KLuW Laser Research Articles

Efficient acousto-optically Q-switched compact Yb:KLuW laser with self-Raman conversion

We report, for the first time to our knowledge, on acousto-optically Q-switched operation of a compact Yb:KLu(WO4)2 crystal laser, demonstrated at pulse repetition frequencies ranging from 60 kHz down to 3 kHz. 5.03 W of average output power at 1040.2 nm was produced at 60 kHz, with optical-to-optical and slope efficiencies of 50% and 62%. Self-Raman conversion was realized at pulse repetition frequencies not higher than 50 kHz; a maximum Stokes output power of 0.25 W at 1138.2 nm was generated at 20 kHz while the fundamental output power reached 2.20 W, the self-Raman conversion efficiency was determined as 6.0%. The resulting Raman pulse energy, duration, and peak power were, respectively, 12.5 μJ, 2.1 ns, and 6.0 kW.

Efficient diode-pumped Er:KLu(WO4)2 laser at ∼1.61 μm.

We report on an efficient diode-pumped continuous-wave erbium-doped monoclinic double tungstate laser. It is based on a 1at.% Er3+:KLu(WO4)2 (Er:KLuW) crystal cut along the Ng optical indicatrix axis. The Er:KLuW microchip laser, diode pumped at 0.98μm, generates 268mW at 1.610μm with a slope efficiency of 30%. The output is linearly polarized (E||Nm), and the laser beam is nearly diffraction limited (Mp,m2<1.1). Spectroscopic properties of Er3+ in KLuW are also presented. The stimulated-emission cross-section σSE is 0.46×10-20 cm2 at ∼1.609 μm for E||Nm. The microchip Er:KLuW laser outperforms the commercial Er,Yb:glass.

Single-walled carbon nanotubes oust graphene and semiconductor saturable absorbers in Q-switched solid-state lasers at 2 µm

The superior performance of a saturable absorber (SA) based on randomly-oriented single-walled carbon nanotubes (SWCNTs) operating in the spectral region of their first fundamental transition E11 over a graphene-SA containing several (n = 3) carbon layers and a commercial semiconductor SA (SESA) for passive Q-switching of bulk thulium solid-state lasers is demonstrated. Using SWCNT-SA in a compact diode-pumped Tm:KLuW laser, a maximum average output power of 1.36 W is achieved at 1932–1944 nm corresponding to a slope efficiency of 41% and pulse characteristics of 48 ns/5.5 µJ which are superior to that for graphene-SA (123 ns/3.1 µJ) and SESA (61 ns/1.1 µJ). SWCNT-SAs are promising for eye-safe miniature lasers at ~2 µm generating nanosecond pulses in the MHz repetition frequency range.

Ho:KLu(WO&lt;sub&gt;4&lt;/sub&gt;)&lt;sub&gt;2&lt;/sub&gt; Microchip Laser Q-Switched by a PbS Quantum-Dot-Doped Glass

We report on passive Q-switching of a Ho:KLu(WO4)2 (Ho:KLuW) microchip laser in-band-pumped by a Tm:KLuW laser at $\sim 1.96\mu \text{m}$ . As a saturable absorber, PbS-quantum-dot-doped glass was used which exhibits a saturation intensity of $\sim 3$ MW/cm $^{\mathrm {{2}}}$ near 2 $\mu \text{m}$ . Maximum average output power of 84 mW was achieved from the Ho laser at 2.061 $\mu \text{m}$ with a slope efficiency of 42% (with respect to the absorbed pump power). The shortest pulse duration was 30 ns. In the continuous-wave mode, the maximum output power of the Ho laser reached 530 mW at 2.08 $\mu \text{m}$ with a slope efficiency of 88%.

Single-layer graphene saturable absorber for diode-pumped passively Q-switched Tm:KLu(WO4)2 laser at 2 μm

We demonstrate a diode-pumped passively Q-switched Tm-laser emitting near 2 μm using single-layer graphene as the saturable absorber. The commercially available graphene samples were characterized by Raman spectroscopy and pump–probe measurements indicating high quality layered graphene. The Q-switched Tm:KLuW laser generated maximum pulse energy of ~1 μJ with a slope efficiency of 11%. The maximum average output power was 34 mW at a repetition rate of 35 kHz.

Ho:KLuW microchip laser intracavity pumped by a diode-pumped Tm:KLuW laser

A compact intracavity-pumped microchip Ho laser is realized using stacked Tm:KLuW/Ho:KLuW crystals pumped by a laser diode at 805 nm; both crystals are cut for light propagation along the N g optical indicatrix axis and emit with polarization along the N m axis. Maximum CW output power of 285 mW is achieved at a wavelength of 2080 nm for 5.6 W absorbed pump power in the Tm:KLuW crystal with a maximum slope efficiency of 8.3 %. Maximum total (Tm3+ and Ho3+ emission) output of 887 mW with a slope efficiency of 23 % is achieved. Laser operation is obtained in the 1867–1900 nm spectral range corresponding to the Tm emission, while Ho emits at 2078–2100 nm, depending on the output coupling. The microchip Ho laser generates a near-circular output beam with M 2 < 1.1. The compact laser setup with plane–plane cavity provides automatic mode-matching condition for the Tm and Ho laser modes.

In-band-pumped Ho:KLu(WO4)2 microchip laser with 84% slope efficiency.

