LuAG Crystal Research Articles

Comparative study of eye-safe Nd:LuAG crystal and ceramic lasers at 1.83 μm operating on 4F3/2 → 4I15/2 transition

We report on diode-pumped Nd:LuAG crystal and ceramic lasers operating at about 1.83 μm, using a simple and compact plane-concave cavity configuration. For Nd:LuAG crystal laser oscillating at 1828.43 nm, the maximum output power reaches 0.36 W with slope efficiency of about 5.0%. For Nd:LuAG ceramic laser, a maximum output power of 0.145 W is achieved with slope efficiency of about 2.2%, and the lasing wavelength peaks at 1828.76 nm. The 1.83-μm Nd laser sources could be very promising for eye-safe applications because they have stronger water absorption than another kind of eye-safe Nd lasers operating at 1.4 μm.

Enhanced emission of the 1.50–1.67 μm fluorescence in Er3+, Ce3+–codoped Lu3Al5O12 crystal

The use of Ce3+ codoping for enhancement of the Er3+: 4I13/2 → 4I15/2 emissions were investigated in the Lu3Al5O12 (LuAG) crystal for the first time. The effect of Ce3+ codoping on the 1.50–1.67 μm photoluminescence of Er3+ was investigated in detail. It was found that Ce3+ greatly enhanced Er3+: 1.50–1.67 μm emission by increasing the non-radiative decay rate from the 4I11/2 to 4I13/2 of Er3+, leading to greater population accumulation in the 4I13/2 level. With the codoped of Ce3+ ion in Er:LuAG crystal, the lifetime of Er3+: 4I11/2 level decreases dramatically from 90 μs to 58 μs, while the lifetime of Er3+: 4I13/2 level remains almost unchanged. These results suggest that the Er/Ce: LuAG crystal may become an attractive host for developing solid state lasers at around 1.50–1.67 μm laser applications under a conventional 970 nm LD pump.

Full investigation into continuous-wave Nd:LuAG lasers on ^4F_3/2→^4I_13/2 transition around 13 and 14 μm

We report a full investigation of continuous-wave diode-pumped Nd:LuAG single crystal lasers on 4F3/2→4I13/2 transition around 1.3 and 1.4 μm. In free-running mode, a maximum output power of 4.18 W is achieved for a simultaneous dual-wavelength laser operation at 1321 and 1338 nm, which represents the highest output power for Nd:LuAG laser material at a 1.3 μm emission band. Three single wavelength lasers at 1340, 1332 and 1322 nm, as well as a dual-wavelength laser at 1334 and 1338 nm, are also generated with maximum output powers of 2.39, 2.63, 2.24 and 1.23 W, respectively, with the aid of a glass etalon. Moreover, a single wavelength laser at 1353 nm is also obtained with a maximum output power of 1.53 W. Furthermore, in free-running mode, simultaneous tri-wavelength eye-safe lasers at 1419, 1432 and 1442 nm are attained with a maximum output power of 1.83 W, and a 1.08 W single wavelength laser at 1419 nm is also yielded. Most of the 1.3 μm lasers and all of the 1.4 μm lasers are demonstrated for the first time to our knowledge. Thus, this work indicates that Nd:LuAG crystal is a very promising laser gain medium for high-power continuous-wave infrared laser generation.

Energy Resolution of Ce:GAGG and Pr:LuAG Scintillators Coupled to $3 ~\rm {mm} \times 3 ~\rm {mm}$ Silicon Photomultipliers

Silicon Photomultipliers (SiPM) have shown great promise as a suitable replacement for conventional vacuum based Photomultiplier Tubes (PMT). Progress in recent years has been vast with SiPM sensors pushing the boundaries in energy and timing resolution as well as photon detection efficiency and active surface area. In this study we report the energy resolution and linearity of two novel scintillator crystals, Cerium doped Gd3Al2Ga3O12 (Ce:GAGG) and Praseodymium doped Lu3Al5O12 (Pr:LuAG), readout by three different types of $3\times 3~\mathrm {mm}^{2}$ silicon photomultiplier sensors produced by SensL (MicroFM, MicroFB, MicroFC). Such a scintillator-SiPM architecture has applications in pre-clinical and clinical medical imaging modalities such as Positron Emission Tomography (PET). N-on-P (M series), P-on-N (B series) and low-noise P-on-N (C series) versions of the SiPM sensor platform have been coupled to the crystals and the response characterized over a range of gamma energies and detector bias values. A saturation-corrected energy resolution of 11.7% was achieved for a MicroFM device coupled to a $3\times 3\times 30~\mathrm {mm}^{3}$ Ce:GAGG crystal at 20°C. An energy resolution of 16.1% was obtained for a MicroFB device optically coupled to to a $3\times 3\times 30~\mathrm {mm}^{3}$ Pr:LuAG crystal at 20°C.

