Room-temperature Laser Action Research Articles

Plasmon-Assisted Nd(3+)-Based Solid-State Nanolaser.

Solid-state lasers constitute essential tools in a variety of scientific and technological areas, being available in many different designs. However, although nanolasing has been successfully achieved for dyes and semiconductor gain media associated with plasmonic structures, the operation of solid-state lasers beyond the diffraction limit has not been reported yet. Here, we demonstrate room temperature laser action with subwavelength confinement in a Nd(3+)-based solid-state laser by means of the localized surface plasmon resonances supported by chains of metallic nanoparticles. We show a 50% reduction of the pump power at threshold and a remarkable 15-fold improvement of the slope efficiency with respect to the bulk laser operation. The results can be extended to the large diversity of solid-state lasers with the subsequent impact on their applications.

Structural Origin and Laser Performance of Thulium-Doped Germanate Glasses

The structural origin and laser performance of thulium-doped germanate glasses have been studied. The investigation includes two main sections. The first part discusses the Raman spectroscopic and thermal stability of the host glass structure. The low value of the largest phonon energy (850 cm(-1)) reduces the probability of nonradiative relaxation. The large emission cross section of the Tm(3+) : (3)F(4) level (8.69 × 10(-21) cm(2)), the high quantum efficiency of the (3)F(4) level (71%), and the low nonradiative relaxation rate of the (3)F(4) → (3)H(6) transition (0.09 ms(-1)) illustrate good optical properties of the germanate glass. In the second part, the room-temperature laser action from the thulium-doped germanate glass is demonstrated when pumped by a 790 nm laser diode. The maximum output power of 346 mW and slope efficiency of 25.6% are achieved.

Vertical cavity surface emitting laser action of an all monolithic ZnO-based microcavity

We report on room temperature laser action of an all monolithic ZnO-based vertical cavity surface emitting laser (VCSEL) under optical pumping. The VCSEL structure consists of a 2λ microcavity containing eight ZnO/Zn0.92Mg0.08O quantum wells embedded in epitaxially grown Zn0.92Mg0.08O/Zn0.65Mg0.35O distributed Bragg reflectors (DBRs). As a prerequisite, design and growth of high reflectivity DBRs based on ZnO and (Zn,Mg)O for optical devices operating in the ultraviolet and blue-green spectral ranges are discussed.

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.

Judd–Ofelt analysis of spectra and experimental evaluation of laser performance of Tm3+ doped Lu2SiO5 crystal

This paper reports that the Tm3+:Lu2SiO5 (Tm:LSO) crystal is grown by Czochralski technique. The room-temperature absorption spectra of Tm:LSO crystal are measured on a b-cut sample with 4 at.% thulium. According to the obtained Judd–Ofelt intensity parameters Ω2 = 9.3155 × 10−20 cm2, Ω4 = 8.4103 × 10−20 cm2,Ω6 = 1.5908 × 10−20 cm2, the fluorescence lifetime is calculated to be 2.03 ms for 3F4 → 3H6 transition, and the integrated emission cross section is 5.81 × 10−18 cm2. Room-temperature laser action near 2μm under diode pumping is experimentally evaluated in Tm:LSO. An optical-optical conversion efficiency of 9.1% and a slope efficiency of 16.2% are obtained with continuous-wave maximum output power of 0.67 W. The emission wavelengths of Tm:LSO laser are centred around 2.06 μm with spectral bandwidth of ∼13.6 nm.

ZnO lasing in complex systems with tetrapods

A ZnO structure in the form of a core–shell wire was grown with a modified vapour transport and condensation method. The wire consists of a dense core which may play the role of a waveguide and a shell formed mainly from tetrapod-type crystallites. The high optical quality of the produced ZnO material is confirmed by continuous wave photoluminescence (PL) analysis demonstrating that low- temperature PL is related to the recombination of bound excitons, while room-temperature PL is due to free excitons. Good quality of the crystal structure is demonstrated also by the Raman spectrum. The shell of the wire exhibits room-temperature laser action due to lasing modes in tetrapods under the excitation by nanosecond laser pulses. The nature of the lasing modes is discussed. A simplified model for one of the possible modes is suggested.

