Generation Of Coherent Beams Research Articles

Partially coherent beam generation with metasurfaces

An optical system for the generation of partially coherent beams with genuine cross-spectral density functions from spatially modulated globally incoherent sources is presented. The spatial intensity modulation of the incoherent source is achieved by quasi-planar metasurfaces based on spatial-frequency modulation of binary Bragg surface-relief diffraction gratings. Two types of beams are demonstrated experimentally: (i) azimuthally periodic, radially quasi-periodic beams and (ii) rotationally symmetric Bessel-correlated beams with annular far-zone radiation patterns.

Supercontinuum Generation in Photonic Crystal Fibers Infiltrated with Liquids

In this paper we present the development of a new direction in so-called optofluidics , namely the research of photonic crystal fibers (PCF) infiltrated with liquids. In particular we concentrate on the flagship application of PCF, the process of Supercontinuum Generation (SG), in which injected monochromatic pulse may be dramatically broadened (spectrally), which creates a coherent beam generation of high brightness comparable to that of monochromatic lasers. The supercontinuum is formed when a collection of nonlinear processes act together upon a pump beam in order to cause severe spectral broadening of the original pump beam. Explanation of this process is based on numerical simulations for Generalized Nonlinear Schrödinger equation (GNLSE) which describes the rich nonlinear dynamics of pulse propagation in nonlinear dispersive media. All nonlinear phenomena involved in SG will be analyzed. We present specially activity of the Polish-Vietnamese Group from the beginning in 2016 to recent time in this domain.

Graphic processing unit accelerated real-time partially coherent beam generator

A method of using liquid-crystals (LCs) to generate a partially coherent beam in real-time is described. An expression for generating a partially coherent beam is given and calculated using a graphic processing unit (GPU), i.e., the GeForce GTX 680. A liquid-crystal on silicon (LCOS) with 256×256 pixels is used as the partially coherent beam generator (PCBG). An optimizing method with partition convolution is used to improve the generating speed of our LC PCBG. The total time needed to generate a random phase map with a coherence width range from 0.015mm to 1.5mm is less than 2.4ms for calculation and readout with the GPU; adding the time needed for the CPU to read and send to LCOS with the response time of the LC PCBG, the real-time partially coherent beam (PCB) generation frequency of our LC PCBG is up to 312Hz. To our knowledge, it is the first real-time partially coherent beam generator. A series of experiments based on double pinhole interference are performed. The result shows that to generate a laser beam with a coherence width of 0.9mm and 1.5mm, with a mean error of approximately 1%, the RMS values needed 0.021306 and 0.020883 and the PV values required 0.073576 and 0.072998, respectively.

The effect of temperature on a double-barrier generator of terahertz coherent phonons

Abstract In this work we study the generation of coherent beams of terahertz acoustic phonons in GaAs-Al x Ga1− x As double barrier heretostruture (DBH). In this device, for a given external potential, the electrons in the excited level relax in the well emitting GaAs LO phonons. Due to anharmonicity, the LO phonon decays into a pair of phonons LO and TA. The TA phonons form an intense coherent beam in the [111] direction. The Keldysh non-equilibrium formalism is used to calculate the electronic current through the double barrier at finite temperatures. The system is described by a tight-binding Hamiltonian that includes the electrons, the phonons and the electron-phonon interaction. In our results, we analyze the behavior of the TA phonon emission rates (saser) when the temperature is increased.

Study of acousto-optic Q-switched green laser with high efficiency，high stability and high-quality coherent beam generation

High-power and high efficient coherent beam generation with good green-beam quality has been achieved by optimizing the diode-side-pumped linear cavity geometry with two modules in tandem, acousto-optic Q-switching and with S-KTP of Ⅱ-type phase-matching for intracavity frequency doubling of a Nd：YAG laser. When the pump current is 45A, the maximum average green output power of 132 W is obtained with pulse width of 120 ns at pulse repetition rate of 15 kHz, corresponding to the conversion efficiency of 132% from diode pump power to green output power. The M2 beam quality factor is 67 at output power of 130 W, and the output power instability is less than 05% at the same output power during an hour measurement time. The thermo-lensing effect of the laser medium and the stable region of the laser cavity under high power pumping are also theoretically analyzed and experimentally researched.

Observation of multiple-harmonic radiation induced from a gold surface by picosecond neodymium-doped yttrium aluminum garnet laser pulses.

Illuminating a gold surface by strong (5 GW/${\mathrm{cm}}^{2}$) picosecond neodymium-doped yttrium aluminum garnet laser pulses at grazing incidence, we observed a generation of coherent beams of both even and odd harmonics up to fifth order in the reflected direction with efficiencies ${10}^{\mathrm{\ensuremath{-}}10--}$${10}^{\mathrm{\ensuremath{-}}13}$. The observed decrease of the harmonic efficiencies with increasing harmonic order is much weaker than predicted by perturbative theories.

Prospects for high-power KrF lasers

This paper reviews the current status of high-power KrF lasers and considers their prospects for future development. The main laser requirements imposed by target physics considerations are identified and KrF lasers are shown to be uniquely capable of satisfying them. Some design considerations are given for (a) ultrashort-pulse high-power systems, (b) high-power coherent beam generation using Raman amplifiers, and (c) incoherent beam amplification.

High-frequency instability of the sheath–plasma resonance

Coherent high-frequency oscillations near the electron plasma frequency (ω≲ωp) are generated by electrodes with positive dc bias immersed in a uniform Maxwellian afterglow plasma. The instability occurs at the sheath–plasma resonance and is driven by a negative rf sheath resistance associated with the electron inertia in the diodelike electron-rich sheath. With increasing dc bias, i.e., electron transit time, the instability exhibits a hard threshold, downward frequency pulling, line broadening, and copious harmonics. The fundamental instability is a bounded oscillation caused by wave evanescence, but the harmonics are radiated as electromagnetic waves from the electrodes acting like antennas. Wavelength and polarization measurements confirm the emission process. Electromagnetic waves are excited by electrodes of various geometries (planes, cylinders, spheres), which excludes other radiation mechanisms such as orbitrons or beam–plasma instabilities. The line broadening mechanism has been identified as a frequency modulation via the electron transit time by dynamic ions. Ion oscillations at the sheath edge give rise to burstlike rf emissions. These laboratory observations of a new instability are important for antennas in space plasmas, generation of coherent beams with diodes, and plasma diagnostics.