Spectral narrowing induced by discrete frequency fluctuations

A.L.J. Burgmans, Martin F. H. Schuurmans

Shuo Zhang, Signe Louise Seidelin, Rodolphe Le Targat +3 more

The possibility of generating a narrow spectral hole in a rare-earth doped crystal opens the gateway to a variety of applications, one of which is the realization of an ultrastable laser. As this is achieved by locking in a prestabilized laser to the narrow hole, a prerequisite is the elimination of frequency fluctuations of the spectral hole. One potential source of such fluctuations can arise from temperature instabilities. However, when the crystal is surrounded by a buffer gas subject to the same temperature as the crystal, the effect of temperature-induced pressure changes may be used to counterbalance the direct effect of temperature fluctuations. For a particular pressure, it is indeed possible to identify a temperature for which the spectral hole resonant frequency is independent of the first-order thermal fluctuations. Here, we measure frequency shifts as a function of temperature for different values of the pressure of the surrounding buffer gas, and identify the ``magic'' environment within which the spectral hole is largely insensitive to temperature.

John E. Beetar, Michael Chini

Abraham G. Kofman

Electromagnetically induced transparency (EIT) with chaotic field is considered for the constructive-interference case ( i.e. ,when the material transition is much narrower than the coupled one). The field intensity fluctuations are shown to induce a narrow peak at the material frequency, in addition to the familiar Autler-Towns doublet. The dependence of the fluctuation-induced peak on the field bandwidth ν is obtained analytically and numerically. EIT is shown to increase with ν for sufficiently small ν.

P. A. Folkes

We report the observation of correlated photon fluctuations over a narrow range of current at threshold of an interband cascade laser using single-detector photon noise measurements. The correlated photon noise is manifested by large fluctuations in the low-frequency photon noise spectral density at certain discrete frequencies which are sensitive to the laser gain characteristics. We observe the concurrent emergence and growth of the lasing mode over the same current range indicating that the correlated photon noise provides evidence of the occurrence of a change in the photon fluctuation statistics and the onset of first-order coherence in the laser emission at threshold.

V. Hizhnyakov, Inna Rebane