High-gain Laser Research Articles

Growth of high-density 1.06-μm InGaAs/GaAs quantum dots for high gain lasers by molecular beamepitaxy

We have progressed the growth procedure for high-density highly-uniform In(Ga)As/GaAs quantum dots (QDs) by using molecular beam epitaxy and have demonstrated high-gain 1.06-μm QD lasers for consumer electronics. The structural and optical properties of QD crystals have been improved by optimizing the growth temperature, employing InGaAs QDs in place of InAs QDs, and utilizing a height-limiting growth method, which is called the Indium-flush procedure. Lasers containing ten-layer height-limited InGaAs QDs provided a net modal gain as high as 60cm−1, which is one of the largest values for InAs/GaAs QD lasers. These results will promise the development of optoelectronic devices with high-density multiply-stacked QDs in the 1-μmband.

High-power near diffraction-limited 1 064-nm Nd:YAG rod laser and second harmonic generation by intracavity-frequency-doubling

We present a near diffraction-limited 1 064-nm Nd:YAG rod laser with output power of 82.3W(M2 \approx 1.38). The power fluctuation over two hours is better than \pm 1.1%. Pulsed 1 064-nm laser with an average power of 66.6 W and pulse width of 46 ns are achieved when the laser is Q-switched at a repetition rate of 10 kHz. The short pulse duration stems from the short cavity as well as the high-gain laser modules. Using intracavity-frequency-doubling, a 35.0-W near diffraction-limited 532-nm green laser (M2 \approx 1.32) is achieved with a pulse width of 43 ns.

Uniqueness and evolutionary status of MWC 349A

AbstractMWC349A, which had remained an ordinary member of the MWC catalog for a few decades, is now known as: (1) the brightest stellar source of radio continuum; (2) the only known high-gain natural maser in hydrogen recombination lines; and (3) the only strictly proven natural high-gain laser (in IR hydrogen recombination lines). These phenomena seem to occur in the circumstellar disk seen almost edge-on. They help us understand the structure and kinematics of the disk. The evolutionary status of MWC 349A is still debated: a young HAeBe star with a pre-planetary disk or an old B[e] star or even a protoplanetary nebula? We discuss new observational data obtained at the Maria Mitchell Observatory and elsewhere which may cast light on this issue.

On the 1.7 μm Fe ii and other natural lasers

We confirm, by numerical modelling, the suggestion by Johansson & Letokhov (JL) that some infrared (IR) transitions of circumstellar Fe ii may be inverted by radiative pumping and can, in principle, act as lasers. In contrast with JL, we show that the inversion of populations can be created directly, by the diluted blackbody continuum of the nearby star, without the intermediacy of trapped Lyα photons. Besides η Car (the target object of the JL model), IR Fe ii lasers should be searched for in other objects with large detected amounts of Fe ii– quasars, supernova remnants, B[e] stars, T Tau stars, etc. However, assuming that the pumping cycle contains radiative steps (the most probable situation for an interstellar or circumstellar medium), we demonstrate that the probability of creating a high-gain natural laser is low (as opposed to the probability of creating a high-gain maser), which can explain the relative scarcity of the detected astrophysical lasers. In particular, the available indirect observational evidence indicates that the gain of the 1.7 μm Fe ii lasers in η Car must be low. IR observations with high spatial and spectral resolution are needed to verify this conclusion.

Detailed characterization of pump-induced refractive index changes observed in Nd:YVO_4, Nd:GdVO_4 and Nd:KGW

The refractive index changes which can be induced in the Nd:YVO(4), Nd:GdVO(4) and Nd:KGW high gain laser crystals, when their Nd(3+) laser active ions are pumped from their ground- to excited- energy levels, have been carefully measured and characterized. By using two complementary optical techniques based on pump-probe interferometry and transient diffraction grating, the electronic and thermal contributions to the observed refractive index variations have been accurately determined and successfully exploited to derive various parameters such as polarizability changes, thermo-optic coefficients and thermal diffusivities.

Stability criteria for spontaneously pulsing gas lasers

Low-threshold spontaneous pulsations are known to occur in the output beams of certain high-gain gas lasers, and good agreement between the experimental observations and numerical models has been achieved. There have also been several analytical studies of threshold criteria for spontaneously pulsing lasers. However, the analytical studies are mostly not applicable to the lasers in which the pulsations have been observed. Stability criteria for high-gain gas lasers are derived in this study, and these criteria are compared with a previously modeled gas laser instability.

