High Power CW Research Articles

Parametric four-wave mixing using a single cw laser

Four-wave mixing can be used to generate coherent output beams, with frequencies difficult to acquire in commercial lasers. Here, a single narrow external cavity diode laser locked to the two photon 5s-5d transition in rubidium is combined with a tapered amplifier system to produce a high power cw beam at 778 nm and used to generate coherent light at 420 nm through parametric four-wave mixing. This process is analyzed in terms of the intensity and frequency of the incoming beam as well as the atomic density of the sample. The efficiency of the process is currently limited when on resonance due to the absorption of the 420 nm beam, and modifications should allow a significant increase in output power.

Feeding System of a High-Frequency Accelerating Cavities of the Novosibirsk Microtron-Recovery Unit for The Fel. Divider of a High CW Power on the Basis of a Rectangular Waveguide

The article is devoted to the system of the Radio Frequency power transfer and distribution between accelerating cavities of the ERL for FEL of the Siberian center of SR and THz Radiation, SB RAS, Novosibirsk. The system of dividing is built on the basis of a rectangular waveguide, associated with each cavity of a coaxial line by the coaxial-to-waveguide adapter (CWA). It is shown that under a certain choice of waveguide sizes and CWA, the equivalent circuit of the CWA can be represented by a current source. The analysis of the properties of such a system has been carried out and shown its advantages. Also it is discussed the experimental results and the experience of the operation of the device. The article presents the basic design parameters of a waveguide divider 600 kW of continuous power, running at a frequency of 180.4 MHz

High-power cw laser bars of the wavelength range

We have developed the effective design of semiconductor heterostructures, which allow one to fabricate cw laser diodes emitting in the spectral range. The optimal conditions for fabrication of GaAsP/AlGaInP/GaAs heterostructures by MOCVD have been determined. It is shown that the use of quantum wells with a precisely defined quantity mismatch reduces the threshold current density and increases the external differential efficiency. The results of studies of characteristics of diode laser bars fabricated from these heterostructures are presented.

Generating a 2.4-W cw Green Laser by Intra-Cavity Frequency Doubling of a Diode-Pumped Nd:GdVO4 Laser with a MgO:PPLN Crystal

High-power cw green laser radiation is generated by intra-cavity frequency doubling of a diode-pumped Nd:GdVO4 laser with a MgO-doped periodically-poled LiNbO3 (MgO:PPLN) crystal at room temperature. An average power of 2.4 W at 0.53 μm is obtained under the pump 15 W at 808 nm, corresponding to an overall optical-to-optical conversion efficiency of 16%. The M2 factor of the green beam is 3.90 and 1.34 for the horizontal and vertical direction, respectively. In addition, the power fluctuation is measured to be about ±5%.

ICEPIC Simulation of a Strapped Nonrelativistic High-Power CW UHF Magnetron With a Solid Cathode Operating in the Space-Charge Limited Regime

This paper presents the results of particle-in- cell (PIC) simulations of a strapped nonrelativistic ultrahigh- frequency (890-915 MHz) magnetron whose geometrical and operational parameters are close to the parameters of the high- power industrial heating magnetron producing 75-100 kW of continuous-wave microwave power. Simulations of the magnetron operation are performed without artificial RF priming, but rather in natural conditions, when magnetron oscillations start to grow from electromagnetic “noise.” This approach reveals many important details of the “preoscillating” phase of the magnetron operation. It is found, for example, that the start-up time of the magnetron with a solid cathode, operating in the explosive electron emission mode, is determined by the time needed for the electron cloud formed near the cathode to reach the anode, where the fringing dc electric fields of the periodic anode structure begin to perturb the electron cloud and to facilitate the magnetron oscillations to start to grow. The PIC simulations are performed at one magnetic held (0.238 T) and a range of applied voltages, allowing the magnetron to operate in the π mode characterized by five magnetron spokes and T E51-like mode of the induced electromagnetic held distribution within the resonant system of the ten-cavity magnetron.

High-power efficient cw and pulsed lasers based on bulk Yb : KYW crystals with end diode pumping

End-diode-pumped lasers based on one and two Yb : KYW crystals operating in cw and Q-switched regimes, as well as in the regime of mode-locking, are studied. The single-crystal laser generated stable ultrashort (shorter than 100 fs) laser pulses at wavelengths of 1035 and 1043 nm with an average power exceeding 1 W. The average output power of the two-crystal laser exceeded 18 W in the cw regime and 16 W in the Q-switched regime with a slope efficiency exceeding 30 %.

