Abstract
We present a high-speed asynchronous optical sampling system, based on two different Kerr-lens mode-locked lasers with a GHz repetition rate: An Yb:KYW oscillator and a Ti:sapphire oscillator are synchronized in a master-slave configuration at a repetition rate offset of a few kHz. This system enables two-colour pump-probe measurements with resulting noise floors below 10⁻⁶ at a data aquisition time of 5 seconds. The measured temporal resolution within the 1 ns time window is below 350 fs, including a timing jitter of less than 50 fs. The system is applied to investigate zone-folded coherent acoustic phonons in two different semiconductor superlattices in transmission geometry at a probe wavelength far below the bandgap of the superlattice constituents. The lifetime of the phonon modes with a zero wave vector and frequencies in the range from 100 GHz to 500 GHz are measured at room temperature and compared with previous work.
Highlights
Ultrafast laser spectroscopy systems have drawn great attention during the last decades due to their versatile applications in solid-state physics, biology and medicine
Modern spectroscopy techniques rely on ultrashort laser pulses and offer femtosecond temporal resolution
Beam size modulation and beam poynting from mechanical delay stages influence the measurement. These limitations can be overcome by implementing high-speed asynchronous optical sampling (ASOPS), where the repetition rate of two gigahertz lasers is synchronized at an offset of several kHz [4]
Summary
Ultrafast laser spectroscopy systems have drawn great attention during the last decades due to their versatile applications in solid-state physics, biology and medicine. Modern spectroscopy techniques rely on ultrashort laser pulses and offer femtosecond temporal resolution This enables studying the dynamics of fundamental ultrafast excitations in semiconductors like charge carriers, phonons, plasmons, excitons and many more [1, 2]. Beam size modulation and beam poynting from mechanical delay stages influence the measurement These limitations can be overcome by implementing high-speed asynchronous optical sampling (ASOPS), where the repetition rate of two gigahertz lasers is synchronized at an offset of several kHz [4]. A huge progress in the development of femtosecond solid state lasers (SSLs) with GHz repetition rates, based on the ytterbium doped double tungstates Yb:KYW and Yb:KGW, was noticeable [14,15,16,17,18] These lasers are cost-efficient and compact, as they are pumped with high-power semiconductor laser diodes. The resulting lifetimes of the folded zone-center modes are discussed
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