Neodymium-doped Yttrium Lithium Fluoride Research Articles

Intracavity frequency doubling acousto-optic Q-switched high repetition rate high-energy Nd:YLF laser.

The ongoing advancement of Ti:sapphire femtosecond laser technology has drawn increasing attention to high repetition rate, high-energy green lasers as ideal pump sources for Ti:sapphire regenerative amplifiers. This study employed a neodymium-doped yttrium lithium fluoride (Nd:YLF) as the gain medium, supplemented with side-pumped laser diodes, acousto-optic Q-switching, and intracavity frequency doubling technologies. The results demonstrated a repetition rate ranging from 1-10kHz, a pulse width of less than 100ns, and a single pulse energy exceeding 50mJ at 527nm green light output. Furthermore, an operating stability (RMS) of ≤0.15% was maintained for 14h at a repetition rate of 1kHz and an output power of 40W.

Selective retina therapy with real-time feedback-controlled technology in central serous chorioretinopathy: a 24-month follow-up real-world prospective study.

Although central serous chorioretinopathy (CSC) treatment using selective retinal therapy (SRT) has presented favourable outcomes, no long-term studies with a real-world clinical practice regimen have been conducted. We performed a long-term assessment of CSC treatment using SRT with real-time feedback (RTF) technology. 50 patients (53 eyes) with CSC and more than a 1-month symptom duration were recruited and treated with SRT using a 1.7 µs pulse width, 527 nm neodymium-doped yttrium lithium fluoride (Nd:YLF) laser equipped with an RTF system. After 6 months of treatment, complete subretinal fluid resolution was achieved in 62% of the eyes. The mean best-corrected visual acuity (BCVA; logarithm of the minimum angle of resolution, mean±SD) improved slightly from 0.15±0.18 at baseline to 0.12±0.21 at 6 months (p=0.062). The central retinal thickness (CRT; mean±SD) was reduced significantly from 350.6±100.1 µm at baseline to 268.2±70.6 µm at 6 months (p<0.001). Long-term follow-up revealed significant improvements in BCVA, from 9 months until 24 months, and in CRT, from 1 month until 24 months. No treatment-related adverse events were observed during the 24-month follow-up period. Our results suggest that SRT with RTF technology is a long-term safe treatment with anatomical improvement for patients with CSC.

Comparison of non-reactive flow fields in conventional swirl-air combustion and swirl distributed combustion

Flow field distribution in traditional swirl flow and simulated distributed reaction swirl flow configuration was examined at 3 kHz frequency using high-speed Particle Image Velocimetry (PIV). Non-reactive flow field conditions in distributed reaction zones were fostered from the conventional swirl flow case using the designed inlet mixture preparation with CO2 dilution of the inlet airstream that corresponded to the combustion case at a heat release intensity of 5.72 MW/m3-atm. High-speed imaging of flow fields was performed at a framing rate of 3000 frames/s using a Neodymium-doped Yttrium Lithium Fluoride (Nd:YLF) laser beam at 527 nm wavelength to capture the Mie scattering images of the flow field. Mean flow velocity obtained from the post-processing of raw PIV images showed higher momentum flux injection in the swirl distributed flow zone case as compared to the normal swirl flow case. Enhanced velocity fluctuations were also observed in both the axial and radial direction for the distributed swirl flow case resulting in higher turbulence for the examined condition. The distributed swirl flow case showed a prominent corner recirculation zone along with higher flow entrainment within the recirculation zone. Enhanced interaction of average streamlines with vortices was found in the swirl distributed flow case. Increased turbulent fluctuation in the two different spatial directions was responsible for higher Reynolds stress distribution (u′v′) in the distributed flow case, indicating improved mixing behavior at lower global oxygen concentrations from the carbon dioxide (CO2) dilution, and showed different length scales of turbulent eddies. Furthermore, the spatial local Damkӧhler number values for distributed flow case (for its implication in reacting case) were found to be less than unity. The results showed a shorter flow timescale than the corresponding chemical timescales in distributed reaction zone. These results help support substantiating the difference of reaction regimes on the Borghi diagram (plot of velocity fluctuation/ laminar flame speed versus the integral length scale/ flame thickness) between the distributed reaction zone (that possesses thickened reaction zone) and conventional swirl reaction flow regimes having corrugated flamelet zone.

