报告题目：Wavelength Scaling in Nonlinear Pulse Compression and Extreme Frequency Conversion

报告人：Andrius Baltuska 院士

主持人：徐淮良教授

时间：2019-04-25   09:30

地点：理科大楼A510报告厅

报告人简介：

Andrius Baltuška received the diploma in physics from Vilnius University, Lithuania, in 1993 and a Ph.D. degree in chemical physics from the University of Groningen, The Netherlands, in 2000. Since 2006 he is a full professor at the faculty of Electrical Engineering and Information Technology, Vienna University of Technology. His group (http://atto.photonik.tuwien.ac.at)works on the development of intense ultrafast laser and parametric amplifiers and applications of fully controlled optical pulses in ultrafast spectroscopy and high-field physics. He received a European Young Investigator Award (EURYI) from the European Science Foundation (2004), Ignaz L. Lieben Award from the Austrian Academy of Sciences (2006) and a Starting Grant (Consolidator) of the European Research Council (2011). In 2016 he was elected a corresponding member of the Austrian Academy of Sciences (ÖAW).

报告内容简介：

Wavelength dependence plays a very significant role in perturbative and non-perturbative nonlinear optics. Using various high-intensity laser and parametric sources developed in our group at the Photonics Institute of TU Wien, we have been systematically studying the limits of enhancing peak power at the fundamental optical frequency through external pulse compression and working on optimizing the conversion efficiency from the fundamental frequency into the extremely low, THz, and extremely high, X-ray, spectral ranges. The talk will focus on the most recent developments obtained with 4-µm mid-IR pulses in the anomalous dispersion regime and with 1-µm near-IR pulses in the normal dispersion regime. One of the main challenges of this work is to find the tradeoffs between the favorable wavelength quadratic scaling laws in plasma-based secondary sources and the overall loss of efficiency due to parametric frequency conversion.

We show that the long wavelength of the mid-IR driver pulse from an optical parametric amplifier enables extremely efficient THz pulse generation in the two-color laser-driven air plasma configuration, permitting record-breaking laser-to THz frequency conversion efficiency above 1%. We also demonstrate that the interplay of the input pulse chirp, air dispersion and molecular absorption make it possible to generate spatially and temporally stable 4-µm laser bullets that are sustained over 10 m propagation distances.

For the 1-µm driver source based directly on the output of an Yb laser amplifier, we show the possibility of obtaining TW peak power and a few-cycle pulse duration using two different pulse compression techniques. Such a near-IR driver source is proved to be optimal for generating high-flux coherent soft X-ray pulses around 7-nm wavelength via high-order harmonic generation. As a proof-of-concept experiment, we demonstrate time- and space-resolved on the picosecond re-magnetization dynamics in a rare-earth Tb metal sample induced by optical pulses and probed by the spectrally filtered X-ray continuum.