Laser-pumped Laser Research Articles

External magnetic field effect on the growth rate of a plasma-loaded free-electron laser

In order to extend the production of intense coherent radiation to angstrom wavelengths, a laser wave is employed as a laser wiggler which propagates through a magnetized plasma channel. The plasma-loaded laser wigglers increase the ability of laser guidance and electron bunching process compared to the counterpropagating laser wigglers in vacuum. The presence of the plasma medium can make it possible to propagate the laser wiggler and the electron beam parallel to each other so that the focusing of the pulse will be saved. In addition, employing an external guide magnetic field can confine both the ambient plasma and the transverse motions of the electron beam, therefore, improving the free-electron lasers’ efficiency, properly. Electron trajectories have been obtained by solving the steady state equations of motion for a single particle and the fourth-order Runge-Kutta method has been used to simulate the electron orbits. To study the growth rate of a laser-pumped free-electron laser in the presence of a plasma medium, perturbation analysis has been performed to combine the momentum transfer, continuity, and wave equations, respectively. Numerical calculations indicate that by increasing the guide magnetic field frequency, the growth rate for group I orbits increases, while for group II and III orbits decreases.

Structure and spectral properties of Nd3+-doped KBaGd(MoO4)3 crystal with a disorder structure

In order to obtain new, more efficient laser materials for diode laser-pumped lasers, the laser host materials with broad absorption bands are very important. This paper reports the structure and spectral properties of Nd3+ : KBaGd(MoO4)3 crystal. KBaGd(MoO4)3 crystallizes in the monoclinic system with space groupC2/c. The structure analysis shows that KBaGd(MoO4)3 crystal has a disordered structure. The investigation of the spectral properties of Nd3+ : KBaGd(MoO4)3 crystals shows that it exhibits broad absorption and emission bands, which are caused by the disordered structure of the KBaGd(MoO4)3 crystal. The broad absorption band is very suitable for diode laser pumping. To sum up the spectral properties of Nd3+ : KBaGd(MoO4)3 crystal, it may be regarded as a potential solid-state laser material for diode laser pumping.

Development of a full spatial coherent X-ray laser at 13.9�nm

We have succeeded in developing a laser-pumped X-ray laser with full spatial coherence at 13.9 nm. The X-ray laser beam with a very small divergence of 0.2 mrad was generated from double target experiments, where a seeding light from the first laser medium was amplified in the second laser medium. The observed divergence was close to the diffraction limit value within a factor of two. The seeding light was amplified in the second medium without refraction influence and the gain coefficient was 7.9 cm-1. From the measurement of visibility, it was found that the spatial coherent length was longer than the beam diameter.

Laser performance and spectroscopic properties of Nd3+-doped LiKYF5 and LiKGdF5 crystals

Spectroscopic and laser-pumped laser studies of Nd3+-doped LiKYF5 and LiKGdF5 are reported. The optical absorption and photoluminescence spectra are strongly polarised, the sense of polarisation of the 4I92 → 2F52, 2H92 absorption near 800 nm being opposite to that of the 4F32 → 4I112 laser emission near 1.05 μ. At ambient temperature (∼ 300 K) the luminescence decay times of excited Nd3+ ions are in both hosts of order 480–490 μs, and strongly concentration dependent above 2 at.% Nd3+. Efficient laser action (∼ 25%) is observed under excitation with a long pulse Cr3+: LiSAF laser tuned to 797 nm, with low threshold energies of ca. 125 μJ.

Multiple harmonic generators for improved efficiency of laser-pumped lasers

A multistage system of three second-harmonic-generating crystals has been used to improve the total conversion efficiency from the fundamental at 1.06 mum to the second harmonic at 532 nm. Demagnifying telescopes placed into the path of the residual fundamental light, after chromatic separation of the second harmonic, allow further second-harmonic crystals to be used. More than 97% conversion has been obtained from 207-mJ, Q -switched Nd:YAG laser pulses at 1.06 mum, producing more than 201 mJ at 532 nm. Good agreement is achieved between experiment and theory for the spatial and temporal evolution of the second-harmonic beams at each stage.

