Threshold Power for Parametric Nonlinear Interactions
Posted on 2006-07-30 (revised on 2006-09-03) as a part of the Photonics Spotlight (available as e-mail newsletter!)
Permanent link: https://www.rp-photonics.com/spotlight_2006_07_30.html
Author: Dr. Rüdiger Paschotta, RP Photonics Consulting GmbH
Abstract: The Photonics Spotlight presents another physics conundrum, this time in the area of nonlinear optics. Essentially the question is why parametric oscillation involves a threshold pump power, while frequency doubling does not, even though both processes appear to be time-reversed versions of each other.
Ref.: encyclopedia articles on parametric amplification, optical parametric oscillators, frequency doubling, etc.
Degenerate parametric oscillation is sometimes described as essentially a time-reversed version of the process of singly resonant frequency doubling, i.e. frequency doubling with resonant enhancement of the pump wave. While parametric oscillation involves the “splitting” of high-energy pump photons into pairs of lower-energy photons, the opposite occurs in a frequency doubler.
It is striking, however, that parametric oscillation occurs only for pump powers above a certain threshold pump power (similar to a laser threshold), while frequency doublers do not exhibit such a threshold (even though their efficiency is poor for low pump powers). This apparent mystery was brought up years ago in a Ph. D. viva. I am not sure whether the originator of the question knew the answer (the Ph. D. candidate didn't!), but the question is interesting anyway. For now I leave this as another conundrum for my readers, and may post the correct answer later on in the Photonics Spotlight.
Note that the resolution of this issue has been published on 2006-09-03.
This article is a posting of the Photonics Spotlight, authored by Dr. Rüdiger Paschotta. You may link to this page and cite it, because its location is permanent. See also the RP Photonics Encyclopedia.
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