YAlO3 Laser Research Articles

Diode-pumped, continuous-wave Tm:YAIO_3 laser

A continuous-wave, diode-pumped, room-temperature Tm:YAlO3 laser was built, characterized, and compared with a theoretical model. Spectroscopic parameters of the laser crystal, such as the pump band ((3)H4 manifold) lifetime, the upper laser level ((3)F4 manifold) lifetime, and the absorption coefficient were measured. The experimental data were used to calculate the quantum efficiency of Tm self-quenching of the (3)H4 manifold.

Holmium lasers passively Q-switched with PbS quantum-dot-doped glasses

PbS quantum-dot-doped glasses are demonstrated as saturable absorber Q-switches for 2 microm holmium lasers. Q-switched pulses from Ho3+:Y3Sc2Al3O12 and Ho3+:Y3Al5O12 lasers of 50 and 70 ns in duration, respectively, have been obtained demonstrating up to 13% of energy conversion efficiency from free-running to Q-switched output.

Diode-pumped cw Tm3+:YAlO3 laser

The output parameters of a Tm3+:YAlO3 laser pumped by laser diodes in the spectral region 802–810 nm are studied. The output cw power exceeded 10 W for the total efficiency above 30%. The laser wavelength varies in the range from 1946 to 1985 nm and is determined by the pump power and resonator losses in this spectral region. The efficiency of cross relaxation process during the population of the 3F4 laser level is measured.

Absorption intensities and emission cross sections of principal intermanifold and inter-Stark transitions of Er3+(4f11) in polycrystalline ceramic garnet Y3Al5O12

A comparative spectroscopic study is performed on Er3+(4f11) ions doped in polycrystalline ceramic garnet Y3Al5O12 (YAG) and single-crystal laser rod, both containing nominal 50 at. % of Er3+. The standard Judd–Ofelt (JO) model is applied to the room-temperature absorption intensities of Er3+(4f11) transitions in both hosts to obtain the phenomenological intensity parameters. These parameters are subsequently used to determine the radiative decay rates, radiative lifetimes, and branching ratios of the Er3+ transitions from the upper multiplet manifolds to the corresponding lower-lying multiplet manifolds LJ2S+1 of Er3+(4f11) in these garnet hosts. The emission cross sections of the intermanifold Er3+I13∕24→I15∕24 (1.5 μm) transition as well as the principal inter-Stark transition Y1→Z4 (1550 nm) within the corresponding multiplet manifolds have been determined. The room-temperature fluorescence lifetimes of the I13∕24→I15∕24 (1.5 μm) transition in both polycrystalline ceramic and single-crystal YAG samples were measured. From the radiative lifetimes determined from the JO model and the measured fluorescence lifetimes, the quantum efficiencies for both samples were determined. The comparative study of Er3+(4f11) ions performed suggests that polycrystalline ceramic YAG is an excellent alternative to single-crystal YAG rod for certain applications.

Upconversion dynamics in Pr-doped YAlO3 and Y3Al5O12 laser crystals

The praseodymium ion in solids exhibits emission from a number of levels located in different regions of the spectrum and presents various spectral features that include anti-Stokes emission, otherwise called upconversion. We have examined this phenomenon in two laser crystals YAlO3 and Y3Al5O12 doped with praseodymium. We studied the dynamics of the upconversion of the exciting energy by measuring decay patterns and emission intensities as function of excitation and temperature in the range 24–300 K. The experimental data indicate that the mechanisms responsible for the upconverted emission are energy transfer in YAlO3 and excited state absorption in Y3Al5O12. The mechanism of upconversion for each system persists at all temperatures. We observed upconverted emission in both samples when exciting the system in the 1D2 level with light from a dye laser at ∼599 nm. In YAlO3:Pr this emission is due to transitions originating in 3P0, a level more energetic than the 1D2 level. We found the intensity of this emission to be proportional to the square of the intensity of the excitation energy. In Y3Al5O12:Pr we observed upconverted emissions originating in the 3P0 level and in the (4f5d) band. We found the former emission to be proportional to the square of the excitation energy, and the latter to the cube of this energy.

Spectral analysis and energy-level structure of Er3+(4f11) in polycrystalline ceramic garnet Y3Al5O12

Absorption spectra obtained between 1550 and 440nm and fluorescence spectra obtained between 1700 and 1500nm are reported in a comparative spectroscopic study of polycrystalline ceramic Y3Al5O12 (YAG) and single-crystal laser rod YAG, both containing 50at.% Er3+ as a dopant in the garnet host. The spectra are observed in both samples at temperatures between 8K and room temperature. The detailed splitting of individual multiplet manifolds, LJ2S+1, Er3+(4f11), by the crystalline electric field is similar in both the ceramic sample and the single-crystal laser rod. With few exceptions, there is little shift in energy (few wave numbers) of individual Stark levels within a manifold, between dilute and concentrated Er3+ samples. This is not too surprising since Y3Al5O12 and Er3Al5O12 form a solid solution with the majority of Er3+ ions occupying cation sites having D2 symmetry in the garnet lattice over the entire solid solution range. As a check on the observed manifold splittings of Er3+ in ceramic YAG, we compared the present results to the calculated splitting that several of us reported earlier for Er3+ in single-crystal YAG. To within the standard deviation reported earlier, the present results agree with that calculation. Thus, one set of atomic and crystal-field parameters describes the splitting of the Er3+ energy levels in either the ceramic or single-crystal host for Er3+ in D2 sites.

