Ultraintense few-cycle infrared laser generation by fast-extending plasma grating

Ultraintense short-period infrared laser pulses play an important role in frontier scientific research,but their power is quite low when generated using current technology.This paper demonstrates a scheme for generating an ultraintense few-cycle infrared pulse by directly compressing a long infrared pulse.In this scheme,an infrared picosecond-to-nanosecond laser pulse counterpropagates with a rapidly extending plasma grating that is created by ionizing an undulated gas by a short laser pulse,and the infrared laser pulse is reflected by the rapidly extending plasma grating.Because of the high expansion velocity of the latter,the infrared laser pulse is compressed in the reflection process.One-and two-dimensional particle-in-cell simulations show that by this method,a pulse with a duration of tens of picoseconds in the mid-to far-infrared range can be compressed to a few cycles with an efficiency exceeding 60%,thereby making ultraintense few-cycle infrared pulses possible.

Laser compression via fast-extending plasma gratings

A method is proposed for compressing laser pulses by fast-extending plasma gratings(FEPGs),which are created by ionizing a hypersonic wave generated by stimulated Brillouin scattering in a background gas.Ionized by a short laser pulse,the phonon forms a light-velocity FEPG to fully reflect a resonant pump laser.As the reflecting surface moves with the velocity of light,the reflected pulse is temporally overlapped and compressed.One-and two-dimensional fully kinetic particle-in-cell simulations with a laser wavelength of 1μm show that in this regime,a pump pulse is compressed from 10–40 ps to 7–10 fs(i.e.,a few optical cycles),with a two-dimensional transfer efficiency up to 60%.This method is a promising way to produce critical laser powers while avoiding several significant problems that arise in plasma-based compressors,including an unwanted linear stage,major plasma instabilities,and the need for seed preparation.

Helium Isotopic Composition of the Songduo Eclogites in the Lhasa Terrane,Tibet: Information from the Deep Mantle

Helium isotopic compositions are considered to be ideal tracers to identify whether mantle materials have been added to crustal rocks or fluids.In this paper,we present the helium isotopic compositions of the Songduo eclogites in the Lhasa terrane,Tibet.We found that garnet and omphacite in the eclogites have different helium retention characteristics.The 4He content of most omphacite grains are about 10–20 times of that of garnet,suggesting that omphacite has a higher ability to capture 4He than garnet.Similarly,there is about 10–20 times difference in 3He content between omphacite and garnet in the same eclogite samples.The 3He/4He ratios of garnet and omphacite in these rocks range from 0.27 to 0.60 Ra(relative to the modern air 3He/4He ratio,1.4×10^-6).These ratios are within the range of both mantle-and crust-derived helium,suggesting mixed sources.The Songduo eclogites have much higher3He/4He ratios than those observed in the Dabie eclogites of eastern China.Such high ratios are typically thought to be associated with deep mantle sources.We cautiously conclude that deep mantle materials might have been involved during the formation of the Songduo eclogites.