Semiconductor saturable absorber Q-switching of a holmium micro-laser.

We report on a Holmium micro-laser passively Q-switched by a semiconductor saturable absorber (SSA), for the first time to the best of our knowledge. It is based on a 1 at.% Ho:YAG ceramic with good energy storage capability and several commercial transmission-type SSAs with 0.24% modulation depth. Under in-band pumping by a Tm fiber laser at 1910 nm, the Ho micro-laser generated 450 mW at 2089 nm with 37% slope efficiency. Stable 89 ns, 3.2 µJ pulses are achieved at a repetition rate of 141 kHz. Further shortening of the laser pulses is feasible with the increase of the modulation depth of the SSA while power scaling may lead to Q-switching at MHz-range repetition rates.

First laser emission of Yb0.15:(Lu0.5Y0.5)3Al5O12 ceramics.

We report the first laser oscillation on Yb0.15:(Lu0.5Y0.5)3Al12 ceramics at room temperature. At 1030 nm we measured a maximum output power of 7.3 W with a corresponding slope efficiency of 55.4% by using an output coupler with a transmission of T = 39.2%. The spectroscopic properties are compared with those of the two parent garnets Yb:YAG and Yb:LuAG. To the best of our knowledge these are the first measurements reported in literature achieved with this new host.

Spectroscopic and laser characterization of Yb0.15:(LuxY1-x)3Al5O12 ceramics with different Lu/Y balance.

We report a broad comparative analysis of the spectroscopic and laser properties of solid solution Lutetium-Yttrium Aluminum Garnet (LuYAG, (LuxY1-x)3Al5O12) ceramics doped with Yb. The investigation was mainly aimed to assess the impact of the Lu/Y ratio on the Yb optical and laser properties. Therefore we analyzed a set of samples with different Y/Lu balance, namely 25/75, 50/50 and 75/25, with 15% Yb doping. We found that the Yb absorption and emission spectra changed from YAG to LuAG when gradually increasing in Lu content. Regarding the laser emission, remarkable results were achieved with all samples. Maximum output power was 8.2 W, 7.3 W and 8.7 W for Y/Lu balance 25/75, 50/50 and 75/25 respectively, at 1030 nm; the slope efficiency and the optical-to-optical efficiencies approached or exceeded 60% and 50% respectively. The tuning range was investigated using an intracavity ZnSe prism. The broadest tuning range (998 nm to 1063 nm) was obtained with Y/Lu balance 75/25, whereas the emission of the other two samples extended from 1000 nm to 1058 nm. To the best of our knowledge, this is the first comparative analysis of Yb:LuYAG ceramics or crystals as laser host across such a broad range of Y/Lu ratios.

Diode-pumped tape casting planar waveguide YAG/Tm:YAG/YAG ceramic laser at 2013.76 nm.

We demonstrated the efficient guided laser action in a diode-pumped YAG/Tm:YAG/YAG ceramic planar waveguide fabricated by nonaqueous tape casting and solid-state reactive sintering technology for the first time, to the best of our knowledge. In the experiment, a maximum output power of 173 mW at a center wavelength of 2013.76 nm was obtained under an incident pump power of 10.3 W, corresponding to a slope efficiency of 3.0%. The beam quality M2=1.5 in a horizontal direction was measured at the highest output power.

Resonantly pumped actively mode-locked Ho:YAG ceramic laser at 2122.1 nm.

We discuss what we believe is the first continuous-wave mode-locked Ho:YAG ceramic laser. We produced a mode-locked pulse using an acousto-optic modulator. We used a 1.91 µm Tm-fiber laser as the pump source. At the incident pump power of 11.4 W, we achieved the maximum output power of 1.84 W at 2122.1 nm in a continuous-wave mode-locked regime. We obtained a short-duration pulse of 241.5 ps at a repetition frequency of 82.15 MHz and achieved the beam quality factor M² of 1.2. In addition, the maximum single pulse energy was 22.4 nJ.

YAG:Ce/(Gd,Y)AG:Ce dual-layered composite structure ceramic phosphors designed for bright white light-emitting diodes with various CCT.

Y3Al5O12:Ce and (Gd,Y)3Al5O12:Ce ceramic phosphors were fabricated by solid-state reaction method under vacuum sintering. Pure garnet phase of these (Gd,Y)AG:Ce ceramics was confirmed by X-ray diffraction (XRD) with Gd content of 0, 25%, 50% and 75%, respectively. The electroluminescent properties of the unpacked and packed LED devices based on YAG:Ce and (Gd,Y)AG:Ce ceramics were measured. The highest luminous efficacy of 130.5 lm/W was achieved by YAG:Ce ceramic phosphor with thickness of 0.4 mm. However, the correlated color temperature (CCT) of the LED device based on it was high due to a lack of red component in the emission light. Therefore, Y3Al5O12:Ce/(Gdx,Y1-x)3Al5O12:Ce dual-layered composite structure ceramics phosphor were designed and fabricated according to the color space chromaticity diagram. In one demonstration, various CCT could be tuned from 3100 K to 3600 K by these dual-layered structure, while the luminous efficacy can reach 109.9 lm/W. The high luminous efficacy and safe warm white light emitted by these dual-layered phosphors made them promising candidate for white LED devices.