Transition metal-doped zinc chalcogenides: spectroscopy and laser demonstration of a new class of gain media

The absorption and emission properties of transition metal (TM)-doped zinc chalcogenides have been investigated to understand their potential application as room-temperature, mid-infrared tunable laser media. Crystals of ZnS, ZnSe, and ZnTe, individually doped with Cr/sup 2+/, Co/sup 2+/, Ni/sup 2+/, or Fe/sup 2+/ have been evaluated. The absorption and emission properties are presented and discussed in terms of the energy levels from which they arise. The absorption spectra of the crystals studied exhibit strong bands between 1.4 and 2.0 /spl mu/m which overlap with the output of strained-layer InGaAs diodes. The room-temperature emission spectra reveal wide-band emissions from 2-3 /spl mu/m for Cr and from 2.8-4.0 /spl mu/m for Co, Cr luminesces strongly at room temperature; Co exhibits significant losses from nonradiative decay at temperatures above 200 K, and Ni and Fe only luminesce at low temperatures, Cr/sup 2+/ is estimated to have the highest quantum yield at room temperature among the media investigated with values of /spl sim/75-100%. Laser demonstrations of Cr:ZnS and Cr:ZnSe have been performed in a laser-pumped laser cavity with a Co:MgF/sub 2/ pump laser. The output of both lasers were determined to peak at wavelengths near 2.35 /spl mu/m, and both lasers demonstrated a maximum slope efficiency of approximately 20%. Based on these initial results, the Cr/sup 2+/ ion is predicted to be a highly favorable laser ion for the mid-IR when doped into the zinc chalcogenides; Co/sup 2+/ may also serve usefully, but laser demonstrations yet remain to be performed.

Investigation of the laser properties of Cr/sup 3+/:LiSrGaF/sub 6/

A boule of Cr:LiSGAF (Cr/sup 3+/:LiSrGaF/sub 6/), the Ga analog of Cr:LiSAF, was grown, a laser sample was fabricated, and its efficiency was measured using a laser-pumped laser configuration. The laser performance near 820 nm and related properties of Cr:LiSGAF are reported. The use of Sr instead of Ca results in a red shift of the absorption and emission band (along with an increase in the emission cross section). Insight into the effect of a change in the identity of the substitutional site on the properties of the laser is provided. >

Alexandrite-laser excitation of a Tm:Ho:Y_3Al_5O_12 laser

Laser-pumped laser characteristics of a Tm:Ho:Y3Al5O12(YAG) crystal were measured as a function of the wavelength and energy of the alexandrite-laser pump source. Laser thresholds and slope efficiencies were recorded for 765-, 780-, and 785-nm pump wavelengths. Simultaneous laser emission was observed at 2.060, 2.065, 2.097, and 2.101 μm, and the relative intensities of these peaks were measured as a function of absorbed pump energy. Changes in temporal and spectral profiles of the laser emission were observed with variations in absorbed pump energy. When measurements were made with a monolithic crystal cavity instead of an open cavity, laser emission from Ho3+ was observed at 2.097 μm, and an additional laser peak was observed that may be due to transitions of the Tm3+ ions.

Site-selection spectroscopy, energy transfer, and laser emission in Nd3+-doped Ba2MgGe2O7

A detailed spectroscopic and pump wavelength dependent laser study has been performed on Nd3+ ions in Ba2MgGe2O7. Site-selection spectroscopy experiments reveal fifteen distinct crystal field sites for the Nd3+ ions. At room temperature, excitation of ions in any one of these sites is followed by efficient, thermally activated energy transfer to ions in a site having a laser emission transition at 1054 nm. Laser-pumped laser experiments were performed to determine the pumping threshold and slope efficiency of laser action in this material for different monochromatic pump wavelengths. The measured slope efficiencies were found to be pump wavelength dependent and ranged from 6% to 22%. Excited-state absorption of pump photons was shown to be responsible for this variation in the slope efficiency.