Evaluation of the Safety and Efficacy of Selective Retina Therapy Laser Treatment in Patients with Central Serous Chorioretinopathy.

PurposeTo assess the safety and efficacy of selective retina therapy (SRT) using a Q-switched neodymium-doped yttrium lithium fluoride laser with feedback systems in patients with idiopathic central serous chorioretinopathy (CSC).MethodsThis randomized clinical trial enrolled patients having at least 3-month symptom of CSC. From month 3 visit, all subjects in both groups were eligible for SRT retreatment if they showed persistent or recurrent subretinal fluid (SRF). The primary outcome was complete resolution of SRF by optical coherence tomography at 3 months after treatment. The secondary outcomes were changes in SRF, central macular thickness (CMT) and best-corrected visual acuity at the 1-, 3-, and 6-month examinations.ResultsSixty-eight CSC patients were included (SRT, 31; control, 37). After 1 and 3 months, complete resolution of SRF was achieved in 25.8% and 54.8% of SRT group and 17.6% and 35.1% of controls. The differences were not statistically significant (p = 0.424 and p = 0.142, respectively). However, mixed model for repeated measures analyses showed that the reduction of SRF and CMT were observed earlier in SRT group than in the sham group (least squares mean difference, −59.7 μm; 95% confidence interval, −98.2 to −21.2; p = 0.0029; least squares mean difference −67.0 μm; 95% confidence interval, −104.8 to −29.2; p = 0.0007, respectively). Significant reduction of SRF (≥50% reduction from baseline) was more frequently observed in SRT group (80.6%) than the sham group (44.1%) at month 1 (p = 0.007). Early reduction of SRF and CMT was more abundant in SRT group with symptom duration less than 6 months. Treatment related serious adverse events were not observed.ConclusionsSRT using a Q-switched neodymium-doped yttrium lithium fluoride laser with feedback system was safe in this trial and effective for early resolution of SRF in the CSC patients. Early intervention with SRT can be a safe alternative for patients with acute symptomatic CSC.

Temperature-Dependent Stimulated Emission Cross-Section in Nd3+:YLF Crystal.

Spectroscopic properties of neodymium-doped yttrium lithium fluoride were measured at different temperatures from 35 K to 350 K in specimens with 1 at% Nd3+ concentration. The absorption spectrum was measured at room temperature from 400 to 900 nm. The decay dynamics of the 4F3/2 multiplet was investigated by measuring the fluorescence lifetime as a function of the sample temperature, and the radiative decay time was derived by extrapolation to 0 K. The stimulated-emission cross-sections of the transitions from the 4F3/2 to the 4I9/2, 4I11/2, and 4I13/2 levels were obtained from the fluorescence spectrum measured at different temperatures, using the Aull–Jenssen technique. The results show consistency with most results previously published at room temperature, extending them over a broader range of temperatures. A semi-empirical formula for the magnitude of the stimulated-emission cross-section as a function of temperature in the 250 K to 350 K temperature range, is presented for the most intense transitions to the 4I11/2 and 4I13/2 levels.

Residual stress distribution and surface geometry of medical Ti13Nb13Zr alloy treated by laser shock peening with flat-top laser beam

The metallic implants made of Ti13Nb13Zr alloy are usually used under the action of the cyclic loads conditions and fatigue failure occurs occasionally. Laser shock peening (LSP) is an innovative surface treatment process, which has been used to improve the fatigue life of metallic materials. The present research was performed on the Ti13Nb13Zr alloy subject to laser modification in order to determine the effects on the residual stress distribution and surface geometry. A neodymium doped yttrium lithium fluoride (Nd: YLF) pulse laser with a flat-top beam was applied at three different overlapping rates (10%, 30%, 50%), laser pulse energies (5J, 6J, 7J), and impact times (1 impact, 2 impacts, 3 impacts), respectively. The residual stresses were determined by X-ray diffractometer with sin 2ψ method. Firstly, the 30% overlap was chosen by comparing the residual stresses induced by LSP with different overlapping rates. Then, the effects of laser energies and impact times on surface residual stresses, in-depth residual stresses, surface deformation, and surface roughness were investigated and compared. The results showed that the residual stresses, surface deformation, and surface roughness increase with the increasing laser energies and impact times. The effected layer depth of residual stress is about 1058 μm with the 6J laser energy.

