| dc.description.abstract | This dissertation is devoted to ultrafast waveform synthesis using coherent Raman sidebands with the assistance of pulse shapers based on acousto-optic programmable dispersive filter (AOPDF) or deformable mirror (DM). Ultrashort optical science has encompassed the realm of electronic and chemical processes taking place on the few femtosecond-to-attosecond timescale. Molecular modulation is a technique that has been developed to produce ultrafast pulses based on broadband coherent Raman scattering, which provides the required optical bandwidth. This technique is capable of producing a pulse whose duration can be shorter than one optical field cycle in the visible-UV range, providing a potential for non-sinusoidal field synthesis.
We produce the coherent Raman sidebands in a Raman-active crystal driven by two-color femtosecond laser pulses. With the assistance of a pulse shaper based on AOPDF, we report the phase control of the ultrabroad spectrum, aiming to synthesize non-sinusoidal waveforms. The setup allows for both coarse, manual phase adjustments and programmable fine-tuning of spectral phases. A flat spectral phase across these 5 frequency-separated sub-bands is achieved, which implies generation of isolated 2 to 3 optical-cycle pulses.
The energy of the ultrafast waveform produced in this setup is limited by the damage threshold of the pulse shaper. In order to obtain high energy ultrafast waveforms, we design a reflection scheme using spherical mirrors to combine the Raman sidebands. The sidebands and the driving pulses are refocused back to the Raman crystal and the relative spectral phases are retrieved from an interferogram based on nonlinear Raman interaction. Furthermore, using a DM to adjust the spectral phases, we demonstrate that our setup is capable of synthesizing ultrafast waveforms using the coherent Raman sidebands.
We explore an additional ultrashort pulse generation technique, theoretically. We investigate formation of resonant dispersive waves (RDW) in photonic crystal fibers (PCF). Our simulation shows that with an input of two pulses, or a broadband chirped pulse in a PCF, RDW could form a sufficiently short pulse in the UV region, which could be a new method to obtain the ultrashort UV pulse.
In addition to studying methods for production of ultrashort pulses, we explore areas where such pulses can be utilized. The field of ultrafast optics is highly interdisciplinary, with a wide range of applications. We report two experiments with femtosecond laser pulses: 1) we demonstrate a scheme which achieves sub-diffraction imaging of remote objects by using femtosecond laser filaments. The use of laser filaments for imaging is destined to have applications in many environments. Achieving super-resolution has become a scientific imperative for remote imaging of objects and scenes needing increased detail and has motivated the development of various laser-based techniques. 2) All-optical control device where the “gate” photon could switch a “source” light beam has been a long-standing goal in optics, especially in optical communication. In a transversely excited atmospheric (TEA) nitrogen laser setup, we trigger the nitrogen laser radiation with a femtosecond laser pulse switching a transverse discharge in air. Moreover, with two TEA lasers as a model, we demonstrate the swept gain scheme for remote sensing. | en |