High repetition rate laser pulses amplified by Nd/Cr:YAG ceramic amplifier under CW arc-lamp-light pumping

Laser pulses with high repetitive rate generated from a Q-switch microchip Nd:YAG oscillator were amplified by Active mirror composed of Nd/Cr:YAG ceramic pumped by CW arc-lamp. The laser pulses were amplified, and saturation of averaged output laser power was observed. Repetitive ratio of injected laser pulses was changed from 20 to 100 kHz. Averaged output laser power and gain were measured, and gain coefficient and power-extraction efficiency were evaluated. Output laser power was calculated and compared to experimentally measured one, and the calculated results are consistent with the experimental ones. For amplification of laser pulses with high repetitive ratio, this laser material can realize very high laser gain with low pumping power density and high optical–optical conversion efficiency under CW-lamp-light pumping.

Laser pulses amplified by Nd/Cr:YAG ceramic amplifier using lamp and solar light sources

Laser pulses generated in a laser oscillator were amplified by Nd/Cr:YAG ceramic amplifiers. The saturation of output-laser energy was experimentally observed. We found that the stimulated emission cross-section of Nd/Cr:YAG ceramics was effectively increased and the saturation fluence was effectively reduced to 0.1 J/cm 2 due to the energy transfer between excited Cr and Nd ions. The output-laser energy we calculated was compared with the experimental ones and the extractable stored energy in the Nd/Cr:YAG ceramics was evaluated. This laser material is suitable for high-repetition-rate operations because of the high laser gain with low pumping intensity and low effective saturation fluence.

High-gain injection quantum-dot lasers operating at wavelengths above 1300 nm

We have created and studied the properties of semiconductor lasers on InAs/GaAs quantum dots with a maximum modal gain of 46 cm−1 at a wavelength of 1325 nm achieved due to increased optical confinement factor and optimized heterostructure growth parameters. In a wavelength interval of 1315–1345 nm, the modal gain exceeded 20 cm−1 at a current density of 500 A/cm2.

High-gain harmonic generation free electron laser seeded by few-cycle laser

Tunable output wavelength is an important character of a free electron laser (FEL). As generally understood, to alter the wavelength of a high-gain harmonic generation (HGHG) FEL laser, the seed laser must be tunable. A few-cycle, high intensity laser obtained by optical compression usually has pretty broad bandwidth in the spectral domain, which can be used as the seed laser of a HGHG and may open the possibility to approach a HGHG scheme with fully tunable wavelength. In this paper, a HGHG FEL seeded by a few-cycle laser is theoretically discussed and numerically investigated. A few-cycle seed laser significantly influences HGHG FEL performance, especially in output wavelength tuning. For a HGHG FEL seeded by a 4-cycle 786 nm laser, output wavelength tunability range up to 14.9% of the central wavelength 262 nm is observed by adjusting the resonant condition.

Numerical simulation of end-pumped CW Nd3+:GdVO4 laser at 1063 nm

A theoretical model to simulate an end-pumped CW Nd3+:GdVO4 laser at 1063nm is presented. Its essence is to use the propagation equations to demonstrate the spatial evolutions of the pump and the laser powers in the cavity, hence it is applicable to both low and high gain lasers. The simulation results obtained by this model are in good agreement with the experimental observations reported in the literature for a Ti:sapphire-pumped Nd3+:GdVO4 laser. Moreover, some parameters, such as the reflectivity of output coupler, the spot size of laser beam and the crystal length, are discussed with a view to optimizing the laser performance.

Solution viscosity adjustable phloroglucinolcarboxylic acid/formaldehyde applied in extremely thin shell fusion target fabrication

Capsuliform fusion target was prepared by using the OO/W/OI emulsion process. Phloroglucinolcarboxylic acid / formaldehyde (PF) is expected to be used as the water phase (W) solution which then gelates to be the shell of the capsule. The density of the shell should be low to obtain high laser gain. Phloroglucinolcarboxylic acid had addition and condensation reaction with formaldehyde under basic condition to form linear polymer first. The nano-scale linear polymers were then linked via noncovalent interactions, such as hydrogen bonding, van der Waals, to continue the gelation process. The type and amount of the base catalyst used in the reaction can affect the polymerization of PF, including the gelation rate and gelation concentration. By changing the basic condition of the reaction, the proper viscosity of 9×10−5 for capsuliform target fabrication was reached and extremely thin gel shell thickness of 17μm with low polymer concentration of 26.3mg/cm3 was obtained.

High-gain direct-drive laser fusion with indirect drive beam layout of Laser Mégajoule

A new solution for high-gain direct-drive fusion with the indirect drive beam irradiation of the Laser Mégajoule is presented here. This solution uses 2 rings per hemisphere at polar angles of 49° and 59.5°. The 2D calculations with the hydrodynamics code FCI2 lead to a thermonuclear energy of 32 MJ with less than 1 MJ incident laser energy.