Two-photon excited luminescence in POPOP under pulse-periodic laser excitation

The spectra of two-photon-excited luminescence were registered in a polycrystalline aromatic compound POPOP. The two-photon luminescence in this substance was excited by the second optical harmonic of a solid-state neodymium-doped yttrium lithium fluoride laser (λ = 527 nm) and a copper vapor laser (λ = 510.6 nm). It is shown that the intensity of two-photon-excited luminescence depends nonlinearly on the intensity of an exciting radiation. It has been established that the intensity of the two-photon-excited luminescence is comparable to the intensity of Raman scattering under certain excitation conditions.

Characterization of bioactive and nutraceutical compounds occurring in olive oil processing wastes.

Several bioactive compounds, including phenolic acids and secoiridoids, are transferred from olive drupes to olive oil during the first stage of production. Here, the characterization of these low molecular weight (LMW) compounds in olive oil and in closely related processing materials, like olive leaves (OL) and olive mill wastewaters (OMW), was faced up, for the first time, by matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry (TOF MS). A novel binary matrix composed of 1,8-bis(tetramethylguanidino)naphthalene (TMGN) and 9-aminoacridine (9AA) (1:1 molar ratio), displaying excellent ionization properties at low levels of laser energy, was employed in reflectron negative ion mode by a MALDI TOF/TOF system equipped with a neodymium-doped yttrium lithium fluoride (Nd:YLF) laser (345 nm). MS/MS experiments were performed by using ambient air as the collision gas. Four major secoiridoids typically present in olive oil, i.e., the aglycones of oleuropein and ligstroside, and oleacein and olecanthal at m/z 377.1, 361.1, 319.1 and 303.1, respectively, were detected in virgin olive oil (VOO) extracts, along with some of their chemical/enzymatic hydrolysis by-products, such as elenolic (m/z 241.1), decarboxymethyl-elenolic acids (m/z 183.1) and hydroxytyrosol (m/z 153.1). Besides oleuropein aglycone and oleacein, hydroxylated derivatives of decarboxymethyl-elenolic acid and hydroxytyrosol were evidenced in OMW. While oleuropein was confirmed in OL extracts, several interesting phenolic compounds, including hydroxytyrosol, were recognized in OMW. The proposed approach based on the use of a novel binary matrix for MALDI MS/MS analyses of LMW bioactive compounds can be considered a promising analytical tool for a rapid screening of the phenolic fraction in olive oils and related processing wastes.

Potassium titanyl arsenate based cascaded optical parametric oscillator emit at 2.5 µm derived by neodymium-doped yttrium lithium fluoride laser

We reported a potassium titanyl arsenate (KTA) based cascaded optical parametric oscillator (OPO). The secondary OPO signal light at 2.5 µm was obtained with two OPO processes in one non-critical phase matching cut KTA crystal. This cascaded OPO was driven by a Q-switched neodymium-doped yttrium lithium fluoride (Nd:YLF) laser at 1047 nm. Making full use of the negative thermal lens effect and long upper level fluorescence lifetime of Nd:YLF, signal power of 605 mW at 2503 nm was achieved with a pulse repetition frequency of 15 kHz and an incident diode pump power of 9.7 W. Therefore, the cascaded OPO derived by Q-switched Nd:YLF laser could provide high peak power pulsed laser emission in mid-infrared band.

Temporal Response of Dilute Nitride Multi-Quantum-Well Vertical Cavity Enhanced Photodetector

The temporal response characteristics of a GaInNAs-based vertical resonant cavity enhanced photodetector device are presented for operation at λ ≈ 1.3 μm. The absorption layers of the device are composed of nine 7-nm-thick Ga0.65In0.35N0.02As0.98 quantum wells and are sandwiched between top and bottom AlGaAs/GaAs distributed Bragg reflectors (DBRs). The temperature dependence of the transient photoconductivity (TPC) under different light intensities and bias voltages is reported. Photoluminescence measurements were also performed on structures with and without the top DBR to determine their optical response under continuous illumination. The response time was measured using excitation from a 1047-nm pulsed neodymium-doped yttrium lithium fluoride laser with pulse width of 500 ps and repetition rate of 1 kHz. The rise time of the TPC was 2.27 ns at T = 50 K, decreasing to 1.79 ns at T = 300 K. The TPC decay time was 25.44 ns at T = 50 K, decreasing to 16.58 ns at T = 300 K. With detectivity of $$ 2.28 \times 10^{10} \,{\hbox{cm}}\sqrt {\hbox{Hz}} / {\hbox{W}} $$ and noise-equivalent power of $$ 2.45 \times 10^{ - 11} \,{\hbox{W/}}\sqrt {\hbox{Hz}} $$ , the proposed device is faster and more sensitive with better signal-to-noise ratio compared with other GaInNAs-based resonant cavity enhanced photodetectors (RCEPDs) for operation at 1.3 μm.

