Nonlinear effects in the interaction between the laser and the alkai vapor

Vdović, Silvije (2010) Nonlinear effects in the interaction between the laser and the alkai vapor. Doctoral thesis, Faculty of Science > Department of Physics.

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Abstract

This thesis examines nonlinear interaction between the alkali vapor and different laser sources in various conditions. Interaction between cw lasers and rubidium atomic vapor in the V coupling scheme produces electromagnetically induced transparency, where the main contibution to the induced transparency comes from nonlinear saturation effects on the strongly coupled transition. By comparing the theoretical model and experimental results it is shown that part of the induced transparency comes from coherences induced between the uncoupled transitions. Interaction between the femtosecond (fs) pulses and resonant rubidium atomic vapor is investigated using frequency-resolved optical gating (FROG) technique. Propagation of the fs pulses in the optically thin medium results in formation of 0-π pulses which have strong modulation of the electric field amplitude on a time scale of several ps. Since it is impossible to cover the whole time evolution of the 0-π pulse, the FROG reconstruction process can never be accurate enough. Propagation of nearly-resonant pulses through the optically thick rubidium vapor results in conical emission due to the self-focusing of the pulse in time domain and self-phase modulation in frequency domain. Using the adiabatic following approximation, it is shown that the physical processes depend on the sign of detuning of pulse wavelength from the rubidium resonance lines. The pulse electric field phase in both domains, retrieved from the FROG measurements, shows different behavior with respect to the sign of the pulse detuning. Degenerate four-wave mixing (DFWM) of femtosecond pulses in sodium vapor was performed in BOXCARS geometry. When on three-photon atomic resonance, transient grating signal appeared on the frequency of the third harmonic of fundamental frequency at negative delay times with modulations whose period corresponds to the energy difference between the coherently excited upper state fine stucture levels. In positive time delays signal appears at the fundamental frequency and there is no signal at third harmonic frequency. This is explained by destructive interference between the fundamental field and the field at the frequency of third harmonic. The amplitudes of modulations at negative time delays have exponential time dependence determined by the coherence relaxation time.

Item Type: Thesis (Doctoral thesis)
Keywords: electromagnetically induced transparency ; frequency-resolved optical gating ; femtosecond pulse ; degenerate four-wave mixing ; conical emission ; self-phase modulation ; self-focusing ; quantum beats ; third-harmonic generation
Supervisor: Pichler, Goran
Date: 15 July 2010
Number of Pages: 153
Subjects: NATURAL SCIENCES > Physics
Divisions: Faculty of Science > Department of Physics
Depositing User: Gordana Stubičan Ladešić
Date Deposited: 22 Dec 2013 21:58
Last Modified: 22 Dec 2013 21:58
URI: http://digre.pmf.unizg.hr/id/eprint/53

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