High quality nitride based microdisks obtained via selective wet etching of AlInN sacrificial layers

The authors report a technique for selective wet chemical etching of an AlInN sacrificial layer lattice-matched to GaN for the fabrication of air-gap photonic structures. It is used to demonstrate high quality factor (Q) microdisk cavities. Whispering gallery modes are observed in the photoluminescence spectra of InGaN∕GaN quantum wells (QWs) embedded in the GaN microdisks. Q factors of up to 3500 are obtained. The measured Qs are found to be limited by the QW absorption. Room temperature laser action is achieved for a wide spectral range (409–475nm) with a threshold down to 166kW∕cm2.

An optoelectronic device in bulk LiF with sub-micron periodic gratings fabricated by interference of 400 nm femtosecond laser pulses

Sub-micron periodic gratings of transparent materials are holographically fabricated by interference with the second harmonic (400nm) of a mode-locked Ti:sapphire oscillator–amplifier laser. As one optoelectronic application, a pulsed, room temperature laser action in bulk lithium fluoride is demonstrated, for the first time, in the green spectral region based on the laser-active F3+ colour centres utilizing a distributed feedback structure encoded by interference of 400nm femtosecond laser pulses. A lasing output with a linewidth of 1nm is obtained at approximately 539nm, which value reflects the selective laser resonator. Realization of green and red distributed feedback colour centre laser action based on the F3+ and F2 centres in LiF excited by a single wavelength can be expected.

Tm-doped LiLuF_4 crystal for efficient laser action in the wavelength range from 182 to 206 μm

Room-temperature continuous-wave laser action in a novel Tm-doped LiLuF(4) crystal emitting at around 1.9 microm is demonstrated. The crystal growth process, spectroscopic measurements, and laser performance are presented for different Tm concentrations. An overall tunability extending from 1817 to 2056 nm, a slope efficiency of 46%, and a maximum output power in excess of 1.1 W are reported.

Room temperature laser action from multiple bands in photoexcited GaN grown on a silicon substrate

Room temperature stimulated emission and laser action with well developed longitudinal optical modes from high-quality GaN films grown on silicon substrates by metal-organic chemical-vapor deposition are presented. Laser action with well developed Fabry-Pérot modes involving the A, B, and C bands was observed. Stimulated emission one exciton below the A band and the B band and one longitudinal optical phonon below the B band was also observed. The effective index of refraction during laser operation was measured to be 2.9.

Formation conditions of random laser cavities in annealed ZnO epilayers

The possibilities to realize room-temperature random laser action in ZnO epilayers with MgO as the buffer layer are studied. It is found that the formation of random laser cavities inside the ZnO epilayers can be achieved by post-growth annealing. Incoherent and coherent random lasing phenomena are observed from ZnO epilayers with (220)- and [200]-oriented MgO buffer layers, respectively. Lasing linewidth of the ZnO epilayers with incoherent and coherent feedback under 355-nm optical excitation is found to be /spl sim/4 and /spl sim/0.4 nm, respectively.

Continuous-wave laser oscillation at 929nm from a Nd3+-doped LiNbO3:ZnO nonlinear laser crystal: A powerful tool for blue laser light generation

This work reports on room-temperature continuous-wave laser action at 929nm from a Nd3+:LiNbO3 nonlinear laser crystal co-doped with ZnO. The spectroscopic parameters of the quasi-three-level F3∕24→I9∕24 laser channel are discussed. In nonoptimal preliminary experiments, pump power at threshold was found to be as low as 105mW.

Realization of quantum cascade laser operating at room temperature

X-ray diffraction, as an effective probe and simple method, is used to ascertain the precise control of the epilayer thickness and composition. Intersubband absorption from the whole structure of the QC laser is used to monitor the wavelength of the QC laser and the material quality. Path for growth of high-quality InP-based InGaAs/InAlAs quantum cascade laser material is realized. The absorption between two quantized energy levels is achieved at ∼4.7 μm. Room temperature laser action is achieved at λ≈5.1–5.2 μm. For some devices, if the peak output power is kept at 2 mW, quasi-continuous wave operation at room temperature can persist for more than 1 h.

Room-temperature Tm, Ho:LuLiF_4 laser with a novel quasi-end-pumping technique

A novel diode-pumped, efficient, quasi-end-pumping scheme that uses two lens ducts to achieve homogeneous pumping in a gain medium was proposed and evaluated. With this technique, room-temperature laser action at a pulse repetition frequency up to 20 Hz was demonstrated in 5%Tm, 0.5%Ho:LuLiF(4), which we grew by the Czochralski method. At 10 Hz a long-pulse laser output energy in excess of 24 mJ and a slope efficiency with respect to the incident pump energy of 10.7% were obtained.

