6.2 W laser-diode end-pumped continuous-wave Nd:YALO3 laser at 1.34 μm

We report a compact and efficient LD end-pumped linearly polarized Nd:YAP laser operating at 1.34 μm. The laser system with different crystal lengths, output couplers and cavity types were compared. Based on optimizing of the pump system and laser cavity, 6.2 W laser radiation at 1341.4 nm with c-axis polarized was achieved, corresponding to an optical conversion efficiency of about 24.8% with respect to the incident pump power. The laser threshold was only about 1.3 W and the optical slope efficiency was up to 27.2%.     

26.3-W continuous-wave, diode-double-end-pumped all-solid-state Nd:GdVO4 laser operating at 1.34 μm

A high-power continuous-wave (CW) all-solid-state Nd:GdVO₄ laser operating at 1.34 μm is reported here. The laser consists of a low doped level Nd:GdVO₄ crystal double-end-pumped by two high-power fiber-coupled diode lasers and a simple plane-parallel cavity. At an incident pump power of 88.8 W, a maximum CW output of 26.3 W at 1.34 μm is obtained with a slope efficiency of 33.7%. To the best of our knowledge, this is the highest output at 1.34 μm ever generated by diode-end-pumped all-solid-state lasers.     

Continuous-tunable 4.144-4.851 μm twin-MgO:PPLN cascaded optical parametric generator pumped by a 1.342 μm Nd:GdVO4 laser

An all-solid-state mid-infrared optical parametric generator with wide tunability by using multi-grating periodically poled 5 mol.-% MgO-doped lithium niobate (MgO:PPLN) is reported. The pump source is a diode-pumped Q-switched Nd:GdVO₄ laser operated at 1.342 μm with pulse width of 150 ns and repetition rate of 50 kHz. To extend the interaction length, two identical multi-grating MgO:PPLN crystals have been cascaded in the OPG system. When the incident pump average power is 10 W, the obtained maximum idler output power is 340 mW at 4.144 μm. Compared with only using one multi-grating MgO:PPLN crystal, the obtained idler output power increases by 20.1%. 4.144-4.851 μm continuous-tunable idler output is obtained with six grating periods from 29 to 31.5 μm and temperature from 40 to 200 °C. To our knowledge, this is the first time to use 1.342 μm laser as the pump source of OPG.     

A high-power continuous-wave diffraction-limited Nd:GdVO4 laser operating at 1.34 μm

High-power and high beam quality continuous-wave (CW) Nd:GdVO₄ lasers operating at 1.34 μm were experimentally demonstrated. The lasers consisted of either one or two crystals, which were both end-pumped by high-power fiber-coupled diode lasers. With one crystal, the maximum CW output power generated was 8.4 W. When two crystals were used, a maximum output power of 15.7 W was achieved with the incident pump power of 76.2 W, showing a slope efficiency of 26.2% and an optical-to-optical efficiency of 20.6%. The beam divergence at an output power of 15 W was measured to be about two times that of the diffraction limit.     

Narrow line-width resonant cavity enhanced photodetectors operating at 1.55 μm

A method for fabrication of long-wavelength narrow line-width InGaAs resonant cavity enhanced (RCE) photodetectors in a silicon substrate operating at the wavelength range of 1.3-1.6 μm has been developed. A full width at half maximum (FWHM) of 0.7 nm and a peak responsivity of 0.16 A/W at the resonance wavelength of 1.55 μm have been accomplished by using a thick InP layer as part of the resonant cavity. The effects of roughness and tilt of the InP layer surface, and its free carrier absorption, as well as the thickness deviation of the mirror pair on the resonance wavelength shift and the peak quantum efficiency of the RCE photodetectors are analyzed in detail, and approaches for minimizing them toward superior performance are suggested.     

A 7-W diode-pumped Nd:YVO4 cw laser at 1.34 μm

A Nd:YVO₄ laser, end-pumped by a fiber-coupled diode-laser array, generates 7.3 W of output power at 1342 nm, the highest so far reported for this host crystal. The slope efficiency is 40% and the output-beam divergence is close to the diffraction limit. An important point in attaining such results is the choice of crystals with low Nd concentration. Received: 16 July 2002 / Published online: 25 October 2002 RID="*" ID="*"Corresponding author. Fax: +39-050/844333, E-mail: dilieto@df.unipi.it RID="**" ID="**"Permanent address: Scuola Normale Superiore, Piazza dei Cavalieri 7, Pisa, Italy     

