Laser Oscillation

Peter W. Milonni

It is well known that laser oscillation is initiated by spontaneous radiation ‘‘noise.’’ Evidence for this is often based on the complete theory of laser oscillation, including the quantization of the electromagnetic field. In this article, the buildup of laser oscillation from quantum noise is demonstrated using the most elementary classical equation describing the amplification of laser intensity.

Kōichi Shimoda

Kōichi Shimoda

F. B. Baalbergen, Iman Esmaeil Zadeh, M. J. A. de Dood

We demonstrate laser-induced relaxation oscillations in superconducting nanowire single-photon detectors (SNSPDs). These oscillations appear when a voltage-biased Nb Ti N nanobridge detector is illuminated with intense pulsed-laser light at a repetition rate of approximately 19 MHz . They differ from the well-known relaxation oscillations by a stepwise increase in frequency and phase locking of the oscillations to the laser pulses. We create a model that incorporates electrical feedback and excludes thermal effects to simulate and explain the origin of the observed laser-induced relaxation oscillations. Qualitative agreement to the experiment is achieved using realistic values for the parameters in the model.

Noriaki Horiuchi

Hui W. Cao

A photon, unlike an electron, can stimulate an excited atom to emit a second photon into the same electromagnetic mode. This stimulated emission process is the foundation for light amplification and oscillation (i.e., self-generation). Initially, the term LASER referred to Light Amplification by Stimulated Emission of Radiation. Nowadays laser often means Light Oscillation by Stimulated Emission, which should literally be called "€œLOSER"€ instead of "€œLASER." To distinguish the above two devices, the former is called a laser amplifier, the latter a laser oscillator (Siegman 1986). Laser oscillation occurs when the photon generation rate exceeds the photon loss rate in a system. If gain saturation were absent, the photon number in a laser oscillator would diverge in time. In other words, the rate equation for the photon number would acquire an unstable solution above the oscillation threshold. In reality, gain saturation reduces the photon generation rate to the photon loss rate so that the number of photons in the oscillator remains at a finite value.