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We have studied and optimized conditions for spontaneous flux growth of RMgB5O10 (R = Y, La, Gd) crystals and assessed the feasibility of seeded growth of such crystals. Using high-temperature solution growth with K2Mo3O10 as a solvent, we have prepared optical-quality (Er,Yb):YMgB5O10 single crystals and measured their thermal conductivity and optical characteristics to assess their potential for use in diode-pumped lasers operating in the spectral range 1.5–1.6 μm. Absorption cross section spectra of an (Er,Yb):YMgB5O10 single crystal have been measured in the spectral ranges 800–1100 and 1400–1650 nm. The results demonstrate that (Er,Yb):YMgB5O10 single crystals are similar in characteristics to (Er,Yb):YAl3(BO3)4, promising for use in advanced near-IR laser systems, and are capable of replacing RAl3(BO3)4 materials in such devices because they are simpler to grow.

Lasing and spectroscopic properties of an LiY0.3Lu0.7F4:Pr3+ crystal grown by the Bridgman–Stockbarger method were investigated in detail. Absorption and luminescence spectra were recorded using polarized light. Lifetimes of excited states 3PJ were determined. Absorption and emission transition intensities were calculated according to f–f-transition intensity theory taking into account interconfiguration interaction. Stimulated emission transverse cross sections were determined using the Fuchtbauer–Ladenburg method. Pumping by an InGaN laser diode produced continuous-wave laser generation at 522.6 nm (3P1 → 3H5) in Pr-doped mixed fluoride crystals with a maximum output power of 0.38 W and a slope efficiency of 19%.

The search for new crystalline host materials for the usage in lasers emitting in the eye-safe spectral range of 1.5–1.6 µm is an important task. The aim of this work was to study the growth technique, spectroscopic properties and laser characteristics of new active media – crystals Er3+,Yb3+:Ca2RE2(BO3)4(RE=Y, Gd).Calcium-yttrium Er3+,Yb3+:Ca3Y2(BO3)4(CYB) and calcium-gadolinium Er3+,Yb3+: Ca2Gd2(BO3)4 (CGB) oxoborate crystals co-doped with erbium and ytterbium ions were investigated. Polarized absorption and emission cross-section spectra were determined. The lifetimes of4I11/2and4I13/2energy levels of Er3+ions were measured and ytterbium-erbium energy transfer efficiencies were estimated. The calculation of the gain cross-section spectra was performed. By using of Er3+,Yb3+: Ca2RE2(BO3)4 (RE=Y, Gd) crystals the laser performance was realized, for the first time to the best of our knowledge. The laser characteristics were studied in a quasi-CW (QCW) laser operation.The wide band with a peak at the wavelength of 976 nm is observed in the absorption spectra of both crystals. This peak coincides with the emission wavelength of the pump laser diodes for Yb-doped active media. The maximum value of absorption cross-section was 1.7 × 10–20cm2for polarizationE//bfor both crystals. The lifetimes of the upper laser level4I13/2of Er3+ions were 580 ± 30 μs and 550 ± 30 μs for Er,Yb:CYB and Er,Yb:CGB crystals, respectively. The energy transfer efficiencies from ytterbium to erbium ions for an Er,Yb:CYB and Er,Yb:CGB crystals were 94 % and 96 %, respectively. According to gain spectrum of the Er,Yb:CYB crystal the gain band peak is centered at the wavelength of 1530 nm. The maximum QCW output power was 0.5 W with slope efficiency of 13 % regarding to absorbed pump power for an Er,Yb: CYB crystal. The laser beam parameter M2did not exceed < 1.5.Based on the obtained results, it can be concluded that these crystals are promising active media for lasers emitting in the spectral range of 1.5–1.6 μm for the usage in laser rangefinder and laser-induced breakdown spectroscopy systems, and LIDARs.

