RESUMO
We report the electrical conductivity of laser-produced warm dense aluminum plasmas measured using single-shot ultrafast terahertz (THz) frequency spectroscopy. In contrast with experiments performed at optical frequencies, measurements based upon THz probe reflectivity directly determine a quasi-dc electrical conductivity, and therefore the analysis does not require a free-electron Drude model based extrapolation to recover the near zero frequency conductivity. In fact, our experimental results indicate that the Drude model breaks down for warm (>0.6 eV), moderate-dense (<1.6 g/cm(3)) aluminum at THz frequencies. A calculation of THz reflectivity over a non-Fresnel boundary in dense plasmas is also presented.
RESUMO
A single-shot measurement of terahertz electromagnetic pulses is implemented using two-dimensional electro-optic imaging with dual echelon optics. The reported embodiment produces sequentially delayed multiprobe beamlets, routinely providing a time window of >10 ps with ~25 fs temporal step sizes. Because of its simplicity and robustness, the technique is ideally suited for real-time ultrashort relativistic electron bunch characterization.
RESUMO
By revisiting the theory of terahertz pulse detection schemes employing a chirped optical probe pulse, we address and resolve a conflict that exists in literature. In this report, we show that the equation governing the detected field depends upon the experimental scheme, and in the limit of small bandwidth, that this expression differs from the conventionally used equation through a phase factor. We experimentally verify this equation using a spectral in-line interferometry approach. We also briefly discuss the implications of our new equations for single-shot terahertz retrieval schemes.
RESUMO
An apparatus for recording broadband infrared absorption spectra from 2.2 to 2.7 microm with subpicosecond time resolution is described. It comprises a new subpicosecond IR continuum generator, based on stimulated electronic Raman scattering in Ba vapor, and a broadband, infrared-to-visible upconverter, utilizing alkali metal vapor.