Characterization of Pr:LuAG scintillating crystals for X-ray spectroscopy

The main features of the Pr doped Lu3Al5O12 (Pr:LuAG) scintillating crystals for X-ray spectroscopy applications have been studied using different radioactive sources and photo-detectors. Pr:LuAG is cheaper, compared to a Germanium detector, but with remarkable properties which make it useful for many applications, from fundamental physics measurements to the PET imaging for medical purposes: high density, elevate light yield, fast response, high energy resolution, no hygroscopicity. A sample of Pr:LuAG crystals with 14mm×14mm surface area and 13mm thickness and a NaI crystal of the same surface and 26mm thickness used as a reference have been characterized with several radioactive sources, emitting photons in the range 100–1000keV. Different light detectors were adopted for the Pr:LuAG studies, sensitive to its UV emission (peak at 310nm): a 3in. PMT (Hamamatsu R11065) and new arrays of Hamamatsu SiPM S13361, with siliconic resin as a window. Preliminary results are presented on the performance of the Pr:LuAG crystals, to be mounted in a 2×2 array to be tested in the 2015 run of the FAMU experiment at RIKEN-RAL muon facility. The goal is the detection of the X-rays (around 130keV) emitted during the de-excitation processes of the muonic hydrogen after the excitation with an IR laser with wavelength set at the resonance of the hyperfine splitting, to measure the muonic atom proton radius with unprecedented precision.

Athermal distributed Brillouin sensors utilizing all-glass optical fibers fabricated from rare earth garnets: LuAG

An all-glass optical fiber derived from single-crystal LuAG is investigated for its potential use in athermal Brillouin distributed strain sensors. Such sensor systems are comprised of fiber whose Brillouin frequency shift is independent of temperature, but not independent of strain. Bulk Brillouin spectroscopy measurements on the precursor LuAG crystal are performed to gain insight into the crystal-to-glass transition. Results suggest that both the mass density and acoustic velocity are reduced relative to the crystal phase, in common with the other rare earth aluminosilicates. Advantages of the LuAG derived fiber over other rare earth garnet-derived fibers for the sensing application are a stronger strain response and larger Brilloun gain with narrower Brillouin spectral width.

Thermal analysis and experimental study of end-pumped continuous-wave thulium-doped laser

Abstract This paper focused on the analysis of thermal effect of Tm:LuAG crystal and its lasing characteristics under continuous-wave (CW) operation at room temperature. The temperature-distribution of Tm:LuAG rod was shown intuitively by using a software of COMSOL. The thermal focal length was calculated which was useful to design the resonator. In experiment, thermal focal length of Tm:LuAG crystal was measured, firstly. The experimental results were coinciding with the theoretical calculations. Then, laser characteristics of CW Tm:LuAG crystal were measured. Maximum output power of 6.34 W was obtained when the pump power was 25.7 W. To our best knowledge, it was the highest output power of CW Tm:LuAG laser. The output wavelength was 2023 nm and the beam quality factor was M2 = 3.8 at the maximum power level.

Passively mode-locked Nd:LuAG laser at 1338 nm

A stable passive mode-locking Nd:LuAG laser at 1338 nm with a semiconductor saturable absorber mirror (SESAM) is demonstrated for the first time. The mode-locking Nd:LuAG laser yielded a maximum average output power of 0.54Wwith a slope efficiency of 10.2%. The corresponding shortest pulse duration was 18.3 ps with a signal-to-noise ratio of 63 dB under a pulse repetition rate of46.9MHz. This work indicates that the Nd:LuAG crystal is a promising candidate for realizing picosecond lasers around 1.3 μm spectral region.

760 fs diode-pumped mode-locked laser with Yb:LuAG crystal at 1032 nm.

In this study, we experimentally demonstrate the generation of 760fs pulse duration from a diode-pumped Yb:LuAG mode-locked laser at 1032nm. At the repetition rate of 58.6MHz, the maximum average power of 1.07W was obtained, corresponding to the peak power of 24kW. To our knowledge, these results represent the shortest pulse duration and highest peak power ever obtained for a 1032nm mode-locked laser with Yb:LuAG crystal.

