111 research outputs found
Highly-efficient third-harmonic generation from ultrapure diamond crystals
We report on a direct generation of efficient and wavelength-tunable
third-harmonic generation (THG) from ultrapure electronic-grade (EG) diamond
crystals. Under an ultrafast infrared excitation at 1280 nm, the considerably
high optical conversion efficiency of ~ 0.7% at a THG wavelength of 427 nm is
obtained, and the THG signal can be tuned over ultra-broadband range from 420
to 730 nm. We argue that the THG efficiency is originating from minimum
absorption loss and phase-matching conditions in EG diamond. Enhanced THG from
EG diamond crystal represents a new paradigm for establishing efficient
diamond-based frequency converters, quantum sensing, and quantum communications
platforms.Comment: 8 pages, 4 figure
Forcibly driven coherent soft phonons in GeTe with intense THz-rate pump fields
We propose an experimental technique to generate large amplitude coherent
phonons with irradiation of THz-rate pump pulses and to study the dynamics of
phase transition in GeTe ferroelectrics. When a single pump pulse irradiates
the sample at various pump power densities, the frequency of the soft phonon
decreases sub-linearly and saturates at higher pump powers. By contrast, when
THz-rate pump pulse sequence irradiates the sample at matched time intervals to
forcibly drive the oscillation, a large red-shift of the phonon frequency is
observed without saturation effects. After excitation with a four pump pulse
sequence, the coherent soft phonon becomes strongly damped leading to a near
critical damping condition. This condition indicates that the lattice is driven
to a precursor state of the phase transition.Comment: 4 pages, 3 figure
Ultrafast optical manipulation of atomic arrangements in chalcogenide alloy memory materials
A class of chalcogenide alloy materials that shows significant changes in
optical properties upon an amorphous-to-crystalline phase transition has lead
to development of large data capacities in modern optical data storage. Among
chalcogenide phase-change materials, Ge2Sb2Te5 (GST) is most widely used
because of its reliability. We use a pair of femtosecond light pulses to
demonstrate the ultrafast optical manipulation of atomic arrangements from
tetrahedral (amorphous) to octahedral (crystalline) Ge-coordination in GST
superlattices. Depending on the parameters of the second pump-pulse, ultrafast
nonthermal phase-change occurred within only few-cycles (~ 1 ps) of the
coherent motion corresponding to a GeTe4 local vibration. Using the ultrafast
switch in chalcogenide alloy memory could lead to a major paradigm shift in
memory devices beyond the current generation of silicon-based flash-memory.Comment: 11 pages, 7 figures, accepted for publication in Optics Expres
Control of carrier transport in GaAs by longitudinal-optical phonon-carrier scattering using a pair of laser pump pulses
We demonstrate optical control of the LO phonon-plasmon coupled (LOPC) modes
in GaAs by using a femtosecond pump-pulse pair. The relaxation time of the
plasmon-like LOPC mode significantly depends on the separation time (\Delta t)
of the pump-pulse pair. Especially it is maximized when \Delta t becomes
simultaneously comparable to the half period of the longitudinal optical (LO)
phonon oscillation and resonant to the 3/4 period of the plasmon-like LOPC
oscillation. We attribute these observations to the modification of carrier-LO
phonon scattering and ballistic motion of the plasmon-like LOPC mode.Comment: 5 pages, 4 figures, submitted to Journal of Applied Physic
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