Quantum-dot cw heterojunction injection laser operating at room temperature with an output power of 1 W

This paper describes a new cw laser with tunnel-coupled vertically aligned InGaAs quantum dots in an AlGaAs matrix with a room-temperature output power of ∼ 1 W at both mirrors. The maximum operating temperature of the heat sink is ∼ 75 °C. Pis’ma Zh. Tekh. Fiz. 23, 51–54 (February 26, 1997)     

Efficient continuous-wave radiatively cooled cr(4+):forsterite lasers at room temperature

Results of a detailed experimental investigation aimed at reducing the thermal loading problem in a cw Cr(4+):forsterite laser at elevated temperatures are presented. From a Cr(4+):forsterite crystal with a differential absorption coefficient of 0.57 cm(-1), as much as 900 mW of cw output power has been obtained at 1.26 mum and at a crystal boundary temperature of 15 degrees C with an absorbed pump power of only 4.5 W at 1.06 mum. No chopping of the pump beam was necessary. An efficient radiative cooling technique was further employed to cool the laser and no subsequent power fading was observed. To the author's knowledge, the measured absorbed power slope efficiency of 29.5% represents the highest cw power performance reported to date from a Cr(4+):forsterite laser pumped by a Nd:YAG laser around room temperature. The role of the low differential absorption coefficient in the reduction of thermal loading is further elucidated by presenting comparative cw power performance data with a second Cr(4+):forsterite crystal having a differential absorption coefficient of 1.78 cm(-1) in the temperature range between 12 and 35 degrees C. Finally, some interesting multipulse effects of the laser observed in the millisecond regime during quasi-cw operation at 50% duty cycle are described.     

808-nm diode-pumped continuous-wave Tm:GdVO4 laser at room temperature

A high-quality gadolinium vanadate (GdVO4) crystal with 7-at. % thulium as the starting material was grown by the Czochralski technique. The measured absorption spectra exhibited sufficient absorption coefficients for laser diodes (LDs) for neodymium laser pumping: 6.0 cm(-1) for pi polarization and 6.2 cm(-1) for sigma polarization at 808 nm. Laser oscillation was carried out with single-stripe 808-nm LDs in an end-pumping configuration. A slope efficiency of 28% and a threshold of 750 mW were exhibited with respect to the absorbed pump power. An output power of 420 mW was achieved at an absorbed power of 2.4 W. It was demonstrated that Tm:GdVO4 is a useful material for 2-microm lasers, particularly in a compact LD-pumped system.     

High efficiency, diode pumped Nd:YAG ceramics slab laser with 230 W continuous-wave output power

Diode pumped zig-zag slab lasers are widely adopted for continuous-wave high power or pulsed high energy applications. Recently [J. Eur. Opt. Soc.-Rapid 6, 11041 (2011)] we started to investigate a new thin slab format in which pumping radiation input is obtained through the thin lateral faces (edge pumping) and the beam propagation takes place bouncing on these same lateral faces ("edge zig-zag"). We report on the optimized operation of a ceramic Nd:YAG laser, based on this geometry, extracting 230 W at a 43% output power to diode power conversion efficiency. Thorough investigation of the thermal lens effect allows us to analyze the optical cavity and thus to define the main aspects limiting the present laser configuration.     

Chromium-doped forsterite: the influence of crystal characteristics on laser performance

A study of the dependence of the gain-switched laser operation of chromium forsterite on crystal parameters is presented. Results are reported for a wide range of chromium (IV) ion concentration: 0.02-0.12 at. % and 12-41 figure of merit, with emphasis on performance of the recently developed material with a dopant level of >0.10 at. %. Threshold and slope efficiency calculations are compared with measured performance for all crystals, with variation of pump polarization and output coupling. With 3% output coupling, the lowest threshold of 1.8 mJ, and highest slope efficiency of 13% were measured for a short, high-dopant-level crystal. With 33% output coupling a slope efficiency of 44% was measured for this crystal. Results demonstrate the considerable potential of short, high-dopant-level crystals for applications such as amplification, diode pumping, and narrow-bandwidth operation.     

