Utjecaj vanjskog koherentnog zračenja na rubidijeve atome u magnetno-optičkoj stupici

doctoral thesis

• Title (english): Influence of the external coherent radiation on rubidium atoms in a magneto-optical trap
• Author: Gordana Kregar
• Mentor: Ticijana Ban (mentor)
• Committee member: Damir Veža (predsjednik povjerenstva)
• Committee member: Ticijana Ban (član povjerenstva)
• Committee member: Hrvoje Buljan (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; (Department of Physics); Zagreb
• Defense date and country: 2014-10-29, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Physics
• Universal decimal classification (UDC): 53 - Physics

Abstract

U ovom doktorskom radu realizirana je magnetno-optička stupica (MOT) rubidijevih atoma, koja predstavlja jednu od tehnika laserskog hlađenja i zarobljavanja atoma. Navedena tehnika detaljno je opisana u radu, a njenom implementacijom u Laboratorij za femtosekundnu lasersku spektroskopiju na Institutu za fiziku, otvoreno je novo područje istraživanja koje se bazira na laserskom hlađenju i zarobljavanju atoma. Dobiveni hladni oblak sadrži ~ 109 atoma 87^Rb, koji se nalaze u stanju F_g = 2, u volumenu od ~ 3 mm3, gustoće ~ 1011 atoma/cm3 u tipičnim radnim uvjetima MOT-a. Uz karakterizaciju oblaka, opisan je teorijski model, baziran na Dopplerovoj sili hlađenja primjenjenoj na realni atomski sistem rubidija 87. Fokus samog rada stavlja se na istraživanje utjecaja vanjske sile u obliku koherentnog kontinuiranog (cw) i pulsnog (femtosekundnog) zračenja na dinamiku hladnih rubidijevih atoma. Uvedena je nova tehnika opažanja oscilacija centra mase oblaka koje nastaju kao rezultat djelovanja cw lasera, kojom su određeni osnovni parametri stupice: konstanta opruge, koeficijent gušenja i temperatura atoma. Određen je po prvi puta efektivni intenzitet saturacije 87^Rb D1 (F_g = 2 → F_e = 2) prijelaza za različite uvjete rada stupice. Interakcija hladnih rubidijevih atoma s frekventnim češljem razmatrana je u tri razlicite eksperimentalne konfiguracije, gdje je za svaku izmjeren LIF iz oblaka te radijativna sila, što je potom uspoređeno s teorijskim modelom, izvedenim prema optičkim Blochovim jednadžbama (OBE) za atomski sustav s dva energijska nivoa koji interagira s nizom fs pulseva.

Abstract (english)

In this dissertation a cloud of cold rubidium atoms confined in a magnetooptical trap (MOT) has been realized. The laser cooling and trapping technique was implemented in the Laboratory for femtosecond frequency comb spectroscopy at Institute of Physics for the first time, so this work opens a new area of research. The cloud of cold atoms, containing ~ 10^9 87^Rb, F_g = 2, in volume ~ 3 mm3, density of ~ 1011 atom/cm3 in typical MOT operating conditions was obtained. Detailed characterization of the cloud has been done and the Doppler model for the real atomic system of rubidium 87 atoms was applied to describe the radiative force. The main focus of this work is investigation of the coherent continuous (cw) or pulsed (femtosecond) radiation effects on rubidium atoms in MOT. Atomic motion in the trap can be described with a damped harmonic oscillator model. A new technique for monitoring cold cloud center of mass oscillations induced by cw laser, tuned to rubidium resonant transition has been introduced. With this method the basic trap parameters, such are spring constant, damping coefficient and atom temperature are determined. For various trap working conditions an effective saturation intensity of 87^Rb D1 (F_g = 2 → F_e = 2) transition is, for the first time, determined through experimentally and theoretically investigated rubidium excited F_e = 2 state population depending on the probe beam intensity. Also, the radiative force of the probe D1 laser on cold cloud is measured and theoretically modelled. Interaction of cold rubidium cloud with femtosecond (fs) pulses has been studied in three different experimental configurations; interaction of cold atoms with single fs train of pulses, with two in-phase counterpropagating fs pulses and with two out-of-phase counterpropagating fs pulses. In all three described geometries the LIF signal and radiative force are experimentally determined and compared with theoretical model, based on optical Bloch equations (OBE) for two energy level atom.

• Keywords: magnetno-optička stupica; lasersko hlađenje i zarobljavanje atoma; radijativna sila; konstanta opruge i koeficijent gušenja stupice; dinamika hladnih atoma; oscilacije centra mase oblaka; efektivni saturacijski intenzitet; femtosekundni frekventni češalj
• Keywords (english): magneto-optical trap; laser cooling and trapping of atoms; radiative force; trap spring constant and damping coefficient; cold atoms dynamics; cold cloud centre of mass oscillations; effective saturation intensity; femtosecond frequency comb
• Language: croatian
• URN:NBN: urn:nbn:hr:217:850676
• Study programme: Title: Physics; Study programme type: university; Study level: postgraduate; Academic / professional title: doktor/doktorica znanosti, područje prirodnih znanosti, polje fizika (doktor/doktorica znanosti, područje prirodnih znanosti, polje fizika)
• Type of resource: Text
• Extent: 153 str.
• File origin: Born digital
• Access conditions: Open access
• Created on: 2017-08-25 07:40:46