#### Pregled bibliografske jedinice broj: 404174

## Recent development of direct femtosecond laser frequency comb spectroscopy

Recent development of direct femtosecond laser frequency comb spectroscopy

*// Modern Trends in Mathematics and Physics*/ Prof. Dr. Savch Tinchev (ur.).

Sofia: Heron Press, 2009. str. 31-38 (pozvano predavanje, nije recenziran, cjeloviti rad (in extenso), znanstveni)

**Naslov**

Recent development of direct femtosecond laser frequency comb spectroscopy

**Autori**

Pichler, Goran ; Aumiler, Damir ; Ban, Ticijana ; Vujičić, Nataša ; Vdović, Silvije ; Skenderović, Hrvoje

**Vrsta, podvrsta i kategorija rada**

Radovi u zbornicima skupova, cjeloviti rad (in extenso), znanstveni

**Izvornik**

Modern Trends in Mathematics and Physics
/ Prof. Dr. Savch Tinchev - Sofia : Heron Press, 2009, 31-38

**ISBN**

978-954-580-264-5

**Skup**

Modern Trends in Mathematics and Physics

**Mjesto i datum**

Varna, Bugarska, 5-10.9.2008

**Vrsta sudjelovanja**

Pozvano predavanje

**Vrsta recenzije**

Nije recenziran

**Ključne riječi**

Femtosekundna spektroskopija

(Femtosecond spectroscopy)

**Sažetak**

We shall discuss the direct observation of the velocity-selective optical pumping of the Rb ground state hyperfine levels induced by femtosecond pulse-train excitation. A modified direct frequency comb spectroscopy based on the fixed frequency comb and a weak cw scanning probe laser was developed and the experimental results are compared with theoretical evaluations in the context of the density matrix formalism. A mode-locked femtosecond laser is used to physically map the laser frequency comb into the velocity comb of the excited Rb atoms at room temperature. Upon resonant excitation by discrete optical frequencies the velocity distribution of the excited Rb atoms shows comblike structure. Simultaneously, velocity-selective population transfer occurs between ground-state hyperfine levels. This direct observation of the velocity-selective optical pumping of the ground state hyperfine levels induced by the femtosecond (fs) laser oscillator was also tested experimentally and theoretically in the case Cs D2 (852 nm) and Cs D1 (894 nm) cesium line. The frequency comb excitation changes the usual Doppler absorption profile into a specific periodic, comblike structure. Coherent control of atomic interactions with photons from the pulse-train caused accumulation effects of atomic coherences and populations. We further investigated the coherence accumulation effects in Rb atoms excited by a train of femtosecond pulses. The effect of the pulse train excitation on the cw probe laser transmission was investigated in dependence on the probe laser power. Results show that accumulation of population and coherence can be effectively reduced and eventually destroyed by increasing the cw laser intensity. A strong cw laser can therefore serve as a switch from the pulse-train to pulse-by-pulse type of interaction of Rb atoms with the fs laser. Our extended model well describes these findings. We introduced a new and simple method for determination of the absolute frequencies of comb lines within the optical frequency comb spectrum. A combined experimental and theoretical approach is presented which utilizes the effect of velocity selective optical pumping of hyperfine lines induced by the resonant frequency comb excitation. The laser pulse repetition frequency and carrier envelope offset are physically mapped onto the 87Rb ground state hyperfine level population velocity distributions. An iterative analytic solution to the optical Bloch equations describing the resonant pulse-train excitation of 4-level 87Rb atoms is found. Theoretical results are used to fit the observed mapping and obtain the parameters of the frequency comb, thus providing a practical algorithm which can be used in real-time measurements. Finally we added appropriate atomic Rb filter cell at different temperatures, which modifies amplitudes and phases of the frequency comb lines of the femtosecond laser. Therefore, the direct observation of the velocity selective optical pumping of the 87, 85Rb ground state 5 2S1/2 hyperfine levels induced by the modified femtosecond (fs) pulse train will be changed. A weak cw scanning probe laser will show amplitude changes of the modified comb lines when transmitted through Rb filter cell. Phase changes of the comb lines will be visible in the time domain behavior of the cw probe laser. We hope to apply atomic filter experiments in the selective pumping of the ultracold rubidium cloud in the photoassociation experiments.

**Izvorni jezik**

Engleski

**Znanstvena područja**

Fizika

**Napomena**

Ovaj rad će uskoro izaći kao poseban broj znastvenog časopisa u Bugarskoj

**POVEZANOST RADA**

**Projekt / tema**

035-0352851-2857 - Femtosekundna laserska fizika atoma i molekula (Goran Pichler, )

**Ustanove**

Institut za fiziku, Zagreb