Bragg reflection by a gain medium optically pumped in a grating geometry

The utilization of Bragg reflection caused by a grating-like pump intensity distribution in a laser-pumped laser amplifier is analyzed theoretically. In the amplifier, an incident laser beam is split into a transmitted and reflected beam, both of which are amplified. We explicitly take into account the interference between the transmitted and reflected beam and the effect of the interference on the saturated gain. We determine the reflective conversion efficiency of such an amplifier and show that if the gain grating is accompanied by a pump-heating-induced refractive-index grating, the reflective conversion efficiency may approach 100 percent.

On some properties of axicons

The radial and axial pump power distribution in the line focus of a cone (as simplest example of an axicon) is discussed. It is also shown that four conical surfaces covered with antireflection coatings can make an efficient polarizer for radial and tangential polarization of a light beam. Glass cones can be used as efficient pump optics for laser-pumped lasers. The advantages of the novel pumping scheme are discussed in detail for the cases of dye-laser and x-ray laser pumping.

An investigation of the Co:MgF2laser system

The Co:MgF <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> laser, tunable over the range from 1.5 to 2.3 μm, has been investigated under a variety of operating conditions. Included in this paper are reports on basic spectroscopy of Co:MgF <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> , a determination of the gain cross section, the efficiency and temporal behavior under pulsed excitation, and performance in the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</tex> -switched mode. In addition, operation with thermoelectric cooling and CW oscillation at the multiwatt power level are discussed. Equations covering laser-pumped lasers are derived and comparisons between experiments and theory are presented.

Instabilities in laser-pumped gas lasers: experimental oscillation line shapes

Heterodyne measurements are presented of the above-threshold oscillation spectrum of several optically pumped molecular lasers under a variety of conditions. The data suggest that, under some conditions, single-mode sideband instabilities resulting from two-photon susceptibilities could dominate.

Laser-pumped molecular laser

The parameters of laser-pumped molecular lasers are investigated. It is established that the energy and tuning characteristics of an NH3 laser (Eg = 1.5 J, efficiency 20%, Pav = 20 W, radiation frequency tuning band 753–890 cm-1) are decisively influenced by the addition of N2. A focusing raster optical-pumping system has made it possible to obtain a specific lasing energy 12 J/liter. A CF4 laser with lasing energy 40 mJ operates in the 612–655 cm-1 band. Experiments on dissociation of the molecules CCl4 and UF6 were carried out with the aid of NH3 and CF4 lasers. The systems and methods of producing Raman lasers (RL) are presented. An effective RL amplifier on rotational transitions in compressed H2, which transforms tens of beams of Nd lasers into one coherent beam of the first Stokes component with λ ≅ 1.13 μm at an efficiencyup to 70%, is described.

Stark effect in the CO 2 laser-pumped CH 3OH far-infrared laser as a technique for high-resolution infrared spectroscopy

The potential of the Stark effect as a method for assigning far-infrared emission lines observed in infrared laser-pumped lasers is examined. The technique is applied to previously unassigned lines in CO 2 laser-pumped CH 3OH. Seventeen lines are shown to form an interrelated pattern and on the basis of combination relations a set of energy levels is identified which is not predicted by current models for the vibrationally excited CH 3OH molecule.

Laser-pumped molecular lasers - Part II: Submillimeter laser experiments

We report the first experimental determination of the gain spectrum of a laser-pumped submillimeter laser amplifier. Single-mode pump and submillimeter oscillators were used to determine the gain as a function of submillimeter laser frequency, pump intensity, relative polarization, and molecular gas pressure. The 385 μm transition in D 2 O and the 496 μm transition in CH 3 F, both pumped by a CO 2 laser, were investigated. The use of single-mode lasers allows a direct comparison with theory. Good agreement is obtained with our recent theory which takes into account two photon contributions to the gain as well as space orientation ( M -level) molecular degeneracy.

Determination of optical cross sections by the measurement of saturation flux using laser-pumped laser oscillators

A new method is reported which measures transition cross sections independent of active atom concentration and extrinsic loss using a laser-pumped cw laser oscillator. Extrapolation of the linear input-output characteristic of a cw oscillator to null pumping rate will yield the saturation power from which is determined the saturation flux and laser cross section. For Nd3+ in YAG and YVO4 the measured saturation fluxes were 2.07 and 3.24 kW/cm2, respectively, and the laser cross sections were 3.92 and 7.78 × 10−19 cm2, respectively.