Chromium-doped forsterite: dispersion measurement with white-light interferometry

Using a Michelson white-light interferometer, we measure the group-delay dispersion and third-order dispersion coefficients, d2(phi)/d(omega)2 and d3(phi)/d(omega)3, of chromium-doped forsterite (Cr:Mg2SiO4) over wavelengths of 1050-1600 nm for light polarized along both the c and b crystal axes. In this interval, the second-order dispersion for the c axis ranges from 35 fs2/mm to -14 fs2/mm, and the third-order dispersion ranges from 36 fs3/mm to 142 fs3/mm. For the b axis the second-order dispersion ranges from 35 fs2/mm to -15 fs2/mm and the third-order from 73 fs3/mm to 185 fs3/mm. Our data are relevant for the development of optimized dispersion compensation tools for Cr:Mg2SiO4 femtosecond lasers. These measurements help to clarify previously published results and show some significant discrepancies that existed, especially in the third-order dispersion. Our results should furthermore be useful to build up an analytic expression for the index of refraction of chromium forsterite.     

High-power continuous-wave cr(4+):forsterite laser

The temperature and pump power dependence of infrared luminescence of Cr(4+):forsterite are measured. It is demonstrated that temperature-dependent fluorescence in Cr(4+):forsterite is the major reason for saturation of the output power of a continuous-wave laser. At higher pump intensities the temperature rise inside the crystal becomes significant, and even outside cooling does not help to prevent significant reduction of the laser performance. These measurements serve as a guideline to construct a high-power continuous-wave Cr(4+):forsterite laser.     

Multifrequency erbium-doped fiber laser operating at room temperature

A method to realize room-temperature operation of a multifrequency Er-doped fiber laser with low-frequency shift feedback placed within a linear laser cavity is theoretically proposed and experimentally demonstrated. Simultaneous multiwavelength lasing with 0.5 nm wavelength spacing is experimentally demonstrated by applying a sinusoidal signal of 10 kHz to a fiber phase modulator inserted within the linear cavity to prevent single wavelength steady-state oscillation. In the linear cavity, an all-polarization-maintaining fiber Sagnac loop is used as a periodic filter, and a single-mode fiber loop with a polarization controller is used as a partial reflector and also as an output port.     

A semiconductor whispering-gallery-mode laser with ring cavity operating at room temperature

Whispering gallery mode (WGM) semiconductor lasers with ring and disk cavities (outside diameters 300, 200, and 100 μm) operating in a pulsed regime at room temperature on a λ = 2.4 μm wavelength have been created. A comparative study of the spectral and threshold characteristics of these lasers showed that ring lasers operate, like those with the disk cavities, on WGMs. The level of spontaneous emission in the ring lasers is lower by almost an order of magnitude than that in the disk lasers, which is due to the absence of recombination in the central part of the cavity. The threshold current density in ring lasers is slightly greater than that in the disk lasers, which is related to an increase in the current density at the edges of both cavities and to the appearance of surface leak currents on the inner surface of the ring-shaped cavity.     

Quantum-dot injection heterolaser with 3.3 W output power

Continuous-wave lasing has been achieved via the ground state of composite vertically coupled InAlAs/InGaAs quantum dots in an AlGaAs matrix with a room temperature output power of 3.3W at both mirrors. Pis’ma Zh. Tekh. Fiz. 25, 41–46 (June 12, 1999)     

Broadly tunable continuous-wave orange-red source based on intracavity-doubled Cr4+:forsterite laser

The operation of a room-temperature, continuous-wave, intracavity frequency-doubled Cr4+:forsterite laser capable of producing broadly tunable output in the orange-red region of the electromagnetic spectrum is described. Intracavity doubling was achieved in a periodically poled lithium niobate crystal that had gratings with different periods. Tunable second-harmonic output could be obtained between 613 and 655 nm. At a wavelength of 630 nm, intracavity doubling yielded as much as 45 mW of continuous-wave output. To the author's knowledge, this represents the highest second-harmonic-power generation obtained to date with a continuous-wave Cr4+:forsterite laser.     

Generalized formula for continuous-wave end-pumped Yb-doped material amplifier gain and laser output power in various pumping configurations

We present a general formula fitted for computing the amplification and laser output power in a Yb-doped material under various quasi-end-pumping configurations. These configurations include single pass pumping, backreflection pumping in which the pump is reflected by a mirror set on the rear face of the amplifier medium, contrapropagation pumping where two pump beams are launched on both sides of the amplifier and, for every configuration, regenerative pumping in which the transmitted or reflected pump beam is recycled using the proper apparatus. We show that, with regenerative pumping, the efficiency is drastically improved and the optimum amplifier length leading to the maximum laser output power is shorter compared with the one obtained with conventional pumping. In this model, we do not take temperature effect into account.     

