CdS Laser Research Articles

Robust single-mode lasers based on hexagonal CdS microflakes

We have achieved single-mode whispering-gallery-mode lasing in CdS microflakes with sharp linewidth (∼0.12 nm) and high quality factor (∼4200). Such lasers are superior to previous CdS lasers in these lasing parameters. Through time-resolved photoluminescence measurements, electron–hole plasma recombination is established to be the lasing mechanism. The radiative recombination rate of CdS microflakes is enhanced by a factor of ∼4.7 due to the Purcell effect.

Coupled-Mode Theory for Semiconductor Nanowires

We present a model to describe the spatiotemporal evolution of guided modes in semiconductor nanowires based on a coupled mode formalism. Light-matter interaction is modelled based on semiconductor Bloch equations, including many-particle effects in the screened Hartree-Fock approximation. Appropriate boundary conditions are used to incorporate reflections at waveguide endfacets, thus allowing for the simulation of nanowire lasing. We compute the emission characteristics and temporal dynamics of CdS and ZnO nanowire lasers and compare our results both to Finite-Difference Time-Domain simulations and to experimental data. Finally, we explore the dependence of the lasing emission on the nanowire cavity and on the materials relaxation time.

Continuous-wave broadly tunable high-power Cr:CdS laser.

We report spectroscopic characteristics and laser properties of the mid-infrared active laser medium Cr2+:CdS. Temperature-dependent absorption, luminescence and lifetime measurements of the 5E exited state allow determination of peak emission cross section value of 1.35 × 10−18 cm2 in σ-polarization at room temperature. Lifetime values vary from 7.6 µs at 8 K to 0.48 µs at 320 K, corresponding to 22 % quantum yield at 285 K. Under Tm-fiber laser pumping, the continuous-wave output reached 1.8 W at 2.5 μm with 35.5 % slope efficiency. With a single CaF2 prism, the CW Cr2+:CdS laser could be tuned from 2.240 to 3.285 µm.

Room‐temperature tunable mid‐infrared lasers on transition‐metal doped II–VI compound crystals grown from vapor phase

AbstractSeeded free growth method with physical transport was used for preparation of large‐size II–VI single crystals uniformly doped by transition metals directly during the growth. The grown crystals possess small intrinsic losses. Based on these crystals new results on development of mid‐IR lasers were achieved. With the CdSe:Cr crystal pumped at the room temperature (RT) by a continuous wave (CW) 1.908‐µm thulium fiber laser, output laser power at 2.6 µm was increased up to 1.7 W. CW lasing from the ZnSe:Fe crystal was achieved using the 2.97‐µm CW Cr2+:CdSe laser as a pump source. In this case the output power as high as 0.2 W was obtained at 4.1 µm and T = 80 K. Broad spectral tuning of the Cr2+:CdSe (2.26–3.61 µm) and Fe2+:ZnSe (3.95–5.05 µm) lasers was achieved at RT in the pulsed operation. The RT laser action from CdS:Cr and CdSe:Fe was demonstrated for the first time. The output power of the CW Cr+2:CdS laser was 0.81 W. The pulsed Fe2+:CdSe laser was tuned in the 4.6–5.9 µm spectral range.

Cr2+:CdS crystal as a new material for room‐temperature tunable mid‐infrared lasing

AbstractBy using the seeded physical vapour transport (SPVT) method the CdS:Cr single crystals were grown. Doping concentration up to 5×1018 cm‐3 was achieved. The emission lifetime of the exited state, 5E, of Cr2+ in CdS host was measured to be 0.93 μs at room temperature and 7.3 μs at liquid nitrogen temperature. The measured values of peak absorption and emission cross sections were found to be 1.4×10‐18 and 1.1×10‐18 cm2 respectively. Tuning possibility and efficiency of pulsed Cr2+:CdS laser was described. CW laser operation with slope efficiency of 52% and output power up to 0.79 W was obtained (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Continuous-wave Cr2+:CdS laser

Continuous-wave lasing is obtained for the first time in a Cr2+:CdS crystal pumped by a thulium fibre laser at 1908 nm. The output power of the laser at 2534 nm achieved 0.81 W with the slope efficiency with respect to the absorbed pump power equal to 52.3%. The parameters of Cr2+:CdS and Cr2+:CdSe lasers are compared. A Cr2+:CdSe crystal generated 1.7 W of cw radiation at 2638 nm with the slope efficiency with respect to the absorbed power equal to 53.4%.