We report on growth, spectroscopy and continuous-wave, mode-locking lasing and chirped pulse regenerative amplification of Yb:YAl3(BO3)4 (Yb:YAB) crystal. Efficient CW laser operation with 9.2 W output power, 46% optical-to-optical and 74% slope efficiencies was demonstrated. Efficient SESAM mode-locked Yb:YAB bulk laser was demonstrated for σ-polarization with 4 W average output power at 70 MHz pulse repetition frequency (PRF) and 195-fs pulse duration resulting in the pulse energy of 57 nJ and pulse peak power of 0.3 MW. Optical-to-optical efficiency of 27% in mode-locked regime is demonstrated. Chirped pulse regenerative amplifier based on Yb:YAB crystal demonstrated with maximum output power of 4.6 W (6 W of chirped pulses and optical-to-optical efficiency of 25%) and 695 fs pulse duration at 100 kHz PRF for the first time to the best of our knowledge.

A series of the new fluoride glasses with small additives of the phosphates doped with different of Nd3+ content is developed. The dopant concentration dependence of optical absorption and emission properties is reported here for the concentration range of 2.5×1020 to 1.0×1021 (ions/cm3). Using the Judd-Ofelt theory the phenomenological intensity parameters Ωt (t = 2; 4; 6) were obtained for all glasses studied. Fluorescence lifetime, quantum efficiency and nonlinear refractive index n2. were obtained. The peak stimulated emission cross sections of the transitions at 899 nm, 1053 nm and 1320 nm were calculated according to J-O theory. The stimulated emission cross-sections of 4F3/2→4I9/2, 4F3/2→4I11/2 and 4F3/2→4I13/2 transitions were determined by the Fuchtbauer-Landenburg equation (FL) and the modified reciprocity method (MR) for all Nd3+concentrations. The analysis of the luminescence quenching depending on the concentration of the activator was carried out. It was concluded that present fluoride glass with small additives of phosphates is a promising material for laser applications.

Diode-pumped femtosecond chirped pulse regenerative amplifiers based on Yb3+-materials are of practical importance for wide range of scientific, industrial and biomedical applications. The aim of this work was to study the amplification of broadband chirped femtosecond pulses in regenerative amplifier based on Yb3+:CaYAlO4crystal.Such systems use femtosecond mode-locked lasers as seed pulse sources and amplify nJ-seed pulses to sub-mJ energy range. Most chirped pulse regenerative amplifier systems described in the literature use seed lasers with typical pulse spectral width at the level of 10–15 nm full width at half maximum (FWHM) that limit the seed pulse duration of about 90 fs and amplified pulse duration at the level of 200 fs due to strong influence of gain narrowing effect on the amplified pulse parameters. Yb3+-doped crystals with wide and smooth gain bandwidth as an active medium of chirped femtosecond pulse regenerative amplification systems allow to reduce negative contribution of gain narrowing effect and lead to shortening of amplified pulses. In this research we study the chirped pulse regenerative amplification of broad-band femtosecond pulses (60 nm spectral width FWHM) in the Yb3+:CaYAlO -based chirped pulse regenerative amplifier. Substantial reduction of the amplified pulse duration down to 120 fs (19.4 nm spectral width FWHM) with average power of 3 W at 200 kHz pulse repetition frequency was demonstrated without any gain narrowing compensation technique.The results of experimental investigation of broad-band seeded Yb3+:CaYAlO -based chirped pulse regenerative amplifier are reported for the first time to our knowledge. 120 fs-pulses (19.4 nm FWHM) with average output power of 3 W were demonstrated without any gain narrowing compensation technique. Despite the significant reduction of amplified pulse duration the task of improvement group velocity dispersion balance (including high orders of group velocity dispersion) remains relevant.

