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