Pulsed broadly tunable room-temperature Cr2+:CdS laser

We report the spectroscopic characteristics and laser properties of Cr2+:CdS. The emission lifetime of the exited state, 5E, of Cr2+ in CdS host was measured to be 0.93 µs at room temperature and 7.3 µs at liquid nitrogen temperature. The measured values of peak absorption and emission cross sections were found to be 1.4×10−18 and 1.1×10−18 cm2 respectively. Room-temperature pulsed-laser operation was obtained under pumping by the 1.94 µm output of a Tm:YAP laser. The output of the free-running Cr2+:CdS laser was centered at ∼2.6 µm, and an absorbed energy slope efficiency of 38.8% was demonstrated. The passive crystal losses were measured to be less than 0.049 cm−1 at the lasing wavelength. With an intracavity prism, the Cr2+:CdS laser was tuned from 2.18 to 3.32 µm.

Vapor growth of CdSe:Cr and CdS:Cr single crystals for mid-infrared lasers

Single crystals of CdSe:Cr and CdS:Cr with the doping level up to 10 19 cm −3 were grown by a vapor phase contact-free technique. An efficient room-temperature pulsed and continuous wave (CW) lasing with the CdSe:Cr crystal was achieved. First a pulsed lasing with the CdS:Cr crystal was also demonstrated. The slope efficiency on the absorbed energy was as high as 46.5% for Cr 2+:CdSe and 39% for Cr 2+:CdS lasers. Using an intra-cavity prism, the Cr 2+:CdSe laser wavelength was continuously tuned from 2.26 to 3.61 μm while the Cr 2+:CdS laser from 2.2 to 3.3 μm. For the laser wavelength, the crystal passive loss coefficient was estimated to be smaller than 0.045 cm −1 for CdSe:Cr crystals and 0.039 cm −1 for CdS:Cr crystals. For the Cr 2+:CdSe laser, the CW output power up to 1.07 W was achieved.

Influence of dynamic deformation on the parameters of pulsed semiconductor lasers pumped by an electron beam

The experimental results were explained by regarding the active element of a pulsed electron-beam-pumped semiconductor laser as an acoustic cell. Measurements were made of the divergence of the radiation emitted by a CdS laser pumped by pulses of 250 keV electrons of 1 and 10 ns duration. The watt-ampere characteristics of the output radiation were determined for crystals pumped through a slit aperture oriented along or across the crystallographic c axis. Measurements were made also of the dimensions of the damage zones in transversely pumped lasers when the energy of the pump pulses was varied. The results obtained were explained by the appearance of elastic strains in a crystal during and after the end of a pump pulse.

Limits of validity of models of a homogeneously broadened emission line of a CdS laser

A model of a homogeneously broadened emission line of an electron-beam-pumped semiconductor laser is modified to deal with the case when the population of the radiative level is close to the equilibrium value. This is done in such a way that all the parameters in the modified model can easily be determined experimentally. An analysis is made of the limits of validity of models of an inhomogeneously broadened emission line.

Electron-beam-pumped two-dimensional semiconductor laser array with tilted mirror resonator

The spatial and spectral emission characteristics of a two-dimensional CdS laser array, pumped by a high-energy electron beam, have been experimentally investigated. The near-field emission from each cell or array element is found to arise from a virtual line located behind the cell. The results are consistent with a geometric ray model of a tilted mirror resonator.

