New generation attosecond X-rays for ultrafast spectroscopy and imaging

Zenghu Chang

Institute for the Frontier of Attosecond Science and Technology, CREOL and Physics Department, University of Central Florida, Orlando, USA. Abstract


Shortest X-ray pulses, 53 as, around the Carbon K-edge (284 eV) characterized by attosecond streaking.

Few-cycle Ti:Sapphire lasers centered at 800 nm have been working horses for attosecond pulse generation for the last 17 years. The spectral range of isolated attosecond pulses with sufficient photon flux for time-resolved pump-probe experiments has been limited to extreme ultraviolet (10 to 150 eV). It was demonstrated in 2001 that the cutoff photon energy of high harmonic spectrum can be extended by increasing the center wavelength of driving lasers [1].

In recent years, mJ level, two-cycle, carrier-envelope phase stabilized lasers at 1.6 to 2.1 micron have been developed by compressing pulses from Optical Parametric Amplifiers with gas-filled hollow-core fibers or by implementing Optical Parametric Chirped Pulse Amplification (OPCPA) techniques. When a 3 mJ, 12 fs laser at 1.7 micron laser was used to implement polarization gating, soft X-rays in the water window (280-530 eV) were generated in our laboratory. The number of X-ray photons in the 120–400 eV range per laser shot is comparable to that generated with Ti:Sapphire lasers in the 50 to 150 eV range [2]. Isolated X-ray pulses with 53 as duration were characterized by attosecond streaking measurements [3]. Such ultrabroadband light sources are now being used in time-resolved X-ray absorption near edge structure measurements for studying charge dynamics in atoms and molecules.

This work has been supported Army Research Office (W911NF-14-1-0383, W911NF-15-1-0336); Air Force Office of Scientific Research (FA9550-15-1-0037, FA9550-16-1-0013, FA9550-17-1- 0499); the DARPA PULSE program by a grant from AMRDEC (W31P4Q1310017). This material is also based upon work supported by the National Science Foundation under Grant Number (NSF Grant Number 1806575).

1. Bing Shan, Zenghu Chang, Phys. Rev. A 65, 011804(R) (2001).
2. Jie Li, et al., Applied Physics Letters 108, 231102 (2016).
3. Jie Li et al., Nature Communications 8, 186 (2017).