Actively stabilised diode pumped Tm:YAlO laser

An actively stabilised, continuous-wave, 1.94 µm Tm:YAlO laser is presented. Optoelectronic negative feedback stabilisation is utilised to prevent relaxation-oscillation-driven spiking. The amplitude stability of the laser is found to be very robust against cavity perturbation and parasitic radiation back-reflection, making it attractive for practical applications.

110 W ceramic Nd3+ : Y3Al5O12 laser

A high-power, continuous-wave 0.6% Nd3+-doped ceramic Y3Al5O12 (Nd:YAG) laser has been developed. 110 W laser output at 1064 nm was obtained, with a slope efficiency of about 41%. The M2 factor was found to be around 6. The laser performance of the ceramic laser material was found to compare favorably with that obtained with single crystal Nd:YAG.

Spray diagnostics using an all-solid-state Nd:YAlO3 laser and fluorescence tracers in commercial gasoline and diesel fuels

A new diode-pumped Nd:YAlO3 laser system emitting pulse bursts at 671 nm has made it possible to apply tracer-laser-induced-fluorescence (LIF) techniques for spray diagnostics not only by using model fuels but in real diesel or gasoline fuel sprays. In this work we characterize possible candidates for LIF tracers that can be excited in the wavelength region of 650–680 nm where commercial diesel fuel is transparent. Two fluorescent dyes, Rhodamine 800 and Atto 680, were identified as possible tracers and tested for their relative fluorescence quantum yield and absorption cross section in a diesel fuel environment as well as their behavior at different temperatures. First results of laser-dropsizing experiments with Rhodamine 800 as a fluorescence tracer are presented.

Relaxation of Bleaching in Lead Sulfide Nanoparticles at Different Pump Powers

Relaxation of bleaching in PbS nanoparticles (of mean size 5.5 nm) has been investigated at different intensities of exciting radiation. The relaxation of bleaching is double exponential with fast (tens of picoseconds) and slow (nanoseconds) components. An increase in the excitation intensity leads to a decrease in the duration of the fast component and an increase in the ratio between the amplitudes of the slow and fast relaxation components. The observed dependences are explained with the aid of the proposed spectroscopic model. A passive mode locking of an Nd:YAlO3 laser emitting at 1.34 μm has been implemented on silicate glass doped with the PbS nanoparticles under study. Pulses of duration 200 psec and energy 0.2 mJ have been obtained.

90 W continuous-wave diode edge-pumped microchip composite Yb:Y3Al5O12 laser

High-power continuous-wave (cw) operation of a diode edge-pumped microchip composite Yb:Y3Al5O12 (YAG) laser is reported. Up to 90 W were obtained from a 400-μm-thick Yb:YAG/YAG structure with a 10 at. % Yb:YAG square core of 2×2 mm2 area; the slope efficiency and optical-to-optical efficiency with respect to the pump power were 40% and 28%, respectively. Measurements of the optical phase distortions induced by pumping gives a focus shift bellow 0.05 m and shows the absence of astigmatic effects, indicating the axial heat flow in this pumping configuration.

High-power blue generation from a periodically poled MgO:LiNbO3 ridge-type waveguide by frequency doubling of a diode end-pumped Nd:Y3Al5O12 laser

Continuous-wave power of 189 mW at 473 nm with 49% conversion efficiency is generated from a 8.5 mm long uncoated periodically polled MgO:LiNbO3 ridge-type waveguide by frequency doubling of a diode end-pumped Nd:Y3Al5O12 laser at room temperature; the corresponding internal blue power and conversion efficiency were 222 mW and 58%, respectively. The highest conversion efficiency of 63% (74% with respect to the blue internal power) was obtained from a 12 mm long waveguide with 99 mW blue output power. Saturation of output blue power was observed for coupled fundamental power into the waveguides in excess of 200 mW.

Basic enhancement of the overall optical efficiency of intracavity frequency-doubling devices for the 1 μm continuous-wave Nd:Y3Al5O12 laser emission

The possibility of basic enhancement of the overall optical-to-optical efficiency of intracavity frequency-doubling devices for the 1 μm continuous-wave (cw) Nd lasers by direct pumping into the emitting level and by using concentrated laser materials is discussed. This possibility is demonstrated for 1.0 and 2.4 at. % Nd:Y3Al5O12 (Nd:YAG) crystals pumped by a Ti:sapphire laser at 885 nm. A slope efficiency of 0.79 in absorbed pump power was obtained for the 1064 nm emission of a 1.0 at. % Nd:YAG crystal. The effect of enhancement of intracavity emission on the second-harmonic emission is manifested in a drastic reduction of emission threshold and in an increased dependence on the absorbed power. The use of concentrated Nd:YAG crystal enables a better use of the pump power and improves the overall optical efficiency of the intracavity frequency-doubling devices.

