Coherent X-ray and extreme ultraviolet pulses with attosecond duration are critical tools for observing and controlling electron motions in matter. The generation and characterization of such pulses is a new frontier in ultrafast optics. Zenghu Chang has developed major innovative means for generation and characterization of ultrabroadband single isolated attosecond pulses for pump-probe experiments. He pioneered high harmonic generation in noble gases with long wavelength lasers for extending the cutoff photon energy. In 2001, his group demonstrated the dramatic cutoff extension of high-order harmonic generation in the extreme ultraviolet by driving the nonlinear process with long wavelength optical parametric amplifier lasers [Phys. Rev. A 65, 011804(R) (2001). They also experimentally investigated the effects of quantum diffusion of electron wavepackets on the conversion efficiency of high harmonic generation process for the first time. In 2017, by driving high harmonic generation with a carrier-envelope phase locked laser at 1.7 micron center wavelength and applying polarization gating, single isolated attosecond X-ray pulses in the 50 to 450 eV range were generated in his lab. The measured duration of the X-ray pulse is 53 as [Nature Photonics 8, 186 (2017)], which is the shortest X-ray at the Carbon K-edge (~280 eV). He is currently interested in developing intense MIR lasers for generating keV attosecond pulses [Optics Letters 43, 3381 (2018)] and applying Machine Learning to attosecond science [Optics Express 27, 4799 (2019)].
Design and fabrication of transmission gratings with high diffraction efficiency for pulse compression
Design of high-efficiency broad-bandwidth pulse compression device based on composite transmission grating with high damage threshold
Control of multiphoton and avalanche ionization using an ultraviolet-infrared pulse train in femtosecond laser micro/nano-machining of fused silica
Measurement of attosecond XUV pulses generated with polarization gating by two-dimensional photoelectron spectroscopy