Observation of instabilities due to mirrorless four-wave mixing oscillation in sodium

Injection seeding has proven to be a practical method of controlling the spectral output of a laser in an efficient and reliable manner. To achieve satisfactory injection seeding performance, a sufficiently large seed must be employed. To characterize the required seed, an injection seeding theory is developed here which establishes two interrelated concepts, threshold for injection seeding and spectral purity of the laser output. Rather than utilizing numerical techniques to solve the differential equations, closed-form expressions for the threshold are developed for not only common continuous wave injection seeding but pulsed injection seeding as well. In addition, effects of alignment of the seed to the resonator, both in position and angle, and effects of frequency mismatch, or difference between the seed and the resonant frequencies of the resonator, are taken into account. Expressions for the threshold utilize readily measurable experimental parameters. Spectral purity of the laser output and its consequences on the required seed power or energy are also explored. >

Injection seeding. I. Theory

Degenerate conical emissions that appear in laser-pumped atomic sodium have been reported. The cones appear for both single- and double-pump geometries. The nonlinear medium is a small, high-density sodium-seeded flame. Earlier work that relates the cones to the process of degenerate phase conjugation is extended. The analysis for the single-pump phenomenon is formally related to amplified spontaneous emission. The double-pump case is analogous to a distributed-feedback laser. Theory and experiment are presented and discussed.

Degenerate conical emissions in atomic-sodium vapor

Possibilities for ultrasensitive mass spectrometry based on two-photon, sub-Doppler resonance ionization

Atoms can scatter light and they can also amplify it by stimulated emission. 
From this simple starting point, we examine the possibility of realizing a random laser in a cloud of laser-cooled atoms. The answer is not obvious as both processes (elastic scattering and stimulated emission) seem to exclude one another: pumping atoms to make them behave as amplifier reduces drastically their scattering cross-section. However, we show that even the simplest atom model allows the efficient combination of gain and scattering. Moreover, supplementary degrees of freedom that atoms offer allow the use of several gain mechanisms, depending on the pumping scheme. We thus first study these different gain mechanisms and show experimentally that they can induce (standard) lasing. We then present how the constraint of combining scattering and gain can be quantified, which leads to an evaluation of the random laser threshold. The results are promising and we draw some prospects for a practical realization of a random laser with cold atoms.

Towards a random laser with cold atoms

Flashlamp pumped tunable dye laser of ultra-narrow bandwidth

Degenerate four-wave mixing in sodium vapor is investigated using a flashlamp-pumped dye laser synchronized on a cw dye laser. At low atomic density, the reflectivity versus the pump intensity and the line shapes are in good agreement with theoretical predictions in the case of both plane waves and Gaussian beams. At high atomic density, reflectivities much higher than unity have been observed. The influence of the pump imbalance has been studied as well as the deformation of the wave front of the conjugated beam introduced by the pump beams. In the high-atomic-density case, the theoretical problem is more complex, and our experimental results exhibit only qualitative agreement with theory.

Degenerate four-wave mixing in sodium vapor in the Rabi regime

Nous presentons dans cet article les performances d'un laser a colorant pompe par flash lorsque l'on injecte dans la cavite du laser a colorant un faisceau continu de grande purete spectrale (Δv < 20 MHz). Nos experiences sont realisees en utilisant la sulforhodamine B comme colorant, le faisceau continu provenant d'un laser a krypton (raie a 6 471 A). La repartition spectrale du faisceau laser en impulsion depend de plusieurs parametres dont nous etudions l'influence : tension appliquee aux flashs, puissance injectee dans la cavite, accord de la cavite. Dans les meilleures conditions de fonctionnement, nous obtenons une puissance de 100 watts pendant 200 ns dans une bande spectrale inferieure a 25 MHz, la distance entre le centre de cette bande et la frequence injectee est inferieure a 15 MHz. On remarque en outre que 5 mW de puissance injectee suffisent pour atteindre ces meilleures performances.

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F. Trehin

Papers

Flashlamp pumped tunable dye laser of ultra-narrow bandwidth

Degenerate four-wave mixing in sodium vapor in the Rabi regime

Synchronisation d'un laser à colorant en impulsions par injection d'un faisceau laser continu de grande pureté spectrale

Pulse shortening in degenerate four wave mixing in atomic sodium vapor