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Creators/Authors contains: "Chang, Zenghu"

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  1. ; ; ; (, Optics Letters)
    Few-cycle pulses were generated by passing a beam from a cryogenically cooled Fe:ZnSe chirped-pulse amplifier (CPA) at a repetition rate of 400 Hz through a gas-filled hollow core fiber (HCF) followed by dispersion-compensating bulk CaF2. The krypton-filled fiber at 370 kPa yielded 1.14-mJ, 42-fs pulses centered at 4.07 µm, while the oxygen-filled fiber at 310 kPa delivered 0.78-mJ, 39-fs pulses spanning from 3 to 5.5 µm. This work is a step toward a high repetition rate mid-wave infrared driver of isolated attosecond keV x-ray pulses. 
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  2. ; ; ; (, Optics Express)
    We theoretically and computationally study the generation of high-order harmonics in the water window from a semi-infinite gas cell where a few-cycle, carrier-envelope-phase-controlled 1.7-µm driving laser pulse undergoes nonlinear propagation via optical Kerr effect (self-focusing) and plasma defocusing. Our calculation shows that high harmonic signals are enhanced for extended propagation distances and furthermore, isolated attosecond pulses in the water window can be generated from the semi-infinite gas cell. This enhancement is attributed mainly to better phase matching for extended propagation distances achieved via nonlinear propagation and resulting intensity stabilization. 
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  3. ; ; ; (, Optics Express)
    A femtosecond chirped pulse amplifier based on cryogenically cooled Fe:ZnSe was demonstrated at 333 Hz—33 times higher than previous results achieved at near-room-temperature. The long upper-state lifetime allows free-running, diode-pumped Er:YAG lasers to be used as pump lasers. 250-fs, 4.59-mJ pulses are produced with a center wavelength of 4.07 µm, which avoids strong atmospheric CO2absorption that cuts on around 4.2 µm. It is therefore possible to operate the laser in ambient air with good beam quality. By focusing the 18-GW beam in air, harmonics up to the ninth order were observed indicating its potential for use in strong-field experimentation. 
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  4. ; ; (, Sensors)
    Electron correlation describes the interaction between electrons in a multi-electron system. It plays an important role in determining the speed of relaxation of atoms and molecules excited by XUV/X-ray pulses, such as the argon decay rate. Most research on electron correlation has centered on the role of correlation in stationary states. A time-resolved experimental study of electron correlation is a grand challenge due to the required temporal resolution and photon energy. In this research, we investigated Auger decay in argon using 200-attosecond X-ray pulses reaching the carbon K-edge. At such a high photon energy, ionization occurs not only from the outer most levels (3s and 3p), but also from the 2p core shells. We have measured a lifetime of 4.9 fs of L-shell vacancies of argon in pump–probe experiments with a home-built high-resolution time-of-flight spectrometer. 
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  5. ; ; ; (, Optics Letters)
    3.2-mJ, 92-fs pulses centered at 3.1 µm are generated at a 1-kHz repetition rate through a tabletop optical parametric chirped pulse amplification (OPCPA) system based on ZnGeP2crystals. Pumped by a 2-µm chirped pulse amplifier with a flat-top beam profile, the amplifier achieves a 16.5% overall efficiency, which, to the best of our knowledge, is the highest efficiency achieved by OPCPA at this wavelength. Harmonics up to the seventh order are observed after focusing the output in the air. 
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  6. ; ; ; (, Optics Continuum)
    It is well known that the gain and efficiency of an amplifier with a quasi-three level medium such as Ho:YLF is strongly affected by the coolant temperature. By cooling the Ho:YLF crystals of a two-stage energy booster in a Ho:YLF Chirped Pulse Amplification laser with -20°C thermoelectric cooling rather than room temperature water, a 60 mJ pulse energy at 1 kHz repetition rate was achieved with 8.5 mJ input. 
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  7. ; ; ; ; ; ; ; ; ; ; et al (, The International Conference on Ultrafast Phenomena (UP) 2022)
    Half-cycle oscillation is observed in transient absorption spectra of N2O at NKedge (400 eV) irradiated by intense IR pulses, which is attributed to tunneling ionization of core excited states by intensive TDSE-based simulation. 
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  8. ; ; ; ; ; ; ; ; ; ; et al (, Physical Review Research)
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  9. ; ; ; ; ; (, Scientific Reports)
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  10. (, OSA Continuum)