Yttrium Lithium Fluoride Research Articles

Selective Retina Therapy in Patients With Chronic Central Serous Chorioretinopathy: A Pilot Study.

We evaluated visual outcomes, changes of maximum macular thickness (MMT) and subretinal fluid (SRF), and safety in patients with chronic central serous chorioretinopathy (CSC) after treatment with selective retina therapy (SRT). Retrospective cohort study of patients with chronic CSC presenting to a university-based hospital from January 2014 through January 2015 was conducted. A total of 12 eyes of 12 patients with chronic CSC lasting for at least 3 months was recruited. The follow-up period ranged from 3 to 12 months. Following evaluation of test spots at temporal arcades, SRT (Q-switched neodymium-doped yttrium lithium fluoride [Nd:YLF] laser; wavelength, 527 nm, pulse duration, 1.7 microsececond) was applied to the surrounding areas of leakage observed on fluorescein angiogram and/or pigment epithelial detachment (PED). Changes in best-correct visual acuity (BCVA), MMT, and SRF and macular sensitivity (MS) by microperimetry (MP) were evaluated. Eyes received treatment in a mean of 3.83 spots at the pulse energy of 65 to 90 μJ. Mean BCVA (logMAR) improved from 0.23 ± 0.12 at baseline to 0.14 ± 0.13 at 3 months. MMT decreased from 341.4 ± 85.5 μm at baseline to 236.0 ± 57.9 μm at 3 months. SRF completely resolved in 75% (9 eyes) at 3 months. Large PEDs (2 eyes) were flattened at 3 months. Retreatment was performed in 4 eyes. MP showed no evidence of scotoma around SRT-treated lesions. SRT treatment targeting the surrounding area of leakage point showed favorable visual and structural outcomes in chronic CSC patients without the risk of scotoma.

Laser refrigeration of hydrothermal nanocrystals in physiological media

Coherent laser radiation has enabled many scientific and technological breakthroughs including Bose-Einstein condensates, ultrafast spectroscopy, superresolution optical microscopy, photothermal therapy, and long-distance telecommunications. However, it has remained a challenge to refrigerate liquid media (including physiological buffers) during laser illumination due to significant background solvent absorption and the rapid (∼ ps) nonradiative vibrational relaxation of molecular electronic excited states. Here we demonstrate that single-beam laser trapping can be used to induce and quantify the local refrigeration of physiological media by >10 °C following the emission of photoluminescence from upconverting yttrium lithium fluoride (YLF) nanocrystals. A simple, low-cost hydrothermal approach is used to synthesize polycrystalline particles with sizes ranging from <200 nm to >1 μm. A tunable, near-infrared continuous-wave laser is used to optically trap individual YLF crystals with an irradiance on the order of 1 MW/cm(2). Heat is transported out of the crystal lattice (across the solid-liquid interface) by anti-Stokes (blue-shifted) photons following upconversion of Yb(3+) electronic excited states mediated by the absorption of optical phonons. Temperatures are quantified through analysis of the cold Brownian dynamics of individual nanocrystals in an inhomogeneous temperature field via forward light scattering in the back focal plane. The cold Brownian motion (CBM) analysis of individual YLF crystals indicates local cooling by >21 °C below ambient conditions in D2O, suggesting a range of potential future applications including single-molecule biophysics and integrated photonic, electronic, and microfluidic devices.

Efficient Near-Infrared Quantum Cutting in Tm3+/Yb3+ Codoped LiYF4 Single Crystals for Solar Photovoltaic

Downconversion (DC) with emission of two near-infrared photons about 1000 nm for each blue photon absorbed was obtained in thulium (Tm3+) and ytterbium (Yb3+) codoped yttrium lithium fluoride (LiYF4) single crystals grown by an improved Bridgman method. The luminescent properties of the crystals were measured through photoluminescence excitation, emission spectra and decay curves. Luminescence between 960 and 1050 nm from Yb3+: 2F5/2→2F7/2 transition, which was originated from the DC from Tm3+ ions to Yb3+ ions, was observed under the excitation of blue photon at 465 nm. Moreover, the energy transfer processes were studied based on the Inokuti-Hirayama model, and the results indicated that the energy transfer from Tm3+ to Yb3+ was an electric dipole-dipole interaction. The maximum quantum cutting efficiency approached up to 167.5% in LiYF4 single crystal codoped with 0.49mol% Tm3+ and 5.99mol% Yb3+. Application of this crystal has prospects for increasing the energy efficiency of crystalline Si solar cells by photon doubling of the high energy part of the solar spectrum.