Multiple-beam, pulse-burst, passively Q-switched ceramic Nd:YAG laser under micro-lens array pumping.

A novel four-beam (named laserI, laser II, laser III and laser IV, respectively), passively Q-switched, pulse-burst ceramic Nd:YAG laser under 2 × 2 micro-lens array pumping was demonstrated for the purpose of laser-induced plasma ignition (LIPI). Multiple-beam output together with pulse-burst mode in which both high repetition rate and high pulse energy can be realized simultaneously were obtained to greatly improve the performance of LIPI. The pulse-burst contained a maximum of 5 pulses, 3 pulses, 2 pulses and 3 pulses for laserI, laser II, laser III and laser IV, respectively, and the corresponding repetition rate of laser pulses in pulse-burst was 10.8 kHz, 7.2 kHz, 6.8 kHz and 5.2 kHz, respectively. The output energy for single laser pulse in pulse-burst was in the range of 0.12 mJ to 0.22 mJ.

GaSb-based SESAM mode-locked Tm:YAG ceramic laser at 2 µm.

Tunable and mode-locked laser operation near 2 µm based on different Tm-doped YAG ceramics, 4 at.% and 10 at.%, is demonstrated. Several designs of GaSb-based surface-quantum-well SESAMs are characterized and studied as saturable absorbers for mode-locking. Best mode-locking performance was achieved using an antireflection-coated near-surface quantum-well SESAM, resulting in a pulse duration of ~3 ps and ~150 mW average output power at 89 MHz. All mode-locked Tm:YAG ceramic lasers operated at 2012 nm, with over 133 nm demonstrated tuning for continuous-wave operation.

High-power Cr2+:ZnS saturable absorber passively Q-switched Ho:YAG ceramic laser and its application to pumping of a mid-IR OPO.

We used the Cr2+:ZnS as a saturable absorber to obtain a passively Q-switched Ho:YAG ceramic laser operating near 2.1 µm. The maximum average output power of 14.8 W and a shortest pulse width of 29 ns were obtained, and to our knowledge, this is the best report for the PQS Ho:YAG ceramic laser. A maximum energy per pulse of 0.6 mJ with a maximum pulse repetition frequency of 24.4 kHz was achieved, which corresponded to a peak power of 20 kW. We first used the PQS laser as the pump source of optical parametric oscillator to obtain the mid-infrared laser. A maximum average output power of 4.4 W was achieved from the ZnGeP2 parametric oscillator, corresponding to a slope efficiency of 49.5% with respect to the incident pump power.

Continuous-wave yellow-green laser at 0.56 µm based on frequency doubling of a diode-end-pumped ceramic Nd:YAG laser.

We present what is, to the best of our knowledge, the first report on yellow-green laser generation based on the frequency doubling of the 1.1 µm transitions in Nd:YAG ceramics. By employing an 885 nm diode laser as the end-pumping source and a lithium triborate crystal as the frequency doubler, the highest continuous wave output powers of 1.4, 0.5, and 1.1 W at 556, 558, and 561 nm are achieved, respectively. These result in optical-to-optical efficiencies of 6.9%, 2.5%, and 5.4% with respect to the absorbed pump power, respectively.

Comparison of laser induced thermal fracture between polycrystalline ceramic and crystal Nd:YAG.

Continuous wave 808 nm pump laser-induced thermal damage of polycrystalline transparent ceramic and crystalline Nd:YAG materials was investigated both experimentally and theoretically. The measured temperature agrees well with the theoretical simulation, and the maximum hoop stresses occur on the incident facet of the end-pumped rod at about √2 times of the pump beam radius w0, where the temperature gradient is the highest and the damage occurs first at this location. The fracture-limited laser intensity of ceramics was experimentally measured to be 6.4±0.6 kW/cm2, nearly 64% higher than that of the crystals (3.9±0.3 kW/cm2). The deduced thermal fracture stress for ceramic was 386±50 MPa, which is 64% higher than that of the crystals (235±16 MPa).

Hybrid ultra-short Yb:YAG ceramic master-oscillator high-power fiber amplifier.

We demonstrated a hybrid ceramic master-oscillator high-power fiber amplifier with a diode-pumped Yb:YAG ceramic laser as the seeding oscillator, which was passively mode-locked at 103.29 MHz repetition rate around 1031 nm by using a semiconductor saturable absorption mirror, and a two-stage double-clad photonic crystal fiber amplifier, which power-scaled the ceramic laser oscillator up to an average power of 303 W. The amplified pulses were further compressed to 237 and 418 fs at 50 and 150 W output powers, respectively. The compressed pulses exhibited about 0.05% deviation from the Gaussian fit, implying that the high-power fiber amplification induced neither observable temporal and spectral distortion nor significant nonlinear de-chirping of the chirped pulses.

Efficient Q-switched Tm:YAG ceramic slab laser.