We have studied phase relations in the pseudoquaternary system LuAl3(BO3)4–(K2Mo3O10–Al2O3–B2O3) in the temperature range 1130 to 900°C. The phase relations were represented in graphical form, as a projection of the formation of solid phases in this range onto the composition triangle at 900°C. Optimal results in terms of high-temperature solution growth have been obtained at 25 wt % LuAl3(BO3)4 in the growth charge. Undoped and erbium–ytterbium codoped LuAl3(BO3)4 (LuAB) single crystals have been grown from high-temperature solutions on “pointlike” seeds. The (Er,Yb):LuAB crystals are similar in thermal properties and luminescence spectra to (Er,Yb):YAl3(BO3)4 and (Er,Yb):GdAl3(BO3)4 crystals and can be used in diode-pumped lasers operating in the nominally eye-safe spectral region 1.5–1.6 μm.

In this work we report the spectroscopic properties of Tm3+:NaBi(MoO4)2 crystals with the dopant concentrations of 0.7 at.% and 3 at.%. The energy levels of the Tm3+ in the NaBi(MoO4)2 host were determined from polarized optical absorption and photoluminescence spectra measured at 77.4 K. Radiative properties of the crystals were calculated in context of Judd-Ofelt theory. Raman spectra of the crystal were studied. The concentration dependences of emission decay times of 3H4 and 3F4 levels were analyzed. The potential of the crystal for building tunable and ultrafast pulse lasers is shown on the base of cross sections and gain coefficient in the range of 1.9 μm.

A Sm3+:KY(WO4)2 crystal was grown by the modified Czochralski technique. Polarized absorption and fluorescence spectra, as well as a fluorescence decay curve, were recorded at room temperature. Radiative properties such as emission probabilities, branching ratios and radiative lifetimes were investigated within the framework of the Judd-Ofelt theory as well as the theory of f-f transition intensities which takes into account the influence of the excited configurations. Emission cross section spectra were determined. 4G5/2 fluorescence decay was analyzed within the framework of the Inokuti-Hirayama model. The spectroscopic properties of Sm:KYW crystal were compared with those of other Sm3+-doped materials.

The oxyfluoride-lead-silicate-germanate glass with composition of 30SiO2–10GeO2–xPbO–(50-x)PbF2–10CdF2–yTm2O3, x = 5, 25, 45, y = 0.01, 0.1, 0.5, 1.0 (mol. %) were prepared by melt-quenching technique and their spectroscopic properties, including parameters calculated by the JO method, were studied. A new approach for calculation of the pump efficiency of the 3F4 level at excitation of the 3H4 level by using stationary spectra of luminescence at transitions 3H4→3F4 and 3F4→3H6 was proposed. For the samples with a high content of Tm2O3, the efficiency reaches the value of 1.8. It was established that the quadrupole-quadrupole interaction between thulium ions dominates in the D-A energy transfer due to the cross-relaxation 3H4+3H6→3F4+3F4. On the base of the rate equations, a new fitting procedure was proposed for obtaining the probabilities of donor-acceptor, WDA, and up-conversion, WUP, energy transfer. It was obtained that WDA ~6 105 1/s and WUP « WDA for the samples with 0.5 and 1.0 mol. % of Tm2O3. The laser related properties, the stimulated emission cross-sections, gain spectra, of the glass studied, were obtained and discussed.

Ca9Nd(VO4)7 single crystal was grown by the Czochralski method in inert atmosphere. The crystal structure and chemical composition were studied. Polarized absorption and luminescence spectra were investigated in details. It was found that the Ca9Nd(VO4)7 crystals belongs to self-activated laser materials with a weak concentration quenching of luminescence. Judd-Ofelt analysis was performed. The emission cross-sections spectra for 4F3/2 → 4I9/2, 4I11/2, 4I13/2 transitions were determined. For the first time Raman spectra of the Ca9Nd(VO4)7 single crystal were recorded and interpreted.