2.6 W diode-pumped actively mode-locked Tm:YLF laser

We have experimentally demonstrated an actively mode-locked laser with a Tm3+-doped yttrium lithium fluoride crystal (YLF). A continuous mode-locked regime was achieved using an acousto-optic modulator and a stable train of pulses with 149.3 MHz repetition rate, 170 ps pulse width and 2.6 W average output power at 1.91 µm in a nearly diffraction-limited beam was obtained. To the best of our knowledge, this is the first report on a diode-pumped actively mode-locked bulk thulium laser with a stable output.

100 mJ Q-switched neodymium-doped yttrium lithium fluoride laser with intracavity second harmonic generation and optimized neodymium-doped yttrium lithium fluoride crystal properties, applications, and performance results

We report on the first kilohertz 100 mJ 527 nm YLF laser on the market or in any laboratory. The laser is capable of operating from single shot to 10 kHz with pulse widths of 100 ns at 1 kHz and with an M2 value of 10–15. Its availability presents new opportunities for the ultrafast community and industrial applications. Employing it as the pump source for the ultrafast lasers, new forms of radiation such as extreme ultraviolet obtained via laser-driven high-harmonic generation can be generated. These forms of radiation can be used for time-resolved studies of fast and ultrafast phenomena, along with many other applications, including medical sciences, industrial applications, and more. Green solid-state lasers with long pulse duration are an excellent choice for annealing power devices, where dopant activation and damage healing occur over micron depths. Manufacturers are currently using green lasers for thin Si films on glasses and plastics for various large-area microelectronic applications. The newly developed high pulse energy Nd:YLF lasers can replace the currently employed excimer lasers for applications previously mentioned. Annealing of semiconductor materials is extremely important for the power industry as increases in pulse energy can lead to an increase of annealing exposure area. At the same time, the stability of the annealing temperature depends on pulse width. Short pulses are able to achieve higher temperatures fast, but cool quickly, while using longer pulses, lower temperatures are enabled, but with a more gradual heating and cooling. The pulse duration stability of the Nd:YLF laser makes it an excellent candidate for use in the annealing processes. Other applications of such high power/high pulse energy lasers are biomedical instrumentation (laser induced breakdown spectroscopy, laser induced fluorescence, flow cytometry, confocal laser scanning microscopy, optical tweezers), medical (dermatology and ophthalmology), defense (nonlethal visual disruption, illuminators), and fluid dynamics (particle image velocimetry).

Interferometric measurement of the temperature coefficient of the refractive index dn/dT and the coefficient of thermal expansion of Pr:YLF laser crystals

We report interferometric measurements of the temperature coefficient of the refractive index (dn/dT) and the coefficient of thermal expansion (α) of a praseodymium-doped yttrium lithium fluoride (Pr:YLF) crystal and of a fused silica reference sample. Our phase-resolved interferometric method yields a large number of data points and thus allows a precise measurement and a good error estimation. Furthermore, both dn/dT and α are obtained simultaneously from a single measurement which reduces errors that can occur in separate measurements. Over the temperature range from 20 °C to 80 °C, the value of dn/dT of Pr:YLF decreases from −5.2 × 10(−6)/K to −6.2 × 10(−6)/K for the ordinary refractive index and from −7.6 × 10(−6)/K to −8.6 × 10(−6)/K for the extraordinary refractive index. The coefficient of thermal expansion for the a-axis of Pr:YLF increases from 16.4 × 10(−6)/K to 17.8 × 10(−6)/K over the same temperature range.

Effect of electron focusing in x-ray sources using LiTaO3 crystals excited by neodymium-doped yttrium lithium fluoride laser light

The intensity of x-rays from a 15 mm-diameter metal target bombarded by electrons emitted from a LiTaO3 crystal is found to depend upon the distance, h, between the crystal and the target. The electron emission of the LiTaO3 crystal is generated by being excited with light from a neodymium-doped yttrium lithium fluoride laser. The x-ray intensity is highest for h = 6 mm, coinciding also with a minimum electron spot size. The coincidence of the minimum electron spot size and maximum x-ray intensity with the 15 mm-diameter target is a result of self-focusing of the electrons by the higher electric field at the edge of the cylindrical crystal. The maximum electron energy at h = 6 mm with 120 s of laser irradiation is 47 keV, which is estimated from the maximum energy of bremsstrahlung x-rays.

A graphene-based passively Q-switched Ho:YAG laser in-band pumped by a diode-pumped Tm:YLF solid-state laser

We report the first demonstration of a Ho:YAG (yttrium aluminum garnet) solid-state laser passively Q-switched via a graphene saturable absorber. The Ho:YAG laser was in-band pumped by a continuous wave diode-pumped Tm:YLF (yttrium lithium fluoride) laser. Double-layer graphene grown by chemical vapor deposition and transferred onto a thin quartz plate was fabricated as the saturable absorber. We observed basically stable Q-switched laser pulses at the center wavelength of 2096.5 nm with the shortest pulse width of 632 ns, a repetition rate of 43 kHz, and the single-pulse energy of 13.3 μJ. Our results illustrate that graphene can be used well as a saturable absorber in a Ho-doped solid-state laser at 2 μm wavelength.