Characteristics of Tm:YAG ceramic for high efficient 2-µm lasers are analyzed. Efficient diode end-pumped continuous-wave and Q-switched Tm:YAG ceramic lasers are demonstrated. At the absorbed pump power of 53.2W, the maximum continuous wave (cw) output power of 17.2 W around 2016 nm was obtained with the output transmission of 5%. The optical conversion efficiency is 32.3%, corresponding to a slope efficiency of 36.5%. For Q-switched operation, the shortest width of 69 ns was achieved with the pulse repetition frequency of 500 Hz and single pulse energy of 20.4 mJ, which indicates excellent energy storage capability of the Tm:YAG ceramic.

Combinatorial optimization of (Y(x)Lu(1-x-y))(3)Al(5)O(12):Ce(3y) green-yellow phosphors.

A combinatorial chemistry method was used to synthesize and screen (Y(x)Lu(1-x-y))(3)Al(5)O(12):Ce(3y) green-yellow phosphors. The material libraries were obtained using an inkjet delivery system and screened for their fluorescence under an ultraviolet light of 365 nm. The optimized composition was identified to be (Y(0.2)Lu(0.788))(3)Al(5)O(12):Ce(3+)(0.036). Scale-up experiments confirmed that the optimized composition of the phosphor showed the highest luminescence intensity and an excellent scintillation performance with a short decay time (<60 ns). The results indicated that the (Y(x)Lu(1-x-y))(3)Al(5)O(12):Ce(3y) could be potentially useful as green-yellow phosphors for ceramic scintillators.

Laser-diode pumped 40-W Yb:YAG ceramic laser.

We demonstrated a high-power continuous-wave (CW) polycrystalline Yb:YAG ceramic laser pumped by fiber-pigtailed laser diode at 968 nm with 400 mum fiber core. The Yb:YAG ceramic laser performance was compared for different Yb(3+) ion concentrations in the ceramics by using a conventional end-pump laser cavity consisting of two flat mirrors with output couplers of different transmissions. A CW laser output of 40 W average power with M(2) factor of 5.8 was obtained with 5 mol% Yb concentration under 120 W incident pump power. This is to the best of our knowledge the highest output power in end-pumped bulk Yb:YAG ceramic laser.

Electrical properties of multiwalled carbon nanotube reinforced fused silica composites.

Multiwalled carbon nanotube (MWCNT)-fused silica composite powders were synthesized by solgel method and dense bulk composites were successfully fabricated via hot-pressing. This composite was characterized by XRD, HRTEM, and FESEM. MWCNTs in the hot-pressed composites are in their integrity observed by HRTEM. The electrical properties of MWCNT-fused silica composites were measured and analyzed. The electrical resistivity was found to decrease with the increase in the amount of the MWCNT loading in the composite. When the volume percentage of the MWCNTs increased to 5 vol%, the electrical resistivity of the composite is 24.99 omega cm, which is a decrease of twelve orders of value over that of pure fused silica matrix. The electrical resistivity further decreases to 1.742 omega. cm as the concentration of the MWCNTs increased to 10 vol%. The dielectric properties of the composites were also measured at the frequency ranging from 12.4 to 17.8 GHz (Ku band) at room temperature. The experimental results reveal that the dielectric properties are extremely sensitive to the volume percentage of the MWCNTs, and the permittivities, especially the imaginary permittivities, increase dramatically with the increase in the concentration of the MWCNTs. The improvement of dielectric properties in high frequency region mainly originates from the greatly increasing electrical properties of the composite.

Ceramic planar waveguide laser of non-aqueous tape casting fabricated YAG/Yb:YAG/YAG.

Ceramic YAG/Yb:YAG/YAG planar waveguide lasers were realized on continuous-wave and mode-locked operations. The straight waveguide, fabricated by non-aqueous tape casting and solid state reactive sintering, enabled highly efficient diode-pumped waveguide continuous-wave laser with the slope efficiency of 66% and average output power of more than 3 W. The influence of the waveguide structure on the wavelength tunability was also experimentally investiccgated with a dispersive prism. Passively mode-locked operation of the ceramic waveguide laser was achieved by using a semiconductor saturable absorber mirror (SESAM), output 2.95 ps pulses with maximum power of 385 mW at the central wavelength of 1030 nm.

Combinatorial Optimization of (Lu1₋(x)Gd(x))3Al5O12:Ce3(y) yellow phosphors as precursors for ceramic scintillators.

A combinatorial chemistry method was employed to screen the yellow phosphors of (Lu1₋(x)Gd(x))3Al5O12:Ce3(y) as luminescent materials. An array of 81 compositions was synthesized by inkjetting nitrate solutions into microreactor wells and sintering at high temperature. The candidate formulations were evaluated by luminescence pictures, and the optimal composition was determined to be Lu(2.7)Gd(0.3)Al(5)O(12):Ce(0.045) after scale-up and detailed characterization. Lu2.7Gd0.3Al5O12:Ce0.045 was also found to have a short decay time (≤53.97 ns). These results demonstrate the great potential of the Lu2.7Gd0.3Al5O12:Ce0.045 as a component of ceramic scintillators.