232 research outputs found
Intense keV isolated attosecond pulse generation by orthogonally polarized multicycle midinfrared two-color laser field
We theoretically investigate the generation of intense keV attosecond pulses
in an orthogonally polarized multicycle midinfrared two-color laser field. It
is demonstrated that multiple continuum-like humps, which have a spectral width
of about twenty orders of harmonics and an intensity of about one order higher
than adjacent normal harmonic peaks, are generated under proper two-color
delays, owing to the reduction of the number of electron-ion recollisions and
suppression of inter-half-cycle interference effect of multiple electron
trajectories when the long wavelength midinfrared driving field is used. Using
the semiclassical trajectory model, we have revealed the two-dimensional
manipulation of the electron-ion recollision process, which agrees well with
the time frequency analysis. By filtering these humps, intense isolated
attosecond pulses are directly generated without any phase compensation. Our
proposal provides a simple technique to generate intense isolated attosecond
pulses with various central photon energies covering the multi-keV spectral
regime by using multicycle driving pulses with high pump energy in experiment.Comment: 11 pages,5 figures, research articl
Pure Even Harmonic Generation from Oriented CO in Linearly Polarized Laser Fields
The first high harmonic spectrum, containing only the odd orders, was
observed in experiments 30 years ago (1987). However, a spectrum containing
pure even harmonics has never been observed. We investigate the generation of
pure even harmonics from oriented CO molecules in linearly polarized laser
fields employing the time-dependent density-functional theory. We find that the
even harmonics, with no odd orders, are generated with the polarization
perpendicular to the laser polarization, when the molecular axis of CO is
perpendicular to the laser polarization. Generation of pure even harmonics
reveals a type of dipole acceleration originating from the permanent dipole
moment. This phenomenon exists in all system with permanent dipole moments,
including bulk crystal and polyatomic molecules
Initial carrier-envelope phase of few-cycle pulses determined by THz emission from air plasma
The evolution of THz waveform generated in air plasma provides a sensitive
probe to the variation of the carrier envelope phase (CEP) of propagating
intense few-cycle pulses. Our experimental observation and calculation reveal
that the number and positions of the inversion of THz waveform are dependent on
the initial CEP, which is near 0.5{\pi} constantly under varied input pulse
energies when two inversions of THz waveform in air plasma become one. This
provides a method of measuring the initial CEP in an accuracy that is only
limited by the stability of the driving few-cycle pulses.Comment: 13 pages, 4 figure
A multistep pulse compressor for 10s to 100s PW lasers
High-energy tens (10s) to hundreds (100s) petawatt (PW) lasers are key tools
for exploring frontier fundamental researches such as strong-field quantum
electrodynamics (QED), and the generation of positron-electron pair from
vacuum. Recently, pulse compressor became the main obstacle on achieving higher
peak power due to the limitation of damage threshold and size of diffraction
gratings. Here, we propose a feasible multistep pulse compressor (MPC) to
increase the maximum bearable input and output pulse energies through modifying
their spatiotemporal properties. Typically, the new MPC including a prism pair
for pre-compression, a four-grating compressor (FGC) for main compression, and
a spatiotemporal focusing based self-compressor for post-compression. The prism
pair can induce spatial dispersion to smooth and enlarge the laser beam, which
increase the maximum input and output pulse energies. As a result, as high as
100 PW laser with single beam or more than 150 PW through combining two beams
can be obtained by using MPC and current available optics. This new optical
design will simplify the compressor, improve the stability, and save expensive
gratings/optics simultaneously. Together with the multi-beam tiled-aperture
combining method, the tiled-grating method, larger gratings, or negative chirp
pulse based self-compression method, several 100s PW laser beam is expected to
be obtained by using this MPC method in the future, which will further extend
the ultra-intense laser physics research fields.Comment: 18 pages, 10 figure
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