Cooperative Down-Conversion Luminescence in $ \hbox{Tb}^{3+}/ \hbox{Yb}^{3+}$ Co-Doped $\hbox{LiYF}_{4}$ Single Crystals

Cooperative down-conversion (DC) with emission of two near-infrared photons for each blue photon absorbed was achieved in Tb3+/Yb3+ co-doped yttrium lithium fluoride single crystals grown by an improved Bridgman method. The luminescent properties of the crystals were investigated through photoluminescence excitation, emission spectra, and decay curves. With the excitation of Tb3+ ion by a 486 nm light, emission between 980 and 1030 nm from the Yb3+:2F5/2 → 2F7/2 transition was observed, and this emission originated from the DC between Tb3+ and Yb3+ ions. The energy transfer processes are studied based on the Inokuti-Hirayama's model, and the interaction between Tb3+ and Yb3+ is confirmed to be electric dipole-dipole. The large quantum cutting efficiency approaches up to 166.7% for 0.32 mol% of Tb3+ and 7.98 mol% of Yb3+ co-doped LiYF4, which is potentially used as a DC layer in silicon-based solar cells.

Growth and testing of vertical external cavity surface emitting lasers (VECSELs) for intracavity cooling of Yb:YLF

Optically-pumped vertical external cavity surface emitting lasers (VECSELs) have unique characteristics that make them attractive for use in intracavity optical cooling of rare earth doped crystals. We present the development of high power VECSELs at 1020nm for cooling ytterbium-doped yttrium lithium fluoride (Yb:YLF). The VECSEL structures use AlAs/GaAs distributed Bragg reflectors and InGaAs/GaAsP resonant periodic gain epitaxially grown by metal-organic vapor phase epitaxy. To achieve the necessary output power, we investigated thinning the substrate to improve the thermal characteristics. We demonstrated a VECSEL structure that was grown inverted, bonded to the heat sink, and the substrate removed by chemical etching. The inverted structure allows us to demonstrate 15W output with 27% slope efficiency. Wavelength tuning of 30nm around 1020nm was achieved by inserting a birefringent quartz window into the cavity. The window also narrows the VECSEL emission, going from a FWHM of 5nm to below 0.5nm at a pump power of 40W.

Energy transfer enhanced laser cooling in Ho^3+ and Tm^3+-codoped lithium yttrium fluoride

We report a theoretical scheme for laser cooling of solids based on energy transfer usually found in rare-earth codoped materials. The cooling scheme enables a large enhancement in the cooling efficiency with regard to the standard anti-Stokes fluorescence cooling. A Ho3+ and Tm3+-codoped low-phonon crystal (LiYF4) sample is investigated to find that the cooling efficiency increases, and then decreases with the increasing of the resonant absorption. The optimal cooling efficiency is predicted to exceed 5%. The maximum cooling power density could be promoted greatly by applying the codoped cooling scheme. The cooling scheme is also valid for other rare-earth (for example, Tm3+ and Er3+, or Er3+ and Yb3+) codoped materials.

A single-frequency, diode-pumped Nd:YLF laser at 657 nm: a frequency and intensity noise comparison with an extended cavity diode laser

We report on a continuous wave, diode-pumped, intracavity frequency-doubled Nd:YLF (yttrium lithium fluoride) single-frequency ring laser designed for high-resolution spectroscopy of the calcium intercombination transition at 657 nm. We measured its frequency modulation (FM) and amplitude modulation (AM) noise and compared it with an extended cavity diode laser (ECDL). The Nd:YLF laser has much lower FM noise, extending to 50 kHz in comparison with 5 MHz for the ECDL, and slightly higher AM noise, transferred from the pump diode laser. This characterization is important for the design of servo-systems for frequency or intensity stabilization, and also for quantum optics experiments. A Nd:YLF laser at 657 nm can become an attractive high-power ‘local oscillator’ for a calcium optical clock, with a fundamental ‘telecom wavelength’ that can be directly used for remote transfer in optical fibers.

An Nd:YLF laser Q-switched by a monolayer-graphene saturable-absorber mirror

We demonstrate Q-switched operation of a transversely diode-pumped Nd:YLF (yttrium lithium fluoride) laser using chemical vapour deposition-grown large-area monolayer graphene transferred to a dielectric saturable-absorber mirror (G-SAM). The resulting compact design operates at 1047 nm with 2.5 μs pulses in a 100% modulation Q-switch regime with an average and very stable output power of 0.5 W. Different cavity lengths have been employed and the results are compared against a theoretical model based on rate equations, evidencing the role of transverse pumping in the system. The model also reveals that monolayer graphene effectively leads to shorter and more powerful pulses compared to those with multilayer graphene. These results establish the potential of single-layer graphene for providing a reliable and efficient Q-switch mechanism in solid-state lasers.

