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Laser light takes on terahertz territory

23 Jun 2014

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Professor Masayuki Katsuragawa

Thanks to the innovations in powerful lasers, optical fibres, and peripheral technology, it has eased and widened the use of telecommunications based on the transmission of 10GHz pulses of light worldwide.

Notably, the three most important properties of lasers for telecommunications are high power, single frequency, and ultra-short pulse width. But what innovations lie ahead? The answer to this question can be found in the research being conducted by Professor Masayuki Katsuragawa at the Department of Applied Physics and Chemistry, University of Electro-Communications.

"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 realisation 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."

Here, the new axis refers to ultra high-repetition-rate trains of monocycle pulses with precise control of the phase of the laser light pulses. Recently, Katsuragawa and his colleagues have reported on the realisation of ultrashort pulse trains of 1.8fs in duration and repetition frequency of 125THz by stimulated Raman scattering (SRSs) 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."

 laser light sources producing pulses at terahertz repetition-rate frequencies

Recently, the UEC team has produced higher order series of stimulated Raman scattering 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.

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