A Raman approach for arbitrary optical waveform synthesis ラマン光学過程を基礎とする任意波形光発生

博士論文

2010

This thesis describes a new approach for generating complex, user-specified ultrashortwaveforms (also known as “arbitrary optical waveforms”) in optical regime.The key idea is adiabatic driving of Raman process in a diatomic molecule (likeparahydrogen) with two monochromatic laser fields. When the frequency differenceof the laser fields is slightly detuned from the frequency of a selected rotationalRaman transition, and the intensities of the two driving lasers are strong enough;the molecules are prepared in a maximally coherent state. All molecules in theparahydrogen gas cell coherently oscillate in unison in this state and change itsrefractive index periodically. The oscillating molecular ensemble modulates thepropagating laser fields, thereby generating coaxial, discrete, mutually coherentradiation with a broad bandwidth. The generated high-power coherent radiationis also called as Raman sidebands.We experimentally demonstrate the generation of discrete, wide-frequencyspacing (typically THz), phase-coherent Raman sidebands by driving Raman processusing a dual-frequency injection laser system in parahydrogen medium atliquid nitrogen temperature (working transition: ν = 0, J = 2 ← ν = 0, J =0). By line-by-line manipulation of the spectral phases of Raman sidebands usinga specially designed spectral phase controller, we synthesized a train of Fouriertransform-limited pulses (17 fs at full width at half maximum) and arbitrary opticalwaveforms (especially rectangular- and triangular- type optical waveforms).The synthesized waveforms produced in this way have an unprecedented ultrahighrepetitionrate of ? 10 THz and a wide tunability regarding the carrier frequency.A new type of pulse characterization system based on spectral-interferometry ofdiscrete spectra is used for the measurement of generated waveforms. The trainsof user-specified shaped optical waveforms are stably produced at an ultrahighrepetition rate of 10.6229 THz, reminiscent of an ultrafast function generator.We also developed a new Raman source by using “parahydrogen filled kagomelatticetype photonic crystal fiber” for more efficient Raman sidebands generation.A broad Raman sidebands spectrum is generated for an incident energy nearly3000 times less compared to the free-space condition