Continuous wave and mode-locked Yb^3+:Y_2O_3 ceramic thin disk laser

CW and mode-locked laser operation based on an Yb3+:Y2O3 ceramic thin disk is reported. In CW laser operation, an output power of 70 W with an optical-to-optical efficiency of 57.4% was achieved. A higher slope efficiency of 70% was also obtained with a 50-W pump laser diode with more suitable emission characteristics. In mode-locked laser operation, pulses as short as 547 fs with an average power of 7.4 W were obtained. To our knowledge, this is the first demonstration of a high power CW and mode-locked laser operation based on Yb3+:Y2O3 ceramic thin disks.

Stabilized high-power laser system for the gravitational wave detector advanced LIGO

An ultra-stable, high-power cw Nd:YAG laser system, developed for the ground-based gravitational wave detector Advanced LIGO (Laser Interferometer Gravitational-Wave Observatory), was comprehensively characterized. Laser power, frequency, beam pointing and beam quality were simultaneously stabilized using different active and passive schemes. The output beam, the performance of the stabilization, and the cross-coupling between different stabilization feedback control loops were characterized and found to fulfill most design requirements. The employed stabilization schemes and the achieved performance are of relevance to many high-precision optical experiments.

Surface reconstruction of porous substrates in sintered bronze by cw-high power diode laser

The present investigation deals with the application of a continuous wave-high power diode laser to modify the surface of porous substrates made from spherical particles in sintered bronze. In particular, the influence of laser power and interaction time on the capability of the laser processing to restructure the substrate morphology was investigated. Scanning Electron Microscope (SEM) and contact-gage surface profiler were used to analyze the evolution of the substrate morphology after laser treatments, whilst their mechanical properties were evaluated by micro-hardness and scratch tests.The experimental findings showed a decrease in the surface roughness of the porous substrates after laser treatments of ∼70%. In addition, an improvement in micro-hardness, scratch and wear resistance could also be achieved. Indeed, large laser power combined with high scan speed took to the most attractive results, thus favoring the onset of a promising morphological structure and the establishment of improved hardness and scratch resistance.

High-power solid-state cw dye laser

In the present paper we describe a high-power tunable solid-state dye laser setup that offers peak output power up to 800 mW around 575 nm with excellent long-time power stability and low noise level. The spectral width of the laser emission is less than 3 GHz and can be tuned over more than 30 nm. A nearly circular mode profile is achieved with an M(2) better than 1.4. The device can be integrated in a compact housing (dimensions are 60 × 40 × 20 cm(3)). The limitation of long-time power stability is mainly given by photo decomposition of organic dye molecules. These processes are analyzed in detail via spatially resolved micro-imaging and spectroscopic studies.

Optical characterization of thermal lens effect in ethanol and the influence of focusing lens and liquid cell size

A high power cw laser beam propagating in an absorbing medium spreads, distorted or deflected as a result of thermally self-induced refractive index gradients. In this paper, optical characteristic of thermal lens effect in liquid ethanol was studied experimentally. The thermal lens was induced by focusing of a high power He–Ne laser beam in ethanol (absorbing liquid). The thermal lens effect was investigated by Z-scan method. Depending on the focusing position of the beam in liquid cell, the results show both intensity increasing and decreasing on a screen, which is fixed at a specific position with respect to the cell. The results show such effects depend on the lens focal length, the liquid cell size, and the focusing position of the lens. According to the results there is a competition between focusing and defocusing of the transmitted beam if the position of the focusing region inside the sample cell is changed. Using a simple optical description, the experimental results were interpreted.

Study on the periodic oscillation of plasma/vapour induced during high power fibre laser penetration welding

High power fibre lasers have recently received much attention because of their inherent advantages such as high output power, high beam quality, compact size, and flexible fibre delivery. Studies on the mechanism behind fibre laser welding systems may further promote their practical application. In this paper, high speed video observations were used to study the characteristics of the plasma/vapour induced during the bead-on-plate welding of ZL114 using a high power CW fibre laser. We also analysed the cause of the periodic oscillation of the plasma/vapour. The results revealed that plasma/vapour induced from high power lasers oscillate periodically at 450–600 μs cycles above the weld pool surface. The use of a shielding gas has little effect on the oscillation cycle. The plasma/vapour absorption is not the main reason for the periodical oscillation of plasma/vapour induced during fibre laser welding. The periodic oscillation of the plasma/vapour can be attributed to the oscillation of the keyhole.