Pure and Nd-doped Ca 10 Li(VO 4 ) 7 single crystals were grown by the Czochralski method. The structure of Ca 10 Li(VO 4 ) 7 single crystal was refined starting from a model of Ca 10 K(VO 4 ) 7 using the powder diffraction data collected at a laboratory high-resolution diffractometer. The defect structure of the single crystal was studied with the use of both, high-resolution diffraction using a laboratory instrument and X-ray topographic techniques employing synchrotron radiation at the Hasylab laboratory (Hamburg). Polarized absorption and luminescence spectra of Nd-doped Ca 10 Li(VO 4 ) 7 crystal were investigated in details. The laser oscillation was obtained under flash lamp pumping and the slope efficiency of 0.87% was achieved in the free-running mode. Preliminary examination of lasing properties points that Ca 10 Li(VO 4 ) 7 :Nd crystal can be a highly efficient solid state laser medium. Crystals of this kind are expected to be suitable for application as efficient non-linear optics materials.

We report on growth and detailed spectroscopic study of Eu3+-doped tetragonal sodium gadolinium double tungstate, Eu:NaGd(WO4)2, a new promising crystal for deep-red lasers. Large-volume crystal doped with 4.9 at.% Eu is grown by Czochralski method along the [001] crystallographic direction. Absorption of Eu3+ ions is studied at room temperature (RT) and at 6 K. For the absorption band related to the 7F1 → 5D1 transition suitable for pumping of Eu:NaGd(WO4)2, the maximum cross-section is σabs = 1.2 × 10−21 cm2 at 535.5 nm with the full width at half maximum (FWHM) of 3.1 nm (at RT, for E || a polarization). For the 5D0 → 7F4 transition, the maximum stimulated-emission cross-section is σSE = 1.6 × 10−21 cm2 at 698.3 nm (RT, E || c polarization). Lifetime of the 5D0 state is 490 ± 10 μs (at RT). Under UV excitation, Eu:NaGd(WO4)2 provides intense red emission with CIE coordinates (x = 0.671, y = 0.329).

Spectroscopic properties of Er : LiLuF4 and Er : LiYF4 crystals in the spectral region near 1.5 μm and the lasing characteristics of these crystals under in-band pumping at a wavelength of 1522 nm are studied. With the Er : LiLuF4 crystal, the maximum slope efficiency with respect to the absorbed pump power was 44% at a wavelength of 1609 nm. Continuous-wave operation of an inband pumped Er : LiYF4 laser is obtained for the first time. The output power at a wavelength of 1606 nm was 58 mW with a slope efficiency of 21%.

We report on a comprehensive spectroscopic and laser characterization of monoclinic Yb,Tm:KLu(WO4)2 crystals. Stimulated-emission cross-section spectra corresponding to the 3F4 → 3H6 transition of Tm3+ ions are determined. The radiative lifetime of the 3F4 state of Tm3+ ions is 0.82 ms. The maximum Yb3+ → Tm3+ energy transfer efficiency is 83.9% for 5 at.% Yb – 8 at.% Tm doping. The fractional heat loading for Yb,Tm:KLu(WO4)2 is 0.45 ± 0.05. Using a hemispherical cavity and 5 at.% Yb – 6 at.% Tm doped crystal, a maximum CW power of 227 mW is achieved at 1.983–2.011 μm with a maximum slope efficiency η = 14%. In the microchip laser set-up, the highest slope efficiency is 20% for a 5 at.% Yb– 8 at.% Tm doped crystal with a maximum output power of 201 mW at 1.99–2.007 μm. Operation of Yb,Tm:KLu(WO4)2 as a vibronic laser emitting at 2.081–2.093 μm is also demonstrated.

Principal component analysis of temperature dependences of fluorescence spectra of Yb3+:Y3Al5O12 and Yb3+:CaF2 is used for determining the Stark structure of Yb3+ energy levels. The results obtained are in a good agreement with reference data determined by the conventional methods of absorption and time-resolved fluorescence spectroscopy at low temperatures.

