Laser Heated Pedestal Growth Research Articles

Designing an all-laser processing and operating microheater conceptual device for medical applications

Obstructive sleep apnea (OSA) is a prevalent condition affecting a significant portion of the population, with a reported prevalence of 33% and 19% in males and females, respectively. OSA is associated with an increased risk of sudden death, with studies suggesting nearly double the risk compared to individuals without OSA. The condition is characterized by frequent sleep disruptions due to airway collapse, often at the level of the tongue or soft palate. Current treatment approaches primarily rely on radiofrequency (RF) ablation for tissue volume reduction. While effective, this technique can cause significant collateral damage and postoperative pain due to extensive burning of surrounding tissues. To avoid such drawbacks, in this work it is proposed and discussed the features of a possible conceptual all-laser-processing and operating device that can produce localized heat affected zones, with the possibility to monitor the local temperature during the procedure. The device is based on the eutectic composition of the system Al2O3-YAG, with double doping Nd3+ and Cr3+ crystalline fiber tip, which is prepared by the Laser-Heated Pedestal Growth technique on a sapphire single crystal fiber end. The results showed that the tip, although highly Nd3+-doped, follows the Jackson-Hunt relation for binary eutectic compounds. The lifetime of the luminescence produced by the Cr3+ doping, emitted by the eutectic tip, can act as a temperature sensor for the device in the range of 30 to 100 °C.

Characterization and mid-infrared laser operation in Er:CaF2 single crystal fiber grown by the laser heated pedestal growth method

Er:CaF2 crystals, characterized by low doping and high efficiency, are suitable materials for single-crystal fibers. 3 at.% Er:CaF2 single-crystal fibers (SCF) were grown using the laser heated pedestal growth (LHPG) method. Significant oxidation-induced whitening phenomena were observed during growth. Increasing the growth rate helped mitigate further deterioration due to oxidation. This is likely because higher growth speeds allow the SCF to quickly move away from temperature ranges conducive to oxidation. As oxidation progressed, the phonon energy of Er:CaF2 SCF increased, causing the emission intensity at ∼ 1 μm to decrease from 77 % in the initial source rod to 6 % in the fully whitened state. Additionally, the lifetime of the 4I11/2 level decreased by approximately 10 times, from 8.988 ms to 0.822 ms. Continuous laser output at ∼ 2.8 μm was achieved using the transparent portion of 3 at.% Er:CaF2 SCF. With an output mirror transmission of 2 %, a maximum output power of 251 mW and a slope efficiency of 15.9 % were obtained. Laser experiments demonstrated the potential application of LHPG-prepared Er:CaF2 SCF in ∼ 2.8 μm lasers, but further performance enhancement requires additional strategies to address oxidation issues. This work provides valuable insights into the preparation of Er:CaF2 SCF using the LHPG method.

Growth, spectroscopy properties, and laser operation of single crystal fiber: Nd3+-doped CNGG

Nd3+-doped calcium niobium gallium garnet single crystal fibers (Nd:CNGG SCFs) with varying Nd3+ concentrations were successfully grown using the laser-heated pedestal growth (LHPG) method. The study thoroughly examines the fundamental physical structure, optical properties, and laser characteristics of the as-grown Nd:CNGG SCFs. Results indicate that the Nd:CNGG SCF exhibits broader absorption and emission full width at half maximum (FWHM) compared to bulk single crystals. Moreover, pumped by a commercial 808 nm laser diode, continuous-wave laser operation at 1061 nm with a half-height width of 1.86 nm was achieved. The laser output power reached 1.04 W at an absorbed power of 7.46 W, with a slope efficiency of 25.4% relative to the absorbed pump power. These findings suggest that Nd:CNGG SCF holds promise as a practical and potent candidate for laser gain medium, offering significant research potential in the field of lasers.

First‐principle calculations, crystal growth, and broadband near‐infrared luminescence of Nd:Y2Mg3(SiO4)3 single crystal

AbstractThis study successfully grew Y2Mg3(SiO4)3 (YMS) single crystals doped with Nd3+ ions via laser heated pedestal growth method for the first time. Based on first‐principle calculations, the structural relaxation, energy band structure, density of states, and optical properties of YMS and Nd:YMS crystals with multiple disordered structures were calculated for the first time. The refractive index of the YMS crystal was obtained to be 1.83. The optical properties including absorption spectra, near‐infrared (NIR) luminescence spectra, and fluorescence lifetime at 1080 nm (Nd3+: 4F3/2→4I11/2) were characterized and analyzed based on the grown Nd:YMS single crystal. The crystal was found to have an ultra‐wide half‐height width (46.99 nm) of emission cross‐section, and a fluorescence lifetime of 220.38 µs, making it a luminescence material with excellent comprehensive performance.