Diode-pumped cw and Q-switched Nd:GdVO4 laser operating at 1.34 μm

A diode-pumped 1.34 m Nd:GdVO₄ laser operating in cw and active Q-switching modes has been demonstrated. 4.15 W of cw output power was obtained at the highest attainable pump power of 12.3 W, resulting in an optical conversion efficiency of 33.7%, the slope efficiency was determined to be 37.6%. In Q-switching operation, a maximum average output power of 2.7 W was generated at pulse repetition frequency (PRF) of 50 kHz, with an optical conversion efficiency of 22% and a slope efficiency of 29.2%. The laser pulses with shortest duration, highest energy and peak power were achieved at PRF of 10 kHz, the parameters being 15 ns, 160 J, and 10.7 kW, respectively. By intracavity frequency-doubling with a type II phased-matched KTP crystal, 0.62 W average power at 0.67 m was produced at a PRF of 15 kHz, the resulting pulse energy, peak power, and pulse width being 41.3 J, 2.2 kW, and 19 ns, respectively. A group of analytical formulae, based on rate equations, are presented to evaluate the operational parameters of an actively Q-switched laser. Calculated results were found to be in close consistency with the experimental data.     

Investigation on achieving the diode-pumped weak line laser at 1.3 μm

In this paper, a continuous-wave (CW) diode-side-pumped Nd:YAlO₃ (Nd:YAP) laser operating at the weak line of 1339 nm has been achieved and investigated. The output of the 1339 nm laser was realized based on the polarization selection and reasonable transmittance design. The relationship between the output powers and resonator lengths of the 1339 nm Nd:YAP laser has been studied and the optimum resonator length was adopted to improve the output power. As high as 31.3 W output power of the a-axis polarized 1339 nm laser has been obtained at the pumping power of 555 W with the optical-optical and slope efficiencies to be 5.6% and 13%, respectively. This work will provide an effective way to obtain the weak line lasers for potential applications in spectroscopy, coherent terahertz generation, etc.     

A 13.3-W laser-diode-array end-pumped Nd:GdVO4 continuous-wave laser at 1.34 μm

We report a high-power laser-diode-array end-pumped 0.3 at.% Nd:GdVO₄ continuous-wave laser operating at 1.34 m. The maximum output power of 13.3 W was obtained at the incident pump power of 49.2 W, giving the corresponding optical conversion efficiency of 27% and the average slope efficiency of 28.5%. The thermal focal length of the Nd:GdVO₄ crystal under the pump power from 15.3 to 50 W was measured experimentally. PACS 42.55.Xi; 42.70.Hj     

Diode-pumped doubly passively Q-switched c-cut Nd:GdVO4 1.34 μm laser with V:YAG and Co:LMA saturable absorbers

By simultaneously using both V³⁺:YAG and Co:LMA saturable absorbers in the cavity, a diode-pumped doubly passively Q-switched c-cut Nd:GdVO₄ laser at 1.34 μm is demonstrated for the first time. The average output power, the pulse width and the pulse repetition rate have been measured. The experimental results show that the doubly passively Q-switched laser can generate shorter pulse width with higher peak power in comparison to the singly passively Q-switched laser only with V³⁺:YAG or Co:LMA saturable absorber. At the pump power 13 W, the pulse width has been compressed 83% and the peak power has been improved 15 times, respectively.     

Temperature-dependent absorptance of painted aluminum, stainless steel 304, and titanium for 1.07 μm and 10.6 μm laser beams

We measured the temperature-dependent absorptance of metals (Al, Ti, SS304) for continuous beams from 1.07 μm fiber laser and 10.6 μm CO₂ laser using power sensors and infrared (IR) pyrometers. The absorptance measurements were repeated for metals with three different paint coatings. For measurements at elevated temperatures up to the melting point, integrating sphere is not practical since high temperature radiation from a heated target disturbs weak output from the sphere considerably. Our results provide how each metal, whether coated or uncoated, absorbs the infrared beams as temperature is elevated to a melting point. A polynomial approximation to the measured absorptance of each target is provided for modeling of the laser-metal interaction at elevated temperatures.     

Amplification characteristics measurement of 1.55 μm multi-mode LD

The amplification characteristics of 1.55 μm multi-mode LD are presented experimentally. It demonstrates that nine wavelengths across 1547–1557 nm have a good amplification, the maximum gain of ∼43 dB at 1552.14 nm is obtained with pump power of 130 mW @980 nm, and noise figure of ∼5.6 dB at 1554.3 nm is achieved.     

Graphene-based passively Q-switched 2 μm thulium-doped fiber laser

We demonstrated stable pulses generation at 2 μm in a passively Q-switched thulium-doped fiber laser using a few layer graphene thin film. The maximum output power was 4.5 mW and the single pulse energy was 85 nJ at 53 kHz repetition rate, and the pulse width was about 1.4 μs. The pulse width and the repetition rate of the Q-switched fiber laser can be changed along with the pump power. To the best of our knowledge, this is the first report of graphene saturable absorber for passively Q-switched 2 μm fiber lasers.     