Actively Q-switched laser performance of Nd:LuAG crystal with birefringence compensator

A laser diodes dual-end-pumped 1064 nm pulsed laser based on two Nd:LuAG crystal slabs using a quarter-wave plate to reduce depolarization loss is reported. The experimental results showed that both the degree of polarization and conversion efficiency increased. The electro-optic Q-switched operation was realized at a repetition rate of 500 Hz with single pulse energy of 13 mJ output. Its slope efficiency and optical-to-optical efficiency were 24 and 20 % respectively. The shortest pulse width of 9 ns was recorded, corresponding to an output peak power as high as 1.4 MW for each pulse. The beam quality factors of the pulsed laser were \( {\text{M}}_{\text{x}}^{2} = 1.7 \) and \( {\text{M}}_{\text{y}}^{2} = 1.85 \).

Experimental and theoretical study of a passively Q-switched Nd:LuAG laser at 13 μm with a V^3+:YAG saturable absorber

We report the characteristics of a diode-pumped continuous-wave (CW) and passively Q-switched Nd:LuAG laser emitting 1.3 μm wavelength. A maximum average output power of 954 mW was obtained under CW operation, giving a slope efficiency of 14.7%. With an V3+:YAG crystal wafer employed as saturable absorber, the passively Q-switched Nd:LuAG laser produced a minimum pulse duration of 17 ns under a repetition rate of 8 kHz, and a maximum single pulse energy of 18.9 μJ. A rate equation model is introduced to theoretically analyze the results obtained in the experiment, in which the Gaussian spatial distribution of the intracavity photon density and the longitudinal distribution of the photon density along the cavity axis are taken into account. The results of numerical calculations of the rate equations are consistent with the experimental results. The results indicated the Nd:LuAG crystal as a promising gain medium for achieving short pulses with high energy at 1.3 μm.

1.21 W passively mode-locked Tm:LuAG laser.

A watt-level output passively mode-locked Tm:LuAG bulk laser with an InGaAs semiconductor saturable absorber mirror (SESAM) is demonstrated for the first time. A maximum average output power of 1.21 W at 2022.9 nm has been achieved with a pulse duration of 38 ps and a repetition rate of 129.2 MHz. The results indicate the potential of Tm:LuAG crystals as candidate for realizing high power ultrafast lasers at 2 μm.

Thermal lensing and laser performance of Tm:LuAG crystal at room temperature

In this paper, thermal effect of a diode-end-pumping Tm:LuAG crystal is analyzed and the lasing characteristics at room temperature are also investigated. Based on a thermal model, the thermal focal length of Tm:LuAG crystal is calculated at different pump energies between 50mJ and 300mJ. The sensitivity factor of the thermal lens M=d(1/f)/dPabs is estimated to be 0.36m−1/W or 36m−1/J. The thermal focal length of Tm:LuAG crystal is also measured at different pump energies. Results show that the experimental data are very well in accordance with the theoretical calculations. Laser characteristics of Tm:LuAG crystal at room temperature are also investigated. Under a pump energy of 300mJ, the maximum output energy of 41.0mJ is obtained, with a slope efficiency of 20.8%. The build-up time of the pulse is 2.76ms, and the beam quality factor is measured to be M2=1.17.

Sub-100ns passively Q-switched Nd:LuAG laser with multi-walled carbon nanotube

Abstract We report the first demonstration of a diode-pumped passively Q-switched Nd:LuAG laser with a multi-walled carbon nanotube (MWCNT) as saturable absorber. A maximum average output power of 844 mW and pulses as short as 78 ns under a repetition rate of about 100 kHz were generated. A MWCNT Q-switched Nd:YAG laser was comparatively investigated, in comparison with which the Nd:LuAG laser showed lower threshold absorbed pump power and higher pulse energy, indicating a better energy storage ability of Nd:LuAG crystal than Nd:YAG.

Development of a prototype of time-over-threshold based small animal PET scanner

A time-over-threshold (ToT)-based positron emission tomography (TODPET) scanner was designed and fabricated. The PET scanner consisted of eight block detectors, each of which is composed of a 12×12 array of 2×2×10mm3 Pr:LuAG crystals individually coupled with a 12×12 UV-enhanced avalanche photodiode (APD) array. The APDs were individually read out using a custom-designed time-over-threshold application-specific integrated circuit (ASIC) and field-programmable gate array (FPGA) readout system. The PET scanner has an energy resolution of 10% and a time resolution of 4.2ns. A spatial resolution of 1.17mm (FWHM) was demonstrated in the initial results.