Spontaneous mode locking in mixed-broadened laser oscillators

A theoretical model is reported for spontaneous mode locking in mixed-broadened laser oscillators. Experimental observations of this effect have been available for many years, but no rigorous interpretation has been given. Numerical calculations emphasize the case of a high-gain xenon laser, for which extensive experimental data have been published. Complex pulsation characteristics are observed as the cavity length and pumping rate are varied, and the theoretical results are in good agreement with the experimental data.

Diffractive optical elements for high gain lasers with arbitrary output beam profiles

We introduce a previously unreported laser cavity configuration, using a diffractive optical element (DOE) in place of the output coupler. Such a configuration allows the DOE to work both in reflection, as a mode shaping element, and in transmission as a beam shaper. Employing dual wavelength DOE optimization techniques and phase delays greater than 2pi, allows the two functions to be designed independently. Thus, an arbitrary output beam profile can be combined with a mode shape which maximizes energy extraction from the gain medium. Devices are designed and their performance modeled for a 1m cavity with 5mm diameter mirrors and a wavelength of 632.8nm. An element with 32 quantization levels and a maximum phase delay of 8pi in transmission produces high quality results.

Scattering of vacuum states by dynamic plasmon singularities: generating photons from vacuum

A metallic nanoparticle surrounded by an amplifying medium results in a boundary condition that creates a singularity in the particle's dynamic polarizability at a critical value of the gain. When this boundary condition is time dependent, parametric excitation of the electromagnetic vacuum results in photon emission. Estimates of the vacuum emission from nanostructures embedded in high-gain laser dyes excited by femtosecond lasers predict energies nearly 2 orders of magnitude larger than the spontaneous emission background.

Design and Demonstration of Novel QW Intermixing Scheme for the Integration of UTC-Type Photodiodes With QW-Based Components

We present the design and demonstration of unitraveling carrier (UTC) photodiodes fabricated using a novel quantum-well (QW) intermixing and metal-organic chemical vapor deposition (MOCVD) regrowth fabrication platform. The photodiodes discussed here were realized on the same chip as high gain centered QW active regions, intermixed passive centered well waveguides, and low optical confinement offset QW active regions regrown over intermixed wells. This demonstration lifts previous constraints imposed on high functionality photonic circuits, which forced a common waveguide architecture in the detector, laser, and amplifier by validating a platform suited for the monolithic integration of UTC photodiodes into photonic integrated circuits comprised of widely tunable high gain laser diodes, high efficiency modulators, and low optical confinement high saturation power semiconductor optical amplifiers. In this manuscript we focus on the design and performance of UTC photodiodes fabricated on intermixed QWs using this novel scheme. The photodiodes exhibit /spl sim/90% internal quantum efficiency, excellent photocurrent handling capabilities, and minimal response roll-off over the 20 GHz of our testing capability. The 40 Gb/s operation was achieved with the demonstration of open eye diagrams.

High-gain and low-threshold InAs quantum-dot lasers on InP

InAs quantum-dot (QD) laser structures are grown on (113)B-oriented InP substrate by gas-source molecular-beam epitaxy. Following an optimized growth procedure, a high density of 1.1×1011cm−2 of uniformly sized QDs is achieved. Broad-area lasers containing three stacked QD layers have been realized and tested. Laser emission on the ground-state transition (λ=1.59μm) is obtained at room temperature (RT), at a threshold current density as low as 190A∕cm2. Ground-state modal gain and transparency current density is measured to be 7cm−1 and 23A∕cm2 per dot layer. Ground-state laser emission is also demonstrated from low temperature (100 K, Jth=33A∕cm2) to high temperature (350 K), exhibiting an insensitive threshold in the [100, 170] K range, and a 55 K characteristic temperature at RT.

Demonstration of high saturation power/high gain SOAs using quantum well intermixing based integration platform

The performance of semiconductor optical amplifiers (SOAs) employing regions of high and low optical confinement designed for high saturation power and high gain using a novel quantum well intermixing and MOCVD regrowth fabrication scheme is reported. The scheme enables the monolithic integration of high performance SOAs with high gain laser diodes, high efficiency electroabsorption modulators, and high saturation power photodiodes. The SOAs presented exhibit saturation powers in the 19 to 20 dBm range with nearly 15 dB of gain.

Quantum well intermixing and MOCVD regrowth for monolithic integration of 40 Gbit/s UTC type photodiodes with QW based components

A novel fabrication method for uni-travelling carrier (UTC) type photodiodes using quantum well (QW) intermixing and MOCVD regrowth is presented. This scheme will enable the monolithic integration of the photodiodes with high gain laser diodes, high efficiency electroabsorption modulators, and high saturation power semiconductor optical amplifiers. The photodiodes fabricated on intermixed quantum wells presented exhibit excellent photocurrent handling capabilities, minimal response roll-off over the 20 GHz of the testing capability, and open 40 Gbit/s eye diagrams.