Superbasic alkyl-substituted bisphosphazene proton sponges: a new class of deprotonating matrices for negative ion matrix-assisted ionization/laser desorption mass spectrometry of low molecular weight hardly ionizable analytes.

Here hardly ionizable and low molecular weight compounds are detected in negative ion mode by using novel superbasic proton sponges based on 1,8-bisphosphazenylnaphthalene (PN) as MALDI matrices. Among the selected proton sponges, 1,8-bis(trispyrrolidinophosphazenyl)naphthalene (TPPN) has shown the best behaviour as matrix since it allows the direct detection of intact cholesterol without derivatization also in real challenging samples. Very weakly acidic compounds such as sterols, steroids, fatty alcohols and saccharides were detected in reflectron negative ion mode by a MALDI TOF/TOF system equipped with a neodymium-doped yttrium lithium fluoride (Nd:YLF) laser (345nm) with typical mass accuracy of 10ppm. MS/MS experiments were performed by using ambient air as the collision gas. Contrary to traditional MALDI matrices, superbasic proton sponges allowed the easy deprotonation of an alcohol functional group without a previous chemical derivatization step. Experimental evidence indicates that analyte deprotonation is achieved in the condensed phase, i.e. PN superbasic proton sponges operate according to a recently proposed model named matrix assisted ionization/laser desorption (MAILD). A detection limit of 3pmol/spot of cholesterol (model compound) with a signal-to-noise ratio≥10 was typically obtained. For the first time, the usefulness of novel superbasic proton sponges is demonstrated for MALDI detection of hardly ionizable compounds such as sterols, steroids, fatty alcohols and saccharides. The leading candidate TPPN has been successfully applied for negative ion MAILD-MS analysis of cholesterol, fatty acids and phospholipids in egg yolk and brain tissue extracts. Copyright © 2016 John Wiley & Sons, Ltd.

Focus on lasers and imaging

Focus on lasers and imaging

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.

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).

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.

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.

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.

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...

Impulsive stimulated Raman transition on theBstate of iodine molecules via repulsive states

Impulsive Raman transition on the $B\text{ }^{3}\ensuremath{\Pi}({0}_{u}^{+})$ state of the iodine molecule is reported. Several rovibrational states in the $B$ state are populated with the second harmonics of a neodymium-doped yttrium lithium fluoride (Nd:YLF) laser ($\ensuremath{\le}250\text{ }\text{ns}$, 527 nm). The population alteration with $\ensuremath{\Delta}v=\ifmmode\pm\else\textpm\fi{}1$ and $\ifmmode\pm\else\textpm\fi{}2$ are induced with a Ti:sapphire laser ($\ensuremath{\sim}30\text{ }\text{fs}$, 780 nm, ${10}^{12}--{10}^{14}\text{ }\text{W}/{\text{cm}}^{2}$) and detected by the $B\text{\ensuremath{-}}X$ dispersed fluorescence spectrum. The alteration is attributed to the Raman transition on the basis of the spectral profile, the pressure dependence, and the laser power dependence. The observed Raman transition is concluded to be a continuum resonance Raman transition mediated by upper repulsive states. Competing dissociation and ionization processes are also discussed by analyzing the laser power dependence.

Two-color photoionization in xuv free-electron and visible laser fields

Two-photon ionization of atomic helium has been measured by combining femtosecond extreme-ultraviolet pulses from the free-electron laser in Hamburg (FLASH at DESY) with intense light pulses from a synchronized neodymium-doped yttrium lithium fluoride laser. Sidebands appear in the photoelectron spectra when the two laser pulses overlap in both space and time. Their intensity exhibits a characteristic dependence on the relative time delay between the ionizing and the dressing pulses and provides an inherent time marker for time-resolved pump-probe experiments. The measurements of the sidebands are in good agreement with theoretical predictions and allow for a direct analysis of two-photon ionization, free from processes related to interference between multiple quantum paths.