Dye lasers pumped by radiation from high-power semiconductor lasers

Dye lasers were pumped for the first time with radiation from high-power CdS and ZnO semiconductor lasers. The latter lasers were pumped by a beam of 350 keV electrons of 150 A/cm2 current density in the form of pulses of 25 nsec duration. Use was made of multicomponent semiconductor targets up to 50 mm in diameter. A special optical system was developed for focusing radiation in a dye cell. The efficiencies of conversion of the pump radiation into the dye laser radiation were 50% for the rhodamine 6G–CdS pair (when the output energy per pulse was 50 mJ) and 10% for the coumarin 47–ZnO pair.

Electron-pumped high-efficiency semiconductor laser

We report on an efficient semiconductor laser array pumped by a high-energy electron gun. A peak power of 350 kW in a 4-ns pulse has been measured from a 25-mm2 CdS laser. For the materials studied (CdS, ZnxCd1−xS, and ZnSxSe1−x), laser action has been obtained in the blue-green region of the spectrum.

Electron beam stimulated nonthermal crystallization of CdS surface layers: Observations by real-time atomic-resolution electron microscopy

The transformations of partially amorphous CdS surfaces induced by 100–400 keV electrons have been followed in real time by atomic-resolution electron microscopy. A definite sequence of atomic rearrangements leading to nucleation and growth of CdS and Cd crystals was observed. These processes are believed to be due to nonthermal mechanisms involving inelastic electron collisions rather than direct knock-on collisions between electrons and the atomic nuclei since there is no threshold over the range of incident electron energies. These effects may be responsible for the degradation of electron beam pumped CdS lasers which has been reported elsewhere.

Characteristics of CdS laser screen radiation at 300 °K

An experimental investigation was made of the dependences of the lasing threshold, power, and spectrum on the thickness of a crystal, reflection coefficients of the resonator mirrors, and rate of scanning with an electron beam. The reasons for catastrophic degradation of laser screens at 300 °K were analyzed. Estimates were obtained of the maximum power and optimum diameter of the electron beam for a CdS laser screen operating as a television raster at 300 °K.

Investigation of degradation of electron-beam-pumped cadmium sulfide lasers

An investigation was made of the degradation effects of the emitted radiation and of 50 keV electron-beam pumping on the emission characteristics of CdS lasers. Catastrophic and gradual degradation processes in CdS crystals were studied. An analysis was made of the mechanism of charging of the impurity centers, which was responsible for the instability of the output power, and of the ''potential displacement'' of sulfur atoms from regular sites in the CdS lattice, which reduced the internal quantum efficiency.

Dependences of Laser Wavelength and Pumping Power at Threshold on Cavity Length in Electron-Beam-Pumped CdS Laser

A shift of a laser line to a longer wavelength is observed with the increase in the cavity length from 20 to 300 µm at 82 and 300 K in an electron-beam-pumped CdS laser. With an increase in the reflectivity of the cavity end, the laser line similarly shifts to longer wavelengths. These shifts of the laser line are shown to be due to reabsorption of the emitted light in the crystal. The dependence of the laser wavelength on the cavity length and the reflectivity is calculated from an approximate gain curve of a Gaussian shape and an absorption curve given by Urbach's rule. The dependence of the threshold current density of the pumping electron beam on the cavity length is also explained by this model.

Use of a cathode-ray tube with a semiconductor laser screen for recording of phase holograms in photoolastic materials

Holograms of plane wave fronts were recorded in photoplastic materials using a cathode-ray tube with a CdS laser screen. The output power of the laser pulses was 1.5 W and their duration was 200 nsec, which was sufficient for the recording of one hologram in a pulse. The light-modulation characteristics of the recorded holograms were determined.

Stimulated Emission of Polaritons

The gain of optically pumped CdS lasers is calculated assuming that stimulated emission occurs with photonlike polaritons created in inelastic exciton-exciton collisions; it is shown that gain constants of the recently observed magnitude can be expected from this mechanism.

Internal Q-Switching in a CdS Laser Pumped by an Electron Beam

Internal Q-Switching in a CdS Laser Pumped by an Electron Beam