Synthesis and efficient near-infrared quantum cutting of Pr3+/Yb3+ co-doped LiYF4 single crystals

Yttrium lithium fluoride single crystals doped with trivalent lanthanide ions Pr3+ and Yb3+ are prepared by an improved Bridgman method. X-ray diffraction, photoluminescence excitation, and emission spectra and decay curves are measured to investigate the structural and luminescent properties of the crystals. An efficient near-infrared quantum cutting downconversion from the crystals was observed. The downconversion involves the emission of two near-infrared photons for each blue photon absorbed at 480 nm via cross relaxation energy transfer from Pr3+ to Yb3+. Decay curve fitting using a modified Inokuti-Hirayama expression indicates dipole-dipole energy transfer from Pr3+ to Yb3+, which is consistent with the expected cross-relaxation scheme. The maximum quantum cutting efficiency approaches up to 168.4% in LiYF4: 0.28 mol. % Pr3+ and 6.02 mol. % Yb3+, and this is equivalent to 68.4% energy transfer efficiency.

An atomistic surface simulation study predicting morphologies and segregation in yttrium lithium fluoride

The aim of this research on the laser material yttrium lithium fluoride (YLiF4) is to provide the first study of its surface structure, morphology and the properties of rare-earth doped surfaces. The study utilises the METADISE computer code to model the surfaces using interatomic potentials. Equilibrium and growth morphologies are predicted and a detailed profile of segregation of rare-earth dopants to the three dominating surfaces is given. The (001), (011) and (112) surfaces dominate the morphology. Rare-earth dopants La to Sm show segregation to these surfaces, with the (112) surface being of particular interest. As this work demonstrates, it is likely to have dopants clustered towards it.

Evanescent coupling in buried planar waveguide arrays written by a femtosecond laser in neodymium-doped yttrium lithium fluoride (Nd : YLiF4)

We report on the fabrication of buried planar waveguide arrays in neodymium-doped yttrium lithium fluoride (Nd : YLiF4) by femtosecond laser writing. With optimized fabrication parameters, the individual waveguide modes are coupled to each other through the evanescent tails of adjacent guided fields, while the coupling constant is calculated to be 1.18 cm−1 at 633 nm based on coupled-mode theory, which shows good agreement with the experiment results. Micro-luminescence spectra reveal that the Nd3+ fluorescence properties are not significantly affected by the waveguide formation processing, which indicates a fairly good potential for further laser actions in a compact device.

Power scalability and frequency agility of compact terahertz source based on frequency mixing from solid-state lasers

We investigate power scalability and frequency agility of a terahertz (THz) source by mixing two frequencies generated by solid-state lasers in a nonlinear crystal. They are made possible by introducing two solid-state laser crystals sharing the same Q switch and output coupler with the same laser beams decoupled to each other by a polarizer. Following the optimization, we have improved the THz output power nearly fivefold at 1.64 THz. By replacing one of the neodymium-doped lithium yttrium fluoride crystals with a neodymium-doped yttrium aluminum garnet crystal, we have produced 2.1 μW at 2.98 THz.

Study of the Powerful Nd:YLF Laser Amplifiers for the CTF3 Photoinjectors

A high-power neodymium-doped yttrium lithium fluoride (Nd:YLF) mode-locked 1.5-GHz laser currently used to drive the two photoinjectors of the Compact Linear Collider Test Facility project at the European Organization for Nuclear Research is described. A phenomenological characterization of the two powerful Nd:YLF amplifiers is presented and compared with the measurements. The laser system operates in a saturated steady-state mode. This mode provides good shot-to-shot stability with pulse train mean power in the 10 kW range.

Energetic Bessel–Gauss pulses from diode-pumped solid-state lasers

We discuss the generation of Bessel–Gauss pulses directly from a diode-pumped solid-state laser. The laser resonator has a plano–concave configuration with the concave end mirror replaced with a diffractive phase element. As the active material, Nd-doped yttrium lithium fluoride (YLF) and GdVO4 crystals have been used. The pulsed operation is obtained by passively Q-switching the laser using Cr4+:yttrium aluminum garnet (YAG) crystals with different unsaturated transmission coefficients. When guiding the pulses out from the resonator through the laser crystal, 5–10 ns long pulses with energies of 40–50 μJ and peak powers on the order of 10 kW are obtained. Even 70 μJ is possible, but this is achieved at the expense of slightly deteriorated beam quality in the far field.

Selective retina therapy for acute central serous chorioretinopathy

AimsTo evaluate selective retina therapy (SRT) as a treatment of acute central serous chorioretinopathy.Methods30 eyes of 30 patients with central serous chorioretinopathy of at least a 3 months' duration were...