A comparison of the laser performance of Yb3+:LuAG crystals with different doping levels

We present a study and a comparison of the laser performance achieved by using 10at.%, 15at.% at. and 20at.% Yb3+:LuAG crystals longitudinally pumped at 936 nm in quasi-continuous wave.

Experimental evidence of a nonlinear loss mechanism in highly doped Yb:LuAG crystal

We report a rigorous study of the spectroscopic, laser and thermal properties of a 10at.% and a 15at.% Yb:LuAG crystals. A loss mechanism is observed in the medium with the highest doping, pumped at 936 nm and 968 nm, as a sharp and dramatic decrease of the laser output power is measured at higher excitation densities. The nonlinearity of the loss mechanism is confirmed by the fluorescence data and by the thermal lens. In particular, the dioptric power of the thermal lens acquired at different pumping levels shows a strong deviation of the expected linear trend. Here we report the influence of both the concentration and the ion excitation density of Yb3+ on the output powers, the slope efficiencies and the thresholds. Conversely excellent results are achieved with the 10at.%, which does not show any loss mechanism as at 1046 nm it delivers 11.8 W with a slope efficiency of η(s) = 82%, which is, to the best of our knowledge, the highest value reported in literature for this material.

Time over threshold based multi-channel LuAG-APD PET detector

To achieve efficient signal processing, several time-based positron emission tomography (PET) systems using a large number of granulated gamma-ray detectors have recently been proposed. In this work described here, a 144-channel Pr:LuAG avalanche photodiode (APD) PET detector that uses time over threshold (ToT) and pulse train methods was designed and fabricated. The detector is composed of 12×12 Pr:LuAG crystals, each of which produces a 2mm×2mm×10mm pixel individually coupled to a 12×12 APD array, which in turn is connected pixel-by-pixel with one channel of a time over threshold based application-specific integrated circuit (ToT-ASIC) that was designed and fabricated using a 0.25μm 3.3V Taiwan Semiconductor Company complementary metal oxide semiconductor (TSMC CMOS) process. The ToT outputs are connected through a field-programmable gate array (FPGA) to a data acquisition (DAQ) system. Three front-end ASIC boards—each incorporating a ToT-ASIC chip, threshold control digital-to-analog converters (DACs), and connectors, and dissipating power at about 230mW per board—are used to read from the 144-channel LuAG-APD detector. All three boards are connected through an FPGA board that is programmed to calibrate the individual thresholds of the ToT circuits to allow digital multiplexing to form an integrated PET module with a measured timing resolution of 4.2ns. Images transmitted by this PET system can be successfully acquired through collimation masks. As a further implementation of this technology, an animal PET system consisting of eight gamma pixel modules forming a ring is planned.

Efficient Quasi-Three-Level Laser Operation of Nd:Gd:LuAG Crystal and Blue Light Generation

The quasi-three-level laser operation of Nd:Gd:LuAG crystal is reported for the first time. The maximum continuous-wave (CW) output power of over more than 3 W was obtained with an optical conversion efficiency of 40.0% and a slope efficiency of 55.5%. With Cr:YAG as the saturable absorber, the passively Q-switched laser was achieved with the maximum average output power, shortest pulse width and pulse energy of 820 mW, 21.3 ns, and 124 μJ, respectively. By using a type-II cut LBO crystal as the intracavity frequency doubler, the maximum output power of 802 mW for CW operation and 331 mW for passively Q-switched operation were achieved at the wavelength of 474 nm.

Quantitive Research of the Crystallinity of Pr Doped ${\rm Lu}_{3}{\rm Al}_{5}{\rm O}_{12}$

In this study, we investigated the relation between crystallinity and scintillation properties of Pr:LuAG crystals grown by Czochralski (Cz) method. The crystallinity was determined as the dislocation density using the X-ray rocking curve technique. The scintillation pulse-height spectra were collected under 662 keV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">137</sup> Cs γ-ray excitation to evaluate the light yield and energy resolution. It was confirmed that both the light yield and energy resolution correlates with the crystalinity; however, the other factors also have an influence.