We report on a continuous-wave Ho:KLu(WO4)2 (KLuW) microchip laser with a record slope efficiency of 84%, the highest value among the holmium inband-pumped lasers, delivering 201 mW output power at 2105 nm. The Ho laser operating at room temperature on the (5)I8→(5)I7 transition is in-band-pumped by a diode-pumped Tm:KLuW microchip laser at 1946 nm. Ho:KLuW laser operation at 2061 and 2079 nm is also demonstrated with a maximum slope efficiency of 79%. The microchip laser generates an almost diffraction-limited output beam with a Gaussian profile and a M2<1.1. The laser performance of the Ng-cut Ho:KLuW crystal is very similar for pump light polarizations ‖Nm and Np. The positive thermal lens plays a key role in the laser mode stabilization and proper mode-matching. The latter, together with the low quantum defect under in-band-pumping (∼0.08), is responsible for the extraordinary high slope efficiency.

Investigation of the KLu(WO4)2 crystal as an acousto-optic material

A KLuW laser crystal is investigated as an acousto-optic material. It is shown that the crystal can be used in devices for controlling high-power laser radiation. Obtainable characteristics of promising classical devices (modulator, deflector) are estimated. A possibility of developing a new type of device for both lasing and Q-switching is analyzed.

Carbon nanostructure-based saturable absorber mirror for a diode-pumped 500-MHz femtosecond Yb:KLu(WO4)2 laser.

We report a diode-pumped Yb:KLu(WO(4))(2) (Yb:KLuW) laser passively mode-locked by employing a carbon nanostructure-based multi-functional saturable absorber mirror. Two types of carbon nanostructures, single-walled carbon nanotubes (SWCNTs) and graphene, were deposited on a single dielectric mirror and applied both for stable mode-locking of the Yb:KLuW laser near 1050 nm in a compact cavity configuration. The carbon nanostructure mode-locked laser delivers 157-fs pulses with output powers of up to 85 mW at a repetition rate of 500 MHz.

Graphene mode-locked femtosecond Yb:KLuW laser

Large-area monolayer graphene, synthesized by chemical vapor deposition, was transferred to a 1-in. quartz substrate. The high-quality monolayer graphene has been subject to characterization of the nonlinear properties near 1 μm and was successfully applied as saturable absorber for passive mode-locking of a femtosecond Yb:KLuW laser. The diode-pumped mode-locked Yb:KLuW laser was tunable around 1.04 μm and delivered pulses as short as 160 fs. The maximum output power of 160 mW was demonstrated for 203 fs pulse duration. The mode-locked laser results are comparable to those demonstrated with the same laser gain medium using single-walled carbon nanotubes as saturable absorbers.

Passive mode locking of Yb:KLuW using a single-walled carbon nanotube saturable absorber

Mode locking of an Yb-doped bulk laser in the 1 microm spectral range using a single-walled carbon nanotube saturable absorber (SWCNT-SA) is demonstrated for the first time, to our knowledge. Passive mode locking of an Yb:KLuW laser resulted in nearly transform-limited pulses as short as 115 fs at 1048 nm. In addition, the nonlinear response of the SWCNT-SA was measured, yielding a modulation depth of 0.25% and a relaxation time of 750 fs.

Passively Q-Switched Nd:KLuW Laser with Semiconductor SaturableAbsorber

We demonstrate a passively Q-switched Nd:KLuW laser with asemiconductor saturable absorber mirror (SESAM) at wavelength 1070 nm.At a pump power of 1.3 W, the pulse width is measured to be about 17 nswith repetition rate of 10 kHz and with the average output power of260 mW. To our knowledge, this is the first demonstration of Nd:KLuWused for passively Q-switched laser with an SESAM.

Growth and properties of KLu(WO4)2, and novel ytterbium and thulium lasers based on this monoclinic crystalline host

AbstractHigh‐quality crystals of monoclinic KLu(WO4)2, shortly KLuW, were grown with sizes sufficient for its characterization and substantial progress was achieved in the field of spectroscopy and laser operation with Yb3+‐ and Tm3+‐doping. We review the growth methodology for bulk KLuW and epitaxial layers, its structural, thermo‐mechanical, and optical properties, the Yb3+ and Tm3+ spectroscopy, and present laser results obtained in several operational regimes both with Ti:sapphire and direct diode laser pumping using InGaAs and AlGaAs diodes near 980 and 800 nm, respectively. The slope efficiencies with respect to the absorbed pump power achieved with continuous‐wave (CW) bulk and epitaxial Yb:KLuW lasers under Ti:sapphire laser pumping were ≈ 57 and ≈ 66%, respectively. Output powers as high as 3.28 W were obtained with diode pumping in a simple two‐mirror cavity where the slope efficiency with respect to the incident pump power reached ≈ 78%. Passively Q‐switched laser operation of bulk Yb:KLuW was realized with a Cr:YAG saturable absorber resulting in oscillation at ≈ 1031 nm with a repetition rate of 28 kHz and simultaneous Raman conversion to ≈ 1138 nm with maximum energies of 32.4 and 14.4 μJ, respectively. The corresponding pulse durations were 1.41 and 0.71 ns. Passive mode‐locking by a semiconductor saturable absorber mirror (SESAM) produced bandwidth‐limited pulses with duration of 81 fs (1046 nm, 95 MHz) and 114 fs (1030 nm, 101 MHz) for bulk and epitaxial Yb:KLuW lasers, respectively. Slope efficiency as high as 69% with respect to the absorbed power and an output power of 4 W at 1950 nm were achieved with a diode‐pumped Tm:KLuW laser. The slope efficiency reached with an epitaxial Tm:KLuW laser under Ti:sapphire laser pumping was 64 %. The tunability achieved with bulk and epitaxial Tm:KLuW lasers extended from 1800 to 1987 nm and from 1894 to 2039 nm, respectively.