A hybrid laser system consisting of a frequency-doubled, narrow-line-width, distributed-feedback dye laser oscillator and a high saturation-fluence Ce:LiCaAlF6 crystal amplifier

A tunable narrow-band picosecond dye laser emitting in the ultraviolet region was amplified using a Ce:LiCaAlF6 crystal pumped by the fourth-harmonic emission of a Nd:Y3Al5O12 laser. The single-pass gain obtained exceeded 2 in the spectral range of 288 to 297 nm.

On the analysis of factors limiting third harmonic generation of Nd:YAlO3 laser radiation in barium vapor

The efficiency of generation of the third harmonic (THG) of Nd:YAlO3 laser radiation in barium vapor is analyzed. The influence of the following factors is taken into consideration: the interference of transformed radiation in the case of THG via two channels ω+ω+ω→3ω and 2ω+2ω−ω →3ω, the Kerr effect, two-photon absorption, and the relationship between the energies of the first and second harmonics of radiation. It is shown that the Kerr effect, on the one hand, violates the phase matching conditions in the direct channel but, on the other hand, increases the conversion efficiency due to a defocusing action of the medium, which reduces the influence of the phase detuning between the pumping waves on the process of harmonic generation in the case of generation of difference frequencies. At the same time, the two-photon absorption leads to the depletion of one of the interacting waves (in this case, the second harmonic) and to the prevalence of third harmonic generation through the direct channel.

Cavity configuration for a Q-switched simultaneous dual-wavelength Nd:YAlO_3 laser with the characteristic of polarization-dependent emission cross section

By investigating the rate equations of Q-switched simultaneous dual-wavelength lasers and by using the polarization-dependent emission cross section of a Nd:YAlO3 laser crystal to balance the equivalent emission cross sections of the dual lasing wavelengths, we have developed a new resonator configuration by introducing a quarter-wave polarization rotator. The two wavelengths exhibit an equal net gain in the laser rod, and the optimal spatial and temporal overlap can be achieved easily for optimal sum-frequency mixing. This configuration has a cavity length that is shorter than in previously used configurations, so it is suitable for operation at high output power and with a high repetition rate with a short thermally determined focal length.

Low-loss 13-µm GaInNAs saturable Bragg reflector for high-power picosecond neodymium lasers

A novel low-loss, single-step-growth 1.3-microm GaInNAs saturable Bragg reflector mode-locking element has been developed. Combined radial thickness and postgrowth annealing control have permitted a tuning range of 46 nm for passive mode locking to be demonstrated from one wafer. With this structure, stabilized mode locking was obtained from quasi-cw diode-pumped Nd:YLF and Nd:YALO lasers operating at 1314 and 1342 nm, respectively, with average on-time output powers of as much as 20 W and pulse durations as low as 22 ps.

A simple, high power, compact, intracavity frequency-doubled, Q-switched Nd:Y3Al5O12 laser

We have developed a simple, compact, high power, diode-pumped, intracavity frequency-doubled, Nd:Y3Al5O12 laser capable of generating output powers of up to 70 W at 10 kHz, and 16.5 W at 1 kHz. The output beam quality is highly multimode, with an M2∼30. This, combined with the short output pulse duration of 36–60 ns, and the high average power, makes this laser ideal for pumping ultrafast Ti:sapphire laser amplifier systems.

Intrinsic reduction of the depolarization loss in solid-state lasers by use of a (110)-cut Y3Al5O12 crystal

The depolarization caused by thermally induced birefringence in Y3Al5O12 lasers is intrinsically reduced without any compensation by use of rods cut in other directions than (111). Using a (110)-cut crystal, one can expect the depolarization to become less than 1/10 of that caused in a conventional (111)-cut crystal.

Glass doped with PbS quantum dots as a saturable absorber for 1-μm neodymium lasers

Saturable-absorber mode locking and Q switching of neodymium-doped lasers at 1.06 µm with a PbS-doped glass were demonstrated. Q-switched pulses of 0.3 µJ in energy and 15 ns in duration from a cw diode-pumped Nd3+:KGd(WO4)2 laser and ultrashort pulses of 18 µJ in energy and 70 ps in duration from a Nd3+:Y3Al5O12 laser were obtained. The saturation intensity of the PbS-doped glass (with an average semiconductor crystallite radius of 1.7 nm) was estimated to be 2.3 MW/cm2 at 1.06 µm. The bleaching relaxation time was measured to be 23 ps.