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Physical Review Letters

Microlaser: A laser with One Atom in an Optical Resonator

Kyungwon An, James Childs, Ramachandra Rao Dasari, Michael S. Feld

Published Dec 19, 1994• 283 citations
Publisher

Abstract

We have demonstrated laser oscillation with one atom in an optical resonator. In our experiment a beam of $^{138}\mathrm{Ba}$ atoms traverses a single-mode cavity with a finesse of 8 \ifmmode\times\else\texttimes\fi{} ${10}^{5}$. The atoms are excited by a $\ensuremath{\pi}$ pulse from the $^{1}S_{0}$ ground state to the $^{3}P_{1}(m=0)$ excited state before they enter the cavity. Laser oscillation at 791 nm ($^{3}P_{1}\ensuremath{\rightarrow}^{1}S_{0}$) has been observed, with the mean number of atoms inside the mode ranging from 0.1 to 1.0, resulting in the mean number of photons inside the cavity changing from 0.14 to 11. The results are in good agreement with a fully quantized micromaser theory adapted to our experiment.

DOI
10.1103/physrevlett.73.3375

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Role of standing-wave mode structure in microlaser emission

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In the recently developed microlaser, a single two-level atom interacts with a single mode of the optical resonator to generate coherent radiation. The resonator mode is in the form of a standing wave. We present an analysis of the standing-wave features, based on an approximate solution of the fully quantized microlaser equations. The result explains the rapid increase in the observed signal when the average number of atoms in the cavity is of the order of 1.

Physical Review A•Aug 1, 1995•15 citations
We have demonstrated laser oscillation with one atom in an optical resonator. In our experiment a beam of 138Ba^{138}\mathrm{Ba}138Ba atoms traverses a single-mode cavity with a finesse of 8 \ifmmode\times\else\texttimes\fi{} 105{10}^{5}105. The atoms are excited by a \ensuremathπ\ensuremath{\pi}\ensuremathπ pulse from the 1S0^{1}S_{0}1S0​ ground state to the 3P1(m=0)^{3}P_{1}(m=0)3P1​(m=0) excited state before they enter the cavity. Laser oscillation at 791 nm (3P1\ensuremath→1S0^{3}P_{1}\ensuremath{\rightarrow}^{1}S_{0}3P1​\ensuremath→1S0​) has been observed, with the mean number of atoms inside the mode ranging from 0.1 to 1.0, resulting in the mean number of photons inside the cavity changing from 0.14 to 11. The results are in good agreement with a fully quantized micromaser theory adapted to our experiment.
We have achieved the first realization of a single atom microlaser, a laser oscillator with only one atom in an optical resonator. In the experiment a beam of two-level barium atoms traverses an ultrahigh Q single-mode cavity. The atoms are inverted by a (pi) -pulse field before they enter the cavity. Laser oscillation ((lambda) equals 791 nm) has been observed, with the mean number of atoms inside the mode <N> as small as 0.1, resulting in the mean number of photons in the mode <N> or 0.14. To understand the results quantitatively we used a fully-quantized one-atom microlaser theory adapted from its counterpart micromaser theory. The present theory was found to be in good agreement with the data for small <N> and <n>. Discrepancy between experiment and theory was observed for <n> very much greater than 1 and <N> approximately equal to 1. This discrepancy may be explained by the standing-wave nature of the cavity mode, in combination with the saturation effect occurring at large cavity photon number, as well as by the breakdown of single-atom interaction assumption in the theory for <N> greater than or equal to 1.
The single-atom microlaser is one and the only type of single atom lasers realized experimentally so far. The gain medium is a beam of excited, non-interacting two-level atoms (/spl lambda/=791 nm, /sup 3/P/sup 1//spl rarr//sup 1/S/sub 0/ transition of /sup 138/Ba) entering an ultra-low loss resonator one at a time. This laser device utilizes the coherent atom-cavity interaction, often referred to as quantized Rabi oscillation, as the light amplification method, With the mean atom number about unity, tens of photons could be stored inside the cavity. The laser oscillation persisted with the mean number of atoms in the cavity well below unity.
Summary form only given. We have recently developed the first working single-atom microlaser in which coherent light is generated by means of the interaction of a single two-level atom with a single mode of the radiation field. The photon generation process follows the Jaynes-Cummings model, and photon buildup is initiated by vacuum Rabi oscillations, not by spontaneous emission as in conventional lasers. We measured the mean photon number in the cavity (n) as a function of the average number of atoms present there . Laser oscillation was observed with as small as 0.1, resulting in (n) of 0.1.
We report the observation of multiple laser thresholds in the many-atom cavity QED microlaser. Traveling-wave coupling and a supersonic atom beam are used to create a well-defined atom-cavity interaction. Multiple thresholds are observed as jumps in photon number due to oscillatory gain. Although the number of intracavity atoms is large, up to $N\ensuremath{\sim}{10}^{3}$, the dynamics of the microlaser agree with a single-atom theory. This agreement is supported by quantum trajectory simulations of a many-atom microlaser and a semiclassical microlaser theory. We discuss the relation of the microlaser with the micromaser and conventional lasers.