Gain of harmonic generation in high gain free electron laser

In a planar undulator employed free electron laser (FEL), each harmonic radiation starts from linear amplification and ends with nonlinear harmonic interactions of the lower nonlinear harmonics and the fundamental radiation. In this paper, we investigate the harmonic generation based on the dispersion relation driven from the coupled Maxwell-Vlasov equations, taking into account the effects due to energy spread, emittance, betatron oscillation of electron beam as well as diffraction guiding of the radiation field. A 3D universal scaling function for gain of the linear harmonic generation and a 1D universal scaling function for gain of the nonlinear harmonic generation are presented, which promise rapid computation in FEL design and optimization. The analytical approaches have been validated by 3D simulation results in large range.     

Gain of harmonic generation in high gain free electron laser

In a planar undulator employed free electron laser(FEL),each harmonic radiation starts from linear amplification and ends with nonlinear harmonic interactions of the lower nonlinear harmonics and the fundamental radiation.In this paper,we investigate the harmonic generation based on the dispersion relation driven from the coupled Maxwell-Vlasov equations,taking into account the effects due to energy spread,emittance,betatron oscillation of electron beam as well as diffraction guiding of the radiation field.A 3D universal scaling function for gain of the linear harmonic generation and a 1D universal scaling function for gain of the nonlinear harmonic generation are presented,which promise rapid computation in FEL design and optimization.The analytical approaches have been validated by 3D simulation results in large range.     

Optical pulse generation from FM laser using gain dispersion

The possibility of new type of optical pulse compression utilizing dispersion effect of laser gain is discussed. An experiment using a 1.06 μm Nd:YAG laser for a dispersive delay line was performed to demonstrate the possibility, where cw FM laser, instead of frequency-swept pulses, was e,ployed. The FM laser of 100 GHz bandwidth at 144 MHz repetition frequency, which was generated from another Nd:YAG laser, was observed to pulsate with 1.2 ns pulsewidth after passing through the dispersive delay line consisting of laser medium. Several times power amplification due to the laser gain was also obtained in the dispersive delay line.     

Harmonic operation of high gain harmonic generation free electron laser

In high gain harmonic generation (HGHG) free electron laser (FEL), with the right choice of parameters of the modulator undulator, the dispersive section and the seed laser, one may make the spatial bunching of the electron beam density distribution correspond to one of the harmonic frequencies of the radiator radiation, instead of the fundamental frequency of the radiator radiation in conventional HGHG, thus the radiator undulator is in harmonic operation (HO) mode. In this paper, we investigate HO of HGHG FEL.Theoretical analyses with universal method are derived and numerical simulations in ultraviolet and deep ultraviolet spectral regions are given. It shows that the power of the 3rd harmonic radiation in the HO of HGHG may be as high as 18.5% of the fundamental power level. Thus HO of HGHG FEL may obtain short wavelength by using lower beam energy.     

Harmonic operation of high gain harmonic generation free electron laser

In high gain harmonic generation (HGHG) free electron laser (FEL), with the right choice of parameters of the modulator undulator, the dispersive section and the seed laser, one may make the spatial bunching of the electron beam density distribution correspond to one of the harmonic frequencies of the radiator radiation, instead of the fundamental frequency of the radiator radiation in conventional HGHG, thus the radiator undulator is in harmonic operation (HO) mode. In this paper, we investigate HO of HGHG FEL. Theoretical analyses with universal method are derived and numerical simulations in ultraviolet and deep ultraviolet spectral regions are given. It shows that the power of the 3rd harmonic radiation in the HO of HGHG may be as high as 18.5% of the fundamental power level. Thus HO of HGHG FEL may obtain short wavelength by using lower beam energy.     

Absorption and scattering in bismuth-doped optical fibers

The optical-loss spectra of bismuth-doped aluminosilicate glass core optical fibers have been investigated in the spectral range 200–1700 nm. Absorption (active and inactive) and scattering losses have been separated. The optical fibers under study were fabricated by methods of modified chemical vapor deposition and surface-plasma chemical vapor deposition.     

