Zhengzheng Liu

200 J high efficiency Ti:sapphire chirped pulse amplifier pumped by temporal dual-pulse

We report on an experimental and theoretical study of a large-aperture Ti:Sapphire (Ti:S) amplifier pumped with a novel temporal dual-pulse scheme to suppress the parasitic lasing (PL) and transverse amplified spontaneous emission (TASE) for high-energy chirped-pulse amplification (CPA). The pump energy distribution was optimized and the time delay between each pump pulse was controlled precisely. Both the numerical and experimental results confirm that the temporal dual-pulse pump technique can effectively suppress PL and TASE. The maximum output energy of 202.8 J was obtained from the final 150-mm-diameter Ti:S booster amplifier with a pump energy of 320.0 J, corresponding to a conversion efficiency of 49.3%. The compressed pulse duration of 24.0 fs was measured with a throughput efficiency of 64%, leading to a peak power of 5.4 PW. This novel temporal dual-pulse pump technique has potential applications in a 10 PW CPA laser system.

Robust Subwavelength Single-Mode Perovskite Nanocuboid Laser

On-chip photonic information processing systems require great research efforts toward miniaturization of the optical components. However, when approaching the classical diffraction limit, conventional dielectric lasers with all dimensions in nanoscale are difficult to realize due to the ultimate miniaturization limit of the cavity length and the extremely high requirement of optical gain to overcome the cavity loss. Herein, we have succeeded in reducing the laser size to subwavelength scale in three dimensions using an individual CsPbBr3 perovskite nanocuboid. Even though the side length of the nanocuboid laser is only ∼400 nm, single-mode Fabry-Pérot lasing at room temperature with laser thresholds of 40.2 and 374 μJ/cm2 for one- and two-photon excitation has been achieved, respectively, with the corresponding quality factors of 2075 and 1859. In addition, temperature-insensitive properties from 180 to 380 K have been demonstrated. The physical volume of a CsPbBr3 nanocuboid laser is only ∼0.49λ3 (where λ is the lasing wavelength in air). Its three-dimensional subwavelength size, excellent stable lasing performance at room temperature, frequency up-conversion ability, and temperature-insensitive properties may lead to a miniaturized platform for nanolasers and integrated on-chip photonic devices in nanoscale.

Design of intense 1.5-cycle pulses generation at 3.6 µm through a pressure gradient hollow-core fiber.

We theoretically study the nonlinear compression of the 10-mJ, 62-fs, 3.6-µm laser pulses in an argon gas-filled hollow-core fiber with large diameter of 1000 µm. Using a pressure gradient to restrict undesirable nonlinear effect such as ionization, especially at the entrance, we obtain the intense 18.3-fs (~1.5 cycle) pulses at 3.6 µm only through compression with CaF2 crystal, which can be used as an ultrafast source for strong field driven experiments. In addition, we calculate and discuss the relation between optimal fiber length and coupling efficiency for a given bandwidth. These results are useful for the design of using hollow-core fiber to compress the high-energy pulses with long wavelength.

High-contrast front end based on cascaded XPWG and femtosecond OPA for 10-PW-level Ti:sapphire laser

By combining cross-polarized wave generation and femtosecond optical parametric amplification, a high-contrast front end featuring ultrahigh contrast, a broadband spectrum, an excellent beam profile, and good stability is built for a 10-PW-level Ti:sapphire laser in the Shanghai Superintense Ultrafast Laser Facility (SULF-10PW laser). The front end can deliver a cleaned pulse with a 110 μJ energy at 1 kHz, and the bandwidth of the cleaned pulse exceeds 60 nm (FWHM), which can support a 17 fs compressed pulse duration. The measured output energy fluctuation in one hour is <1.8% in rms value. The measurement-limited contrast is 10-10 at 3 ps before the main pulse. Utilizing the high-contrast front end, single-shot contrast at 10-10 level has been demonstrated in the SULF-10PW laser at a 24 fs pulse duration.

Dispersion management of the SULF front end

To manage dispersion of the front end in the Shanghai Superintense Ultrafast Laser Facility (SULF), which is a largescale project aimed at delivering 10 PW laser pulses, a stretcher based on a combination of a grating and a prism (grism) pair is inserted between an Offner-triplet-type stretcher and a regenerative amplifier to reduce high-order dispersion introduced by optical materials at the amplification stage. The alignment of the grism pair is implemented by controlling the far-field pattern of the output beam of the grism pair. The energy of the front end reaches up to 7 J at a 1-Hz repetition rate. Experimental results show that the pulse duration can be compressed to 22.4 fs and the spectral distortion over the spectrum is less than 2.25 rad.

Ultrafast dynamics of multi-exciton state coupled to coherent vibration in zinc chlorin aggregates for artificial photosynthesis

Ultrafast vibronic dynamics induced by the interaction of the Frenkel exciton with the coherent molecular vibrations in a layer-structured zinc chlorin aggregates prepared for artificial photosynthesis have been studied by 7.1 fs real-time vibrational spectroscopy with multi-spectrum detection. The fast decay of 100 ± 5fs is ascribed to the relaxation from the higher multi-exciton state (MES) to the one-exciton state, and the slow one of 863 ± 70fs is assigned to the relaxation from Q-exciton state to the dark nonfluorescent charge-transfer (CT) state, respectively. In addition, the wavelength dependences of the exciton-vibration coupling strength are found to follow the zeroth derivative of the transient absorption spectra of the exciton. It could be explained in term of the transition dipole moment modulated by dynamic intensity borrowing between the B transition and the Q transition through the vibronic interactions.

Dynamics of Non-linear Photo-Excited Multi-Exciton State Coupled to Coherent Vibration in J Aggregate

The excitonic relaxation and coherent vibrational dynamics in stairlike zinc chlorin aggregates prepared for mimicking chlorosome in nature have been studied by 6.8fs real-time laser spectroscopy.

Nonlinear compression of picosecond chirped pulse from thin-disk amplifier system through a gas-filled hollow-core fiber*

We theoretically study the nonlinear compression of a 20-mJ, 1030-nm picosecond chirped pulse from the thin-disk amplifier in a krypton gas-filled hollow-core fiber. The chirp from the thin-disk amplifier system has little influence on the initial pulse, however, it shows an effect on the nonlinear compression in hollow-core fiber. We use a large diameter hollow waveguide to restrict undesirable nonlinear effects such as ionization; on the other hand, we employ suitable gas pressure and fiber length to promise enough spectral broadening; with 600-μm, 6-bar (1 bar = 105Pa), 1.8-m hollow fiber, we obtain 31.5-fs pulse. Moreover, we calculate and discuss the optimal fiber lengths and gas pressures with different initial durations induced by different grating compression angles for reaching a given bandwidth. These results are meaningful for a compression scheme from picoseconds to femtoseconds. ? 2016 Chinese Physical Society and IOP Publishing Ltd.