Q-switched erbium lasers emitting in the 1.5–1.6 μm spectral region are widely used in laser rangefmders and LIBS systems. These applications require compact and low-cost sources of laser pulses with high average output power. Passive Q-switching is one of the most simple and reliable method to achieve the abovementioned requirements. Er, Yb:GdAl 3 (BO 3 ) 4 (Er, Yb:GdAB) crystal was shown to be an efficient laser material for the 1.5–1.6 μm spectral range [1]. Recently a passively Q-switched Er, Yb:GdAB laser was demonstrated with Co2+:MgAl 2 O 4 , graphene and SWCNT saturable absorbers [2-4]. Here we report Er, Yb:GdAB laser passively Q-switched by using of MBE-grown Cr:ZnS thin films.

DOI: 10.1016/j.optcom.2016.12.023 URL: http://www.sciencedirect.com/science/article/pii/S0030401816310847 Filiació URV: SI Inclòs a la memòria: SI We report on a model of diode-pumped Thulium lasers passively Q-switched by a graphene saturable absorber applicable also for any other ¿fast¿ saturable absorber. It reasonably predicts the dependence of the pulse duration, pulse energy and pulse repetition frequency on the absorbed power. The model is applied in the present work for a Tm: KLuW microchip laser passively Q-switched with a multi-layer graphene saturable absorber. The laser generates ~1 W at 1926 nm with a slope efficiency of 39%. Stable 190 ns /4.1 ¿J pulses are achieved at a pulse repetition frequency of 260 kHz. The potential of graphene for the generation of few-ns pulses at ~2 µm is discussed.

A series of new fluorophosphate glasses with small content of phosphates doped with various Nd3+ ions concentration for optical applications has been prepared and characterized. Based on Judd-Ofelt intensity parameters, radiative transition probability, radiative lifetime, branching ratio, and emission cross-section of Nd3+ions have been derived for all Nd3+concentrations.The effect of the glass rigidity and lead presence in glass composition on radiative properties have been estimated. The high emission cross-section (2.33×10−20 cm2) and large quantum efficiency (93%) both suggest the glass potential for compact 1.06-μm laser applications. The analysis of luminescence kinetics has shown the formation of neodymium ion clusters beginning from neodymium concentration of 1.006 × 1020 cm−3.

The influence of lead fluoride on the formation and luminescent properties of glass and glass-ceramics has been studied. Using the Judd-Ofelt theory, the intensity parameters Ωt have been obtained. The stimulated emission cross-section of the 4I13/2→4I15/2 transition has been determined. The energy transfer from ytterbium to erbium with 96% efficiency was found with an erbium laser level lifetime of ∼8 ms. The gain shape of the glass under study has been found to be smoother than for phosphate glasses, which makes the former very attractive gain material for ultra-short laser sources. For the first time, fluorophosphate glass-ceramics were obtained with nanocrystals doped with erbium and ytterbium ions.

A Ho:YAG ceramic microchip laser pumped by a Tm fiber laser at 1910 nm is passively Q-switched by single- and multi-layer graphene, single-walled carbon nanotubes (SWCNTs), and Crsup2+/sup:ZnSe saturable absorbers (SAs). Employing SWCNTs, this laser generated an average power of 810 mW at 2090 nm with a slope efficiency of 68% and continuous wave to Q-switching conversion efficiency of 70%. The shortest pulse duration was 85 ns at a repetition rate of 165 kHz, and the pulse energy reached 4.9 μJ. The laser performance and pulse stability were superior compared to graphene SAs even for a different number of graphene layers (n=1 to 4). A model for the description of the Ho:YAG laser Q-switched by carbon nanostructures is presented. This modeling allowed us to estimate the saturation intensity for multi-layered graphene and SWCNT SAs to be 1.2±0.2 and 7±1 MW/cmsup2/sup, respectively. When using Crsup2+/sup:ZnSe, the Ho:YAG microchip laser generated 11 ns/25 μJ pulses at a repetition rate of 14.8 kHz.