Optical and scintillation properties of YAlO3:Ce scintillating single crystal fibers grown by laser heated pedestal growth method

Optical and scintillation properties of YAlO3:Ce scintillating single crystal fibers grown by laser heated pedestal growth method

Yb,Er,Tm:Sc2O3 single crystal fibers for multi-mode optical thermometry

Fluorescence intensity ratio (FIR) thermometers have obtained great attention in industrial production, medical diagnosis and scientific research. However, the sensitivity has a large decline at high temperatures, which seriously limits the practical applications. Here, the Yb,Er,Tm:Sc2O3 single crystal fibers were grown by laser-heated pedestal growth (LHPG) technique and its multi-mode FIR thermometry based on thermal coupled energy levels (TCLs) and non-thermal coupled energy levels (NTCLs) has been well demonstrated. The temperature measuring range of Yb,Er,Tm:Sc2O3 single crystal fibers covers 298–973 K, with an increase of 2 orders of magnitude in absolute sensitivity. The relative sensitivity is higher than 0.02 % K−1 in the whole T-range of 298∼973 K, with a maximum value of 1.02 % K−1. Especially at the high temperatures of 973 K, it can still maintain 0.31 % K−1. This work proposes an innovative fluorescence intensity ratio detection strategy to achieve complementary disadvantages between TCLs and NTCLs and provides an effective method for improving detection sensitivity.

Piezoelectric temperature acoustic sensor of LiNbO3 crystal fibers operating at radio frequencies

This study focuses on the growth and characterization of crystalline LiNbO3 (LN) piezoelectric fibers pulled by the Laser Heated Pedestal Growth (LHPG) technique. The electrical properties of the fibers were investigated using an impedance analyzer, which yielded values for resonance frequency, anti-resonance frequency, and phase angle. Subsequently, elastic constants and coupling factor were determined through calculations based on thickness resonance modes. The accuracy of the resonance method was validated through numerical simulations utilizing COMSOL software, demonstrating a close agreement between experimental and simulated results. Additionally, a temperature sensing was conducted, subjecting the fibers to a wide temperature range from 30 °C to 236 °C to assess their sensitivity to temperature variations. The coupling factors of K = 0.37 for LN-1 and K = 0.35 for LN-2 demonstrated efficient performance of the crystalline fibers. Furthermore, the numerical simulations exhibited strong correlation between simulated and experimental data. The sensitivity analysis revealed the potential of LN fibers for temperature sensor applications, exhibiting a sensitivity of −87 Hz.°C−1. These findings underscore the promise of LN piezoelectric fibers in advanced sensing technologies.

High-sensitivity ratiometric thermometers of Yb3+/Er3+/Tm3+ co-doped LuScO3 single crystal fibers based on non-thermally coupled energy levels

Fluorescence thermometry manifests tremendous attention for their potential applications in the temperature sensing, especially for combining wide operating temperature range with high sensitivity. However, the use of thermally coupled energy levels (TCLs) for temperature measurement has strict requirements for energy difference, which limits the sensitivity of detection. In order to satisfy higher sensitivity sensing, the pair of non-thermally coupled energy levels (NTCLs) of 4S3/2 and 3H4 has been innovatively designed. Herein, the sesquioxide Yb,Er,Tm co-doped LuScO3 single crystal fibers (SCFs) had been delicately grown by Laser Heated Pedestal Growth (LHPG) method. The fluorescence intensity ratio (FIR) thermometry was realized based on the Er3+:4S3/2→4I15/2 (545–593 nm) and Tm3+:3H4→3H6 (750–850 nm) NTCLs. Such an obvious FIR-temperature change through the NTCLs presents an outstanding optical thermometric performance, yielding the high temperature sensing with wide range. The maximum value of absolute sensitivity was 2 orders of magnitude higher than the temperature measurement using TCLs. More importantly, the sesquioxide Yb,Er,Tm:LuScO3 SCFs exhibit superior thermal stability that will be helpful to obtain high precision temperature measurement. Hence, our findings might offer some useful inspiration for exploring high-sensitivity luminescent thermometers and enriching the research of temperature measuring materials.