Optical amplification in a bismuth-doped silica glass at 1300 nm telecommunications window

We have demonstrated optical amplification in a bismuth-doped silica glass in second telecommunication windows (1300 nm). The amplification was obtained at five different wavelengths between 1260 and 1360 nm and the amplification bandwidth is greater than 75 nm. This new gain medium is expected to be useful for application in ultra-wide broadband optical communication.     

Broadly tunable second-harmonic generation in periodically poled silica fibers

Broadband tunability of the second-harmonic wavelength is achieved in periodically poled silica fibers. A wavelength tuning range of almost 45 nm of the fundamental wave is demonstrated through mechanical compression tuning of the quasi-phase-matched periodic structure. The uniform strain applied along the entire periodic structure enables the spectral profile and the conversion efficiency of the generated second harmonic to be preserved for the full tuning range. To our knowledge, the achieved tuning range realized through this technique is far greater than that possible with uniform periodically poled crystals.     

Optical losses and gain in silicon-rich silica waveguides containing Er ions

Rib-loaded waveguides containing Er³⁺ coupled to Si-nc have been produced by magnetron sputtering and successive thermal annealing to investigate optical gain at 1535 nm. It has been shown that all Er ions are optically active, whereas the fraction that can be excited at high pump rates under non-resonant excitation is strongly limited by confined carrier absorption (CA), up-conversion processes, and mainly by the lack of coupling to the Si-nc. Er³⁺ absorption cross-section is found comparable to that of Er³⁺ in SiO₂, but a dependence with the effective refractive index has been found. Although the presence of Si-nc strongly improves the efficiency of Er³⁺ excitation, it introduces additional optical loss mechanisms, such as CA. These Si-nc losses affect the possibility of obtaining net optical gain. In the present study, they have been minimized by lowering the annealing time of the Er-doped Si-rich oxide. In pump-probe measurements it is shown that signal enhancement of the transmitted signal can be achieved at low pumping rate when the detrimental role of confined CA is attenuated by reducing the annealing time. A maximum signal enhancement of about 1.30 at 1535 nm was observed.     

Optical properties of high-delta air silica microstructure optical fibers

We analyze the waveguide properties of microstructure optical fibers consisting of a silica core surrounded by a single ring of large air holes. Although the fibers can support numerous transverse spatial modes, coupling between these modes even in the presence of large perturbations is prevented for small core dimensions, owing to a large wave-vector mismatch between the lowest-order modes. The result is an optical fiber that can appear single mode with propagation properties that can be achieved only in multimode waveguides.     

Optical characterization of tunable solid-state laser gain media

The transition metal ions are optical centres that promise tunable laser operation at room temperature over much of the visible and near-infrared regions. This review presents the essential characteristics used in optical assessment of possible laser-active solids and some of the theory required to understand the experimental results. Also presented is a survey of the main features of the optical absorption-emission cycle, luminescence decay profiles, optical bandshapes and excited-state absorption for Ti³⁺, Cr³⁺ and Co²⁺ ions in (essentially) octahedral environments. Finally, materials characteristics (for example, radiative against non-radiative decay, excited-state absorption and disorder) that limit laser performance are discussed.     

Electron trajectories and gain in free electron laser with ionchannel guiding

A detailed analysis of electron trajectories and gain in a helical wiggler free electron laser (FEL) with ion channel focusing using single particle dynamics is presented. Conditions for stability of electron orbit have been obtained and stable regimes have been identified. Gain has been evaluated in the low-gain-per-pass limit with the help of the self-consistent pendulum equation. It is seen that the presence of ion channel leads to significant gain enhancement under appropriate conditions     

Optical and ultrasonic monitoring of femtosecond laser filamentation in fused silica

Millimeter-long filaments and accompanying luminous plasma and defect channels created in fused silica (FS) by single focused femtosecond laser pulses with supercritical powers were probed in situ using optical imaging and contact ultrasonic techniques. Above the threshold pulse energy E_opt = 5 μJ corresponding to a few megawatt power levels pulses collapse due to self-focusing, producing channels filled by electron-hole plasma and luminescent defects, and exhibits predominantly compressive pressure transients. Analysis of the optical and ultrasonic response versus the laser pulse energy suggests that filamentary pulse propagation in the channels occurs with considerable dissipation of about ∼10 cm⁻¹. The predominant ionization mechanism is most likely associated with avalanche ionization, while the main mechanism of optical absorption is free-carrier absorption via inverse Bremsstrahlung interaction with the polar lattice.     