We report diode-pumped passively Q-switched Er, Yb:GdAl 3 (BO 3 ) 4 laser. By using of Co2+:MgAl 2 O 4 crystal as a saturable absorber Q-switched laser pulses with duration of 12 ns and maximum energy of 18.7 μJ at repetition rate of 32 kHz corresponded to the average output power of 0.6 W were obtained at 1550 nm under the continuous-wave pumping. In burst-mode of operation Q-switched laser pulses with the highest energy up to 44 μJ were realized with a pulse repetition rate of 6.5 kHz.

Compact Yb:KLu(WO4)2 and Yb:LuVO4 lasers diode-pumped at 978 nm are passively Q-switched by a single-layer graphene saturable absorber. The Yb:KLu(WO4)2 laser generated 165 ns/0.49 μJ pulses at 1030 nm with 170 mW average output power and 12 % slope efficiency. With the Yb:LuVO4 laser, 152 ns/0.83 μJ pulses were achieved. The output power reached 300 mW at 1024 nm, and the slope efficiency was 10 %. Laser operation in a plano-plano cavity is achieved with both crystals with thermal lensing playing a key role in their performance. A model describing graphene Q-switched Yb lasers is developed. Our results indicate the potential of graphene for passive Q-switching of ~1 μm bulk lasers.

A diode-pumped Tm,Ho:KLu(WO4)2 microchip laser passively Q-switched with a Cr:ZnS saturable absorber generated an average output power of 131 mW at 2063.6 nm with a slope efficiency of 11% and a Q-switching conversion efficiency of 58%. The pulse characteristics were 14 ns/9 μJ at a pulse repetition frequency of 14.5 kHz. With higher modulation depth of the saturable absorber, 9 ns/10.4 μJ/8.2 kHz pulses were generated at 2061.1 nm, corresponding to a record peak power extracted from a passively Q-switched Tm,Ho laser of 1.15 kW. A theoretical model is presented, predicting the pulse energy and duration. The simulations are in good agreement with the experimental results.

Trigonal langasite-type ordered silicate crystal Yb:Ca3NbGa3Si2O14 (Yb:CNGS) is a promising material for efficient ∼1 μm lasers. We report on the first passively Q-switched Yb:CNGS laser using Cr4+:YAG and V3+:YAG saturable absorbers (SAs) with a 976 nm volume-Bragg-grating-stabilized diode as a pump source. The laser crystal was a c cut 3 at.% Yb:CNGS grown by the Czochralski method. It was placed in a compact microchip-type laser cavity. With a Cr4+:YAG SA, very stable 62.2 μJ/4.4 ns pulses were achieved at a repetition rate of 22.5 kHz. The average output power was 1.40 W at 1015.3 nm, corresponding to a Q switching conversion efficiency of 90%. With the V3+:YAG SA, the pulse characteristics were 13.3 μJ/11.1 ns at a higher repetition rate of 68.4 kHz. The performance of the Yb:CNGS/Cr4+:YAG was numerically modeled showing a good agreement with the experiment.

A mixed fluoride crystal of LiLu0.65Y0.35F4 doped with Nd3+ ions was grown by the Bridgman–Stockbarger method. Polarized absorption and luminescence spectra as well as luminescence lifetime were measured at room temperature. Emission probabilities, branching ratios and radiative lifetime were studied within the Judd–Ofelt theory and the emission cross section spectra were calculated. Efficient continuous wave laser operation was demonstrated with the crystal. A maximum output power of 7.7 W and slope efficiency of 60% were achieved at 1047 nm for the TEM00 mode.

The spectroscopic properties of Tm, Ho:KYW crystals with different Ho concentrations were investigated. The diode-pumped microchip laser operation of Tm (5 at.%), Ho (0.5 at.%):KYW and Tm (5 at.%), Ho (1 at.%):KYW was demonstrated. The highest, to our knowledge, output power of 480 mW with slope efficiency of 31% for CW Tm (5 at.%), Ho (0.5 at.%):KYW microchip laser was obtained.