Thermal simulation of InP-based 1.3 μm vertical cavity surface emitting laser with AsSb-based DBRs

In this paper, the thermal analysis of double-intracavity tunnel-junction vertical cavity surface emitting laser is theoretically performed using simulation software PICS3D which self-consistently combines 3D simulation of carrier transport, self-heating and optical wave-guiding. Excellent agreement between simulation and measurement is obtained by careful adjustment of material parameter in model. The temperature distribution of the device is obtained at 20 °C and 6o °C stage temperature. Quantum well maximum temperature for operating device is in very good agreement with experimental results.Simulation results show that Joule heating is the main heat source in device. Vertical electron escape into Separate Confinement Heterostructure causes thermal power roll-off. Self-heating and optical reductions are the triggering mechanisms behind the leakage current. Laser design variations are shown to allow a significant increase in the maximum output power. This optimized structure can also enhance the stimulated recombination rate and decrease the Auger recombination rate.     

High-power 1.5 and 3.4 μm intracavity KTA OPO driven by a diode-pumped Q-switched Nd:YAG laser

With a non-critically phase-matched KTA crystal, a high-power intracavity optical parametric oscillator (IOPO) driven by a diode-side-pumped acousto-optically Q-switched Nd:YAG laser has been realized. The maximum average output power of 13.6 W at the signal wavelength of 1534 nm and 3 W at the idler wavelength of 3472.7 nm were obtained with the repetition rate of 18 kHz, giving the optical-optical conversion efficiency of about 5.7% from diode-power at 808 nm to OPO signal output, which was the highest conversion efficiency for intracavity KTA OPO with diode-side-pumping configurations to our best knowledge. At the highest output power of 13.6 W, the signal pulse duration of 5.46 ns was obtained, corresponding to the single pulse energy of 756 μJ and peak power of 138 kW, respectively.     

1.34 μm fluorescence and laser properties of Nd:La0.11Y0.89VO4 crystal

For Nd:La_xY_1−xVO₄ (x = 0.11) crystal, the ⁴F_3/2 → ⁴I_13/2 transition property was investigated for the first time. The fluorescence peak of Nd:La_0.11Y_0.89VO₄ crystal exhibited obvious inhomogeneous broadening comparing with that of Nd:YVO₄ crystal. With laser diode array as pump source, 1.34 μm continuous-wave (CW) and active Q-switched laser operations based on ⁴F_3/2 → ⁴I_13/2 transition were realized. For CW laser operation, the maximum output power of 2.47, 2.13 W is obtained with slope efficiencies of 29.4%, 27.6%, and optical to optical conversion efficiency of 26.2%, 24.7%, respectively for a, c cut crystal samples. For acousto-optic (AO) Q-switched laser operation, the shortest pulse width, highest peak power and maximum pulse energy came from the a-cut sample, which were 13 ns, 2.69 kW and 35 μJ, respectively.     

Passively mode locked femtosecond Tm:Sc2O3 laser at 2.1 μm

We report on the passive mode locking of a Tm3+:Sc2O3 laser at 2.1 μm using a semiconductor saturable absorber mirror based on InGaAsSb quantum wells. Transform-limited 218 fs pulses are generated with an average power of 210 mW. A maximum output power of 325 mW is produced during mode locking with the corresponding pulse duration of 246 fs at a pulse repetition frequency of 124.3 MHz. A Ti:sapphire laser is used as the pump source operating at 796 nm.     

LD pumped 2-μm CW laser from Tm,Ho:GdVO_4

A set of fiber-coupled continuous wave (CW) diode lasers has been used to pump Tm, Ho:GdVO_4 and generate 2.048-μm laser radiation at liquid nitrogen temperature. The optical-optical efficiencies of 25%, output power of 3.5 W, and pumping threshold of 838 mW have been obtained and compared with those from Tm, Ho:YLF under identical experimental conditions.     

6.5-ns actively Q-switched Nd:YVO_4 laser operating at 1.34 μm

With a plano-concave cavity,diode-pumped continuous-wave(CW) and actively Q-switched Nd:YVO4 laser operating at 1.34 μm is demonstrated.Maximum CW output power of 4.76 W and Q-switched average output power of 2.64 W are obtained with output coupler(transmission T = 3.9%).For the Q-switching operation,the theoretically calculated pulse energy and pulse width,with a pulse repetition frequency(PRF) range of 5-40 kHz,coincide with the experimental results.With a T = 11.9% output coupler,the maximum peak power of 24.3 kW and minimum pulse width of 6.5 ns are obtained when the PRF is 10 kHz.To the best of our knowledge,this is the shortest actively Q-switched pulse duration ever obtained in a 1.3-μm Nd-doped vanadate laser.