Numerical modeling of thermal effects in a high-power injection-locked cw Ti:sapphire laser

With the FEA and matrix methods, the thermal lenses induced by the thermooptic effect, thermally induced mechanical strain and end face bulging in a Ti:sapphire crystal are analyzed. The results show that there is an unignorable strain-induced lens in a high pump power region. With the thermal lens effect, an injection-locked cw Ti:sapphire laser is numerically simulated. We find that the poor mode matching between the lasing and pump beams due to thermal lens will cause the slope efficiency decreasing. The calculated results agree with the reported experimental data, and we also predict that the thermal lens is obviously active at a certain pump power level.

Internal resonantly enhanced frequency doubling of continuous-wave fiber lasers

In this Letter we describe a simple method for frequency doubling in high-power CW fiber lasers that offers the prospect of very high conversion efficiency and high power in the visible wavelength regime. Our approach is based on second harmonic generation in an enhancement resonator within the fiber laser cavity and does not require active cavity length stabilization. This technique has been applied to a cladding-pumped Yb-doped fiber laser to generate 19 W of linearly polarized CW green output at 540 nm, with excellent temporal stability for 90 W of absorbed diode pump power at 975 nm. The prospects for further improvement in performance with respect to conversion efficiency and output power are considered.

Modeling, numerical approach, and power scaling of alkali vapor lasers in side-pumped configuration with flowing medium

Diode alkali vapor lasers (DPALs) with a flowing medium provide a pathway to extremely high-power CW or quasi-CW laser operations. In this article, the model for end-pumped alkali lasers [Beach et al., J. Opt. Soc. Am. B 21, 2151(2004)] is expanded to model DPALs in a side-pumped configuration. The difference between our model and the published model [Komashko et al., Proc. SPIE 7581, 75810H-1 (2010)] is studied, and a comparison with other people’s experimental results [Zweiback et al., Proc. SPIE 7915, 791509-1 (2011)] is made, which demonstrates the validity of our model. Some important influencing factors are simulated and analyzed. A conceptual power-scaled design of a megawatt-class side-pumped flowing DPAL is made. The results demonstrate an optical-to-optical efficiency over 60% with all the other parameters reasonable and available in the near future.

New high power CW test facilities for ITER ICRH components testing

First CW test bed, devoted for ion cyclotron resonance heating (ICRH), is being built at CEA Cadarache. It has been designed for testing the ICRH antenna sub assemblies under ITER relevant conditions (vacuum, cooling and RF). This paper presents a technical overview of these facilities and discusses their future operations in the framework of the ITER ICRH European R&D program.

First demonstration and performance of an injection locked continuous wave magnetron to phase control a superconducting cavity

The applications of magnetrons to high power proton and cw electron linacs are discussed. An experiment is described where a 2.45 GHz magnetron has been used to drive a single cell superconducting cavity. With the magnetron injection locked, a modest phase control accuracy of 0.95\ifmmode^\circ\else\textdegree\fi{} rms has been demonstrated. Factors limiting performance have been identified.

A continuous wave SrMoO_4 Raman laser

We demonstrate a cw, laser diode-pumped Nd:GdVO4/SrMoO4 crystalline Raman laser. First Stokes laser output at 1173.5 nm of 2.18 W was achieved with a diode-to-first Stokes efficiency of 8.7%. With intracavity frequency doubling in LiB3O5, 3.1 W of cw yellow emission at 586.8 nm was obtained with a 12.4% diode-to-yellow efficiency. The experimental results show that SrMoO4 is an excellent stimulated Raman scattering gain material for high-power cw near-IR Stokes and yellow lasers.

Computational fluid dynamic modeling of gas flow characteristics of the high-power CW CO2 laser

Computational fluid dynamic modeling of gas flow characteristics of the high-power CW CO2 laser

高功率轴快流CO2激光器的流体动力学模拟

To increase the photoelectronic conversion efficiency of the single discharge tube and to meet the requirements of the laser cutting system, optimization of the discharge tube structure and gas flow field is necessary. We present a computational fluid dynamic model to predict the gas flow characteristics of high-power fast-axial flow CO2 laser. A set of differential equations is used to describe the operation of the laser. Gas flow characteristics, are calculated. The effects of gas velocity and turbulence intensity on discharge stability are studied. Computational results are compared with experimental values, and a good agreement is observed. The method presented and the results obtained can make the design process more efficient.