调频连续波激光干涉光纤温度传感器

本文提出了一种调频连续波激光干涉非本征型法珀腔光纤温度传感器。使用具有较高热膨胀系数的不锈钢圆管封装法珀腔制成温度传感探头。不锈钢圆管作为法珀腔腔体的同时也是温度敏感元件。通过调频连续波干涉测量技术测量法珀腔因受热膨胀所产生的腔长变化量,实现对温度的传感。实验结果表明,该光纤温度传感器测温分辨率达到了0.0002 ℃,温度测量灵敏度可达3022 nm/℃。此温度传感器不仅具有较高的灵敏度与分辨率,且结构简单稳定,具有良好的应用前景。     

Al-doped ZnO films by pulsed laser deposition at room temperature

Polycrystalline Al-doped ZnO films with good photoluminescence property were successfully deposited on quartz glass substrates by pulsed laser deposition (PLD) at room temperature. The films were obtained by ablating a metallic target (Zn:Al 3 wt%) at various laser energy densities (1.0-2.1 J/cm²) in oxygen atmosphere (9 Pa). The structure of the films was characterized by XRD. Ultraviolet photoluminescence centered at 359-361 nm was observed in the room temperature PL spectra of the Al-doped ZnO films.     

Modulation of the polarization of semiconductor laser radiation at constant output power

The degree of polarization of “doubly”-modulated (by the pump current and the optical confinement factor) laser radiation is analyzed by applying a method of analyzing the stability of the solutions of systems of Lyapunov differential equations to a system of rate equations. An analysis of the system of rate equations yielded its eigenvalues, also called stability coefficients, which are the characteristic time for a transition of the system from one state to another. The behavior of a doubly modulated laser was modeled mathematically and it was demonstrated that the polarization of the laser output radiation can be controlled with almost constant output power. Pis’ma Zh. Tekh. Fiz. 24, 84–90 (August 26, 1998)     

Control of the gas laser output power

The paper considers the influence of a transverse magnetic field on the positive column of a glow discharge on the example of the gas discharge laser. The magnetic field was created using a developed system consisting of several electromagnets and an equalizing device for a greater uniformity of the field. It is shown that as a result of application of the magnetic system charged particles in the discharge gap are shifted to the walls of the discharge tube, which reduces the efficiency of the laser and decreases its output power. Thus, changing the current through the electromagnets the output power of the laser can be varied. The inertia of the impact of the magnetic field on the plasma in the discharge gap was of the order of one millisecond.     

Quantum-dimensional lasers with weak temperature dependence of the output power

An injection laser configuration based on asymmetric quantum-dimensional heterostructure with inhomogeneous excitation of quantum wells (QW) is proposed. This configuration allows one to substantially reduce the temperature dependence of the output power. It is demonstrated that the relative variation of the lasing power at room temperature can be less than 1% per 10°C.     

Determination method of equivalent insulation test voltage at room temperature for high temperature superconducting power apparatus with coil structure

This paper deals with the determination method of the equivalent insulation test voltage at room temperature that secures the reliability of the cryogenic electrical insulation of the high temperature superconducting (HTS) power apparatus. The high voltage test is related to the apparatus with coil structure at the stages of its development, manufacturing and shipment. In the test method, the equivalent insulation test voltage at room temperature is derived from the standard test voltage at cryogenic temperature, based on the idea that the HTS power apparatus should be operated without partial discharges (PDs). The conversion factor between the two voltages is given by the product of the two medium factors, i.e. the one relating to the potential distribution along the coil winding and the other relating to the PD inception condition at the weakest part in the electrical insulation system. In order to determine the latter factor concerned with the non-linear phenomena against electrical stresses, the PD inception voltages at cryogenic and room temperatures are theoretically and experimentally estimated for modeled turn-to-turn insulation system. The results show that both estimated and measured values are in fairly good agreement and the proposed method is useful for the equivalent high voltage test at room temperature for the HTS power apparatus.