Temporal Talbot effect in frequency-shifted feedback lasers

Orateur : Hugues GUILLET de CHATELLUS

Abstract : A frequency-shifted feedback (FSF) laser is a laser cavity closed on the +1 (or -1) diffraction order of an acousto-optics modulator (A OM). In the case of a linear cavity, each time a photon makes a roundtrip in the cavity, its frequency is increased (decreased) by a shift frequency equal to twice the AOM frequency. When seeded with a monochromatic laser, the output of the FSF laser consists in a frequency comb, which shows significant differences with conventional frequency combs generated in mode-locked lasers. First the frequency spacing of the comb is equal to the shift frequency, which can be adjusted and controlled electronically. Second, the phases of the modes of the optical comb are quadratic and the curvature of the parabola can be adjusted by the FSF cavity free spectral range and by the shift frequency. When these two frequencies are in the ratio of two integers, this leads to a temporal fractional Talbot effect : the output of the laser consists in a train of Fourier transform limited pulses at a repetition rate equal to the least common multiple of these two frequencies, leading to the possibility of ultrahigh repetition rates, limited only by the spectral bandwidth of the laser. We demonstrated experimentally the generation of 6 ps pulses from a 150 GHz bandwidth FSF laser, at a repetition rate tunable between 240 MHz and 37 GHz, by steps of 80 MHz. This possibility opens new perspectives for various applications where lasers with ultra-high repetition rates are required, from THz generation to ultrafast data processing systems and spectroscopy of metallic nanoparticles. Hugues Guillet de Chatellus is an alumnus from the Ecole Normale Supérieure in Lyon. He got his PhD from the University of Bordeaux I under the supervision of Dr. Eric Freysz. His field of research was the possibility to induce second-order non-linear properties in glasses by means of a thermal poling treatment, and to characterize and modify these properties with femtosecond laser pulses. He defended his thesis in july 2002. Between September 2002 and September 2004, he worked as a postdoc researcher for the Quantum Imaging Lab at Boston University, under the supervision of profs Sergienko, Saleh and Teich. He developed a technique to pole lithium niobate and to induce waveguides through electrical and chemical processes respectively for quantum information protocols. Back to France in October 2004, he spent a year at the LTSI in Saint-Etienne where he developed an imaging technique based on ultrafast Diffuse Optical Tomography. He was recruited by the CNRS in 2005 and join ed the LSP in Grenoble where he spent 5 years on the field of laser guide stars for astronomy. Since two years he focused on the physics and applications of frequency shifted feedback (FSF) lasers. http://imep-lahc.grenoble-inp.fr/ev....

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