High gain weak pump free electron laser amplifier analysis

The one dimensional free electron laser equations are solved in the steady state case for high gain weak pump solutions. The quadratic dispersion relation obtained by series expansion is compatible with the classical cubic form by linearization. The functional dependence of the exponentiation length of the radiation field on the machine parameters can be used as a design guideline.     

Numerical simulation of the generation of gain switched laser pulses

Gain switched laser pulses with FWHM of 32 ps having an optical peak power exceeding 400 W are generated using low cost single heterostructure (SH) Fabry–Perot laser diodes. To examine and to optimize this effect in detail, a thorough physical device simulation is done. Maxwell's equations together with a simplified version of the Boltzmann transport equation (BTE) and various parameters like carrier recombination and material gain, form a coupled set of nonlinear, inhomogeneous partial differential equations, that are discretized using the finite difference scheme and solved selfconsistently.     

A study of the gain mechanism in free electron laser systems

A detailed study of the gain mechanism in low-gain free electron laser systems is presented. The analysis is based on a recently reported analytic solution to the quasi-Bloch equations, which are assumed to govern the evolution of the system.     

Efficient mid-IR spectral generation via spontaneous fifth-order cascaded-Raman amplification in silica fibers

Spontaneous cascaded Raman amplification is demonstrated as a practical and efficient means of power transfer from telecommunications wavelengths to mid-IR wavelength bands through use of conventional silica fibers and amplifiers. We show that silica fibers possessing normal dispersion over all near-IR and mid-IR wavelengths can facilitate 37% and 16% efficient Raman power conversion from 1.53 microm to 2.15 and 2.41 microm wavelength bands, respectively, using nanosecond pulses from an all-fiber laser source. In contrast to supercontinuum-based techniques for long-wavelength generation, the high levels of Raman gain generated at these wavelength bands could produce useful optical amplification necessary for the development of numerous mid-IR laser sources.     

Design of cascading two stages of high gain harmonic generation scheme based on Shanghai deep ultraviolet free electron laser

Cascading stages of high gain harmonic generation free electron laser (FEL) seem to be a feasible way to generate short wavelength radiation. With help of the analytical estimates, we design a two-stage cascading scheme to achieve 131 nm DUV radiation on the basis of the Shanghai deep ultraviolet free electron laser test facility. Detailed studies on the FEL performance, the stability and the sensitivity of the output power to parameter variation have been achieved by GENESIS1.3, and design of the lattice structure is presented.     

Optical characterization of antimony-based bismuth-doped thin films with different annealing temperatures

Antimony-based bismuth-doped thin film,a new kind of super-resolution mask layer,is prepared by magnetron sputtering.The structures and optical constants of the thin films before and after annealing are examined in detail.The as-deposited film is mainly in an amorphous state.After annealing at 170-370℃,it is converted to the rhombohedral-type of structure.The extent of crystallization increased with the annealing temperature.When the thin film is annealed,its refractive index decreased in the most visible region,whereas the extinction coefficient and reflectivity are markedly increased.The results indicate that the optical parameters of the film strongly depend on its microstructure and the bonding of the atoms.     

Design of cascading two stages of high gain harmonic generation scheme based on Shanghai deep ultraviolet free electron laser

Cascading stages of high gain harmonic generation free electron laser (FEL) seem to be a feasible way to generate short wavelength radiation. With help of the analytical estimates, we design a two-stage cascading scheme to achieve 131nm DUV radiation on the basis of the Shanghai deep ultraviolet free electron laser test facility. Detailed studies on the FEL performance, the stability and the sensitivity of the output power to parameter variation have been achieved by GENESIS1.3, and design of the lattice structure is presented.