Room Temperature Laser Action in Laterally Overgrown GaN Pyramids on (111) Silicon

Single and multi-mode room temperature laser action was observed in GaN pyramids under strong optical pumping. The 5- and 15-micron-wide hexagonal-based pyramids were laterally overgrown on a patterned GaN/AlN seeding layer grown on a (111) silicon substrate by metal-organic chemical vapor deposition. The pyramids were individually pumped, imaged, and spectrally analyzed through a high magnification optical system using a high density pulsed excitation source. We suggest that the cavity formed in a pyramid is of a ring type, formed by total internal reflections of light off the pyramids’ surfaces. The mode spacing of the laser emission was found to be correlated to the size of pyramids. The effects of pyramid geometry and pulse excitation on the nature of laser oscillations inside of the pyramids is discussed. Practical applications of the results for the development of light-emitting pixels and laser arrays are suggested.

Room Temperature Laser Action in Laterally Overgrown GaN Pyramids on (111) Silicon

AbstractSingle and multi-mode room temperature laser action was observed in GaN pyramids under strong optical pumping. The 5- and 15-micron-wide hexagonal-based pyramids were laterally overgrown on a patterned GaN/AlN seeding layer grown on a (111) silicon substrate by metal-organic chemical vapor deposition. The pyramids were individually pumped, imaged, and spectrally analyzed through a high magnification optical system using a high density pulsed excitation source. We suggest that the cavity formed in a pyramid is of a ring type, formed by total internal reflections of light off the pyramids' surfaces. The mode spacing of the laser emission was found to be correlated to the size of pyramids. The effects of pyramid geometry and pulse excitation on the nature of laser oscillations inside of the pyramids is discussed.

Characterization of a Ho^3+-doped fluoride fiber laser with a 39-μm emission wavelength

The fluoride fiber laser with the longest emission wavelength, the Ho(3+)-transition at 3.9 mum in the attenuation minimum of the 3-5-mum atmospheric window, is characterized. After reviewing the importance of fluoride fibers due to their low phonon energies, we describe room-temperature fluorescence and laser action with liquid-nitrogen cooling. Continuous-wave laser action at 3.9 mum is presented for the 640- and the 890-nm pump ranges. A shift of the emission wavelength is achieved by varying the resonator mirrors. Laser characteristics and temperature dependence are discussed.

Demonstration of room-temperature laser action at 25 µm from Cr^2+:Cd_085Mn_015Te

Room-temperature laser action from Cr(2+)-doped Cd(0.85)Mn(0.15)Te has been demonstrated for what is believed to be the first time. We achieved pulsed laser operation centered at ~2.5mu m by pumping into the mid-infrared absorption band of Cr(2+) ions by use of the 1.907- mum output of a H(2) Raman-shifted Nd:YAG laser. The output of the free-running Cr(2+):Cd(0.85)Mn(0.15)Te laser had a width of ~50 nm (FWHM), and the slope efficiency was calculated to be 5.5% under nonoptimum conditions.

Spectroscopic study and laser operation of Cr 4+-doped (Sr,Ca)Gd 4(SiO 4) 3O single crystals

Cr-doped oxyapatite single crystals with formula AGd 4(SiO 4) 3O and A = Sr or Ca were grown and studied. The shape and the intensity of their optical absorption and fluorescence bands as well as the values and the temperature variations of the fluorescence lifetimes are characteristic of those of tetrahedrally coordinated Cr 4+ ions. Gain measurements show their potential wavelength tunability between about 1.2 and 1.5 μm. Room temperature laser action is demonstrated at 1.37 and 1.44 μm in the Ca- and Sr-compounds, respectively.

Nd:CaYAlO4—a new crystal for solid-state lasers emitting at 1.08 μm

Crystals with the K2 NiF4 structure are good hosts for transition metal and rare-earth ions. Continuous-wave room-temperature laser action in a neodymium-doped crystal with this structure, CaYAlO4 , was observed using a GaAlAs diode laser array for end pumping of the laser rod. The free-running laser operated at a wavelength of 1080.6 nm.