Stimulated-emission cross-section spectra are determined for the ~1.5 μm and 3 μm transitions of Er3+ ions in YSGG crystal. For the 4I11/2→4I13/2 channel, the maximum stimulated-emission cross-section σSE is 0.43×10−20 cm2 at 2797.1 nm. For the 4I13/2→4I15/2 channel, σSE=1.20×10−20 cm2 at 1532.8 nm. Due to the reabsorption loss, laser operation is expected at ~1644 nm. Radiative lifetimes of all excited states of the Er3+ ion from 4I13/2 to 2H9/2 and probabilities of radiative transitions from these states are determined using the Judd–Ofelt theory. Radiative lifetimes of the 4I13/2 and 4I11/2 excited states for Er3+ ions in YSGG are 7.73 ms and 9.75 ms, respectively. Non-radiative decay is analyzed for lower excited-states of Er3+ ions in YSGG.

A single-layer graphene saturable absorber is employed for passive Q-switching of an Er, Yb:GdAl3(BO3)4 (Er,Yb:GdAB) compact laser, representing the first Er-doped oxoborate laser Q-switched by graphene. This laser is based on a c-cut 1.8 at. % Er3+, 15 at. % Yb3+:GdAB crystal diode-pumped at 0.976 μm. It generates a maximum average output power of 360 mW at 1.55 μm with a slope efficiency of 23% (with respect to the incident power). Stable ∼1 μJ/130 ns pulses are achieved at a repetition rate of 400 kHz. This result represents, to the best of our knowledge, the shortest pulse duration ever achieved in bulk Er lasers Q-switched by 2D materials. Graphene is a promising material for generating nanosecond pulses at high repetition rates (MHz range) in Er-doped oxoborate lasers emitting in the eye-safe range at 1.5–1.7 μm.

We demonstrate a passively Q-switched Er,Yb:GdAl3(BO3)4 diode-pumped laser emitting near 1.5 µm. By using a single-walled carbon nanotube (SWCNT) as a saturable absorber, Q-switched laser pulses with energy of 0.8 µJ and duration of 130 ns at a maximum repetition rate of 500 kHz were obtained at 1550 nm.

A diode-pumped Yb:KLu(WO4)2 microchip laser passively Q-switched by a Cr4+:YAG saturable absorber generated a maximum average output power of 590 mW at 1031 nm with a slope efficiency of 55%. The pulse characteristics were 690 ps/47.6 μJ at a pulse repetition frequency of 12.4 kHz. The output beam had an excellent circular profile with M2

We report for the first time, to the best of our knowledge, on a diode-pumped passively Q-switched Er,Yb:GdAl3(BO3)4 laser. By using a Co2+:MgAl2O4 crystal as a saturable absorber, Q-switched laser pulses with a duration of 12 ns and a maximum energy of 18.7 μJ at a repetition rate of 32 kHz corresponding to an average output power of 0.6 W were obtained at 1550 nm under continuous-wave pumping. In the burst mode of operation, Q-switched laser pulses with the highest energy up to 44 μJ were realized with a pulse repetition rate of 6.5 kHz.

Inband-pumped Ho:YAG ceramic lasers emitting near 2.09 μm are passively Q-switched by mono- and multi-layered graphene, SWCNTs and Cr:ZnSe saturable absorbers. With SWCNTs, 85-ns, 4.9-μJ pulses are generated at a repetition rate of 165 kHz.

We report on the first Tm3+-doped double tungstate waveguide laser passively Q-switched by a graphene saturable absorber using a 12.4 µm-thick 3 at.% Tm:KY0.58Gd0.22Lu0.17(WO4)2 epitaxial layer grown on a (0 1 0)-oriented pure KY(WO4)2 substrate. This laser generated 5.8 nJ/195 ns pulses at 1831.8 nm corresponding to a pulse repetition frequency of 1.13 MHz. These are the shortest pulses achieved in passively Q-switched Tm waveguide lasers. The laser slope efficiency was 9% and the Q-switching conversion efficiency reached 45%. Graphene is promising for the generation of ns pulses at ~2 µm in Tm3+-doped double tungstate waveguide lasers operating in the MHz-range.