Professor Masayuki Katsuragawa from the Department of Applied Physics and Chemistry at the University of Electro-Communications (UEC; Tokyo, Japan) has developed a new method to produce ultrashort-pulse light. "My research is focused on the manipulation of light-matter interaction for producing ultra-short pulses of laser light," says Katsuragawa. "Our recent experiments on adiabatic stimulated Raman scattering in parahydrogen show potential for the realization of laser light sources producing pulses at terahertz repetition-rate frequencies. These ultra-short pulses offer a new 'axis' in the evolution of laser based optical science."
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Here, the new 'axis' refers to ultrahigh-repetition-rate trains of monocycle pulses (http://www.laserfocusworld.com/articles/print/volume-47/issue-8/features/photonic-frontiers-single-cycle-pulses-spectral-broadening-advances-quest-for-single-cycle-pulses.html) with precise control of the phase of the laser light pulses. Advances in the performance of powerful lasers, optical fibers, and peripheral technology have played a pivotal role in the proliferation of global telecommunications based on the transmission of 10 GHz pulses of light, says UEC. Notably, they say that the three most important properties of lasers for telecommunications are high power, single frequency, and ultrashort pulse width.
Recently, Katsuragawa and his colleagues demonstrated ultrashort pulse trains of 1.8 fs in duration with a repetition frequency of 125 THz by stimulated Raman scattering (SRS) produced in parahydrogen. "The critical point in these experiments was driving Raman coherence adiabatically, that is, without dissipation," explains Katsuragawa. "We achieved this by developing an injection-locked laser capable of emitting arbitrary pairs of two frequencies to irradiate the hydrogen gas, in order to control two photon detuning from the Raman resonance."
Recently, the UEC team produced higher-order series of SRS using two driving lasers by the introduction of a second harmonic in one of the lasers. The resulting emission referred to as a 'Raman comb' covered an octave spectrum range from the infrared to the ultraviolet.
"I am confident that our research has laid the foundations for the development of practical systems for the generation of trains of monocycle pulses with total control of the phase," says Katsuragawa.
