Teng Hao

Generation of Sub-2 Cycle Optical Pulses with a Differentially Pumped Hollow Fiber

We report the generation of optical pulses with an energy of 0.55 m J and duration of 1.6-cycle (4.4 fs) at repetition rate of 1 kHz using a differentially pumped hollow fiber and chirped mirrors. Compared to the statically gasfilled scheme, the differentially pumping hollow fiber is demonstrated to support more energy output with higher transmission efficiency, and to increase the spectral broadening due to a reduction of ionization defocusing in plasma at the fiber entrance. The differentially pumping technique is proved to be an effective way to obtain optical pulses with mono-cycle and higher energy.

Generation and Measurement of Isolated 160-Attosecond XUV Laser Pulses at 82 eV

Isolated attosecond extreme-ultraviolate (XUV) pulses are generated based on high-harmonic-generation from a neon gas cell driven by carrier-envelope phase stabilized sub-5-fs Ti:sapphire laser pulses at repetition rate of 1 kHz. Temporal characterization of isolated attosecond XUV pulses is demonstrated to be 160-attosecond by attosecond streaking spectroscopy. The development of attosecond source and streaking spectroscopy will allow scientists to explore the electron dynamics in matter.

Generation of 170-fs Laser Pulses at 1053 nm by a Passively Mode-Locked Yb:YAG Laser

A novel method is developed to obtain 1.05 μm laser operation with a Yb:YAG laser. By using a Yb:YAG crystal with proper length and doping concentration, a femtosecond Yb:YAG laser is realized at the central wavelength of 1053 nm. The measured pulse duration and spectral bandwidth (FWHM) are 170 fs and 7 nm; the repetition rate is 80 MHz. Under a power pump of 2 W, an average mode-locking power of 180 mW is achieved.

Generation of Continuum Extreme-Ultraviolet Radiation by Carrier-Envelope-Phase-Stabilized 5-fs Laser Pulses

Coherent extreme-ultraviolet (XUV) radiation is studied by interaction of carrier-envelope (CE) phase stabilized high energy 5-fs infrared (800 nm) laser pulses with neon gas at a repetition rate of 1 kHz. A broadband continuum XUV spectrum in the cut-off region is demonstrated when the CE phase is shifted to about zero, rather than modulated spectral harmonics when setting of CE phase is nonzero. The results show the generation of isolated attosecond XUV pulses.

Synchronously Pumped Femtosecond Optical Parametric Oscillator Based on MgO-Doped Periodically Poled LiNbO3

We report a femtosecond optical parametric oscillator based on MgO-doped PPLN synchronously pumped by a mode-locked Ti:sapphire laser. The wavelengths of the signal and idler are continuously tuned from 1100 to 1300 nm and from 2080 to 2930 nm, respectively, by changing the pump wavelength and the OPO cavity length. The maximum signal output power of 130 mW at the wavelength of 1225 nm is obtained, pumped by 900 mW of 800 nm laser radiation. This corresponds to a total conversion efficiency of 22.1%. The signal pulse duration is measured to be 167 fs by intensity autocorrelation with chirped mirrors for intracavity dispersion compensation.

Generation of Femtosecond Laser Pulse at 1053 nm with Contrast of 10−11 by Optical-Parametric Amplification

We demonstrated a high contrast 1053 nm femtosecond laser by exchanging the signal and idler in two stages non-collinear optical-parametric amplifier, 60 μI idler with measurement-limited contrast of 2.3×1011 was obtained within scale of sub-10 ps.

A 100-TW Ti:Sapphire Laser System at a Repetition Rate of 0.1 Hz

We demonstrate a 100-TW-class femtosecond Tr:sapphire laser running at a repetition rate of 0.1 Hz based on a 20 TW/10 Hz laser facility (XL-II). Pumping the new stage amplifier with a 25J green Nd:glass laser, we successfully improve the laser energy to 3.4 J with duration of 29 fs, corresponding to a peak power of 117 TW.

Prospects for femtosecond ultrahigh intensity laser system towards Exawatt level

The new generation system for ultrahigh-power laser running over Exawatt (EW, 10 18  W) level is emerging recently, which is under a mechanism called Raman backscattering (RBS) in plasma. The main advantage of using plasma is that it can tolerate much higher laser intensities, 10 17  W cm −2 , more than five order of solid-state devices limited, 10 12  W cm −2 . Although Petawatt (PW, 10 15  W) laser pulses have been realized by some groups based on the chirped pulse amplification scheme (CPA), many cutting-edge scientific researches and technical applications, such as inertial confinement fusion (ICF), plasma physics, astrophysics, plasma-based particle accelerators, and X-ray lasers, need even higher laser power than EW level. For these purposes, huge laser projects like the extreme light infrastructure (ELI) have been proposed to offer new paradigm in EW class laser power. However, such an ultrahigh intensity laser system could only be achieved by CPA using very large (beyond 1 m 2 ) and expensive compressor gratings. In addition, to extrapolate CPA to the EW power range, hundreds of such gratings would be required. Even if there is enough budget, the problem of energy restriction on the last grating is still under question. Therefore, it is crucial to find a new medium or new technology for generating femtosecond ultra-intense laser pulses. This paper introduces a solution for generating laser intensities many orders of magnitude higher than currently results. This technology of optical amplification that a process known as Raman backscattering amplification and compression could enable the generation of femtosecond pulses of 20000 times the original seed intensity in a column of plasma just a few millimeters in length and less than a millimeter in width, without stretcher and compressor. Such sufficient high intensity and lower frequency of the pulse amplification indeed have got into super-radiant amplification regime (SRA) or stimulated Raman backscattering (SRBS). It has revealed that an unprecedented large pulse intensity amplification could be realized. The seed pulse will be compressed to 25 fs and its unfocused intensity increased from 1×10 15 to 4×10 17  W cm −2 . Furthermore, it could be increased further to around 1×10 23 W cm −2 by focusing the resulting beam to 1 μm. Therefore, it might be possible to increase this power up to EW in a larger plasma and using more powerful optical pumping.

Tunable, High-Order Harmonically Mode-Locked All-Normal-Dispersion Ytterbium Fiber Laser

We report the generation of passively tunable high peak signal-to-noise ratio harmonic mode-locked (HML) all-normal-dispersion Yb-doped fiber laser with a single birefringent filter in a ring cavity configuration. The highest fourth harmonic of the fundamental mode-locked frequency at a repetition rate of 88 MHz is obtained. The pulses are compressed to 627 fs by using an external grating-pair compressor. For the fourth HML output, the peak signal-to-noise ratio of the rf is 73 dB and the average power is as high as 110 mW with the pump power of 500 mW. Soliton bunches which contain multipulses are also observed in the weak mode-locked regime of the HML, and the separation between interpulses in a dissipative soliton bunch can be controlled by adjustment of the waveplates and spectral filter in the cavity.

Fabrication of 16 W all-normal-dispersion mode-locked Yb-doped rod-type fiber laser with large-mode area*

A mode-locked ytterbium-doped rod-type fiber laser with 85 μm core diameter is developed based on the nonlinear polarization evolution in an all-normal-dispersion ring cavity, in which a uniaxial birefringent plate is used as the spectral filter. Average power up to 16 W is obtained at the repetition rate of 58 MHz, and the pulse duration is compressed to 182 fs with a grating-pair compressor. The output laser pulses show very good beam quality and power stability.