Optical temperature sensing characteristics of Yb3+/Nd3+ co-doped YAG single crystal fiber based on up-conversion luminescence

YAG: 5 mol%Yb3+/x mol%Nd3+(x = 0, 0.5, 1, 2, 4, 7) and YAG: 2 mol%Nd3+ single crystal (SC) fluorescent materials were prepared using laser heated pedestal growth (LHPG) method. The up-conversion (UC) spectra of YAG: Yb3+/Nd3+ were recorded under 980 nm laser excitation, the results show that the optimal material was obtained at 5 mol%Yb3+/2 mol%Nd3+. An integrated YAG single crystal fiber (SCF) with end 5 mol%Yb3+/2 mol%Nd3+ co-doped was prepared by the LHPG method, the temperature-dependent characteristics were measured in the range from 348 K to 1448 K. It shows that the fluorescence intensity increases and then decreases with the increase of temperature. Fluorescence intensity ratios (FIR) in Nd3+ UC spectra, including FIR1 (4F7/2/4F5/2 → 4I9/2), FIR2 (4F9/2/4F5/2 → 4I9/2) and FIR3 (4G5/2/4F9/2 → 4I9/2), vary monotonically in temperature ranges of 348–1273 K, 523–1273 K, and 673–1273 K, respectively. The maximally absolute and relative sensitivities for FIR1 were, respectively, achieved to be 2.34 × 10−3 K−1 at 738 K and 4.61 × 10−1 %K−1 at 390 K, and these values for FIR2 were accordingly achieved to be 1.19 × 10−3 K−1 at 1273 K and 4.59 × 10−1 %K−1 at 735 K, and for FIR3 they were 4.66 × 10−3 K−1 at 1273 K and 4.09 × 10−1 %K−1 at 760 K. Therefore, we believe that the fabricated YAG: Yb3+/Nd3+ fluorescent materials have favorable application potential for optical thermometer.

Directional and lattice engineering growth of sapphire fibers for ultrasonic ultra-high-temperature sensors

High-temperature sensors for extreme environments are in urgent demand with the rapid development of aerospace, nuclear energy, and advanced manufacturing. Ultrasonic temperature sensors (UTS) are widely used in high-temperature sensing due to their high working temperature that approaches the melting point of the acoustic waveguide. Al2O3 single-crystal fiber (SCF), also called sapphire fiber, is a promising candidate for ultrasonic thermometry due to its ultra-high melting point (∼2050 °C), high strength and oxidation resistance. Here, we report for the first time, to the best of our knowledge, large length-diameter ratio sapphire fibers with specific orientations (a-axis, m-axis, and c-axis) have been grown by laser-heated pedestal growth method and applied for ultrasonic temperature sensing. Sapphire fibers exhibit significant acoustic anisotropy, and a-oriented sapphire fiber has a lower acoustic velocity and a greater velocity-temperature variation, leading to higher sensitivity. Moreover, the acoustic velocity of sapphire fiber could be further decreased by doping with Cr ions owing to the enhanced lattice disorder and crystal density. As a result, an improved unit sensitivity of 28.98–52.88 ns°C−1m−1 and a superior resolution of 1.73–0.95 °C have been achieved in the range of 20–1200 °C via a-oriented Cr:Al2O3 SCF-UTS. More importantly, the sensor performance is positively correlated with ambient temperature, accompanied with the high working temperature (∼1800 °C) and excellent stability (∼20 h), demonstrating promising prospects for applications in high-temperature thermometry. This work provides a feasible approach for designing a high-performance UTS based on acoustic anisotropy and lattice engineering.

Selective Laser Spectroscopy of the Bixbyite-Type Yttrium Scandate Doped by Rare-Earth Ions.

Yttrium scandate crystals doped by Nd3+ and Tm3+ ions have been successfully grown in the form of fibers using the laser-heated pedestal growth (LHPG) technique. The selective laser spectroscopy methods have identified and distinguished three distinct types of optically active centers associated with Nd3+ and Tm3+ ions. The substitution of Y3+ and Sc3+ for rare-earth ions in the C2 structural site leads to the formation of two distinct basic long-time centers. In Nd3+:YScO3, another type of center (a short-lifetime one) is formed known as the Nd3+-Nd3+ aggregate pair. This center arises from the substitution of Y3+ or Sc3+ for Nd3+ cation in the adjacent MO6 polyhedra that share an edge. In Tm3+:YScO3, the third optical center is formed as a result of the substitution of Y3+ or Sc3+ for Tm3+ in the MO6 octahedra with the C3i site symmetry. The fluorescence decay lifetimes of Nd3+ and Tm3+ ions in the YScO3 crystal structure have been accurately measured and estimated. A Stark level diagram illustrating the splitting of 4F3/2, 4I11/2, and 4I9/2 multiplets of Nd3+ ions has been constructed to show features of the active optical centers with the C2 site symmetry.

Light response uniformity of LuAG:