitrogen ions, which can find potential applications in optical remote sensing.