We report results of numerical simulations on the multiple soliton generation and soliton energy quantization in a soliton fiber ring laser passively mode-locked by using the nonlinear polarization rotation technique. We found numerically that the formation of multiple solitons in the laser is caused by a peak power limiting effect of the laser cavity.It is also the same effect that suppresses the soliton pulse collapse, an intrinsic feature of solitons propagating in the gain media, and makes the solitons stable in the laser.Furthermore, we show that the soliton energy quantization observed in the lasers is a natural consequence of the gain competition between the multiple solitons. Enlightened by the numerical result we speculate that the multi-soliton formation and soliton energy quantization observed in other types of soliton fiber lasers could have similar mechanism.

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Recent advances in attosecond science have relied upon the nearly instantaneous response of free electrons to an external field. However, it is still not clear whether bound electrons are able to rearrange on sublaser cycle time scales. Here, we probe the optical Stark shifts induced by a few-cycle near infrared laser field in helium bound states using isolated attosecond pulses in a transient absorption scheme and uncover a subcycle laser-induced energy level shift of the laser-dressed 1s3p state.

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High-order-harmonic-generation yield is remarkably sensitive to driving laser ellipticity, which is interesting from a fundamental point of view as well as for applications. The most well-known example is the generation of isolated attosecond pulses via polarization gating. We develop an intuitive semiclassical model that makes use of the recently measured initial transverse momentum of tunneling ionization. The model is able to predict the dependence of the high-order-harmonic yield on driving laser ellipticity and is in good agreement with experimental results and predictions from a numerically solved time-dependent Schrödinger equation.

Gamma-ray photons with energy >9  MeV were produced when second-harmonic-generated laser light (3 eV) inverse-Compton-scattered from a counterpropagating relativistic (~450  MeV) laser-wakefield-accelerated electron beam. Two laser pulses from the same laser system were used: one to accelerate electrons and one to scatter. Since the two pulses play very different roles in the γ-ray generation process, and thus have different requirements, a novel laser system was developed. It separately and independently optimized the optical properties of the two pulses. This approach also mitigated the deleterious effects on beam focusing that generally accompany nonlinear optics at high peak-power levels.

New parasitic lasing suppression techniques are developed and high gain amplification is demonstrated in a petawatt level Ti:sapphire amplifier based on the chirped pulse amplification (CPA) scheme. Cladding the large aperture Ti:sapphire with refractive-index matched liquid doped with absorber suppresses the transverse lasing. The acousto-optic programmable dispersive filter (AOPDF) is used to realize side-lobe suppression in the temporal profile of the compressed pulse. The 800 nm laser output with peak power of 0.89 PW and pulse width of 29.0 fs is demonstrated.

[1] Until recently, global high spatial resolution maps of FeO and TiO 2 of the Moon were only derived from Clementine data. In this study, we show global maps of FeO and TiO 2 using Chang'E-1 Interference Imaging Spectrometer (IIM) at a spatial resolution of 200 m/pixel. With a newly developed calibration presented here, spectra obtained by IIM compare well with telescopic spectra. Spectral parameters previously shown to be sensitive to iron and titanium, derived from the calibrated IIM data are highly correlated with the measured elemental concentration with R 2 = 0.96 for FeO and 0.95 for TiO 2 . The maps were developed using this calibration. Histograms of basalt FeO estimates have a negatively skewed distribution, while TiO 2 distributions are unimodal. They also revealed that the lunar highland crust is relatively uniform on the quadrant scale (several hundred to thousand kilometers scale) but inhomogenous on the global scale. The area of highest elevation of the Moon has very low FeO and TiO 2 raising the question about South Pole-Aitken (SPA) (whether its ejecta deposits covered the highest elevation and when it was formed). Although the average FeO and TiO 2 abundances for basalts are highly correlated, local areas of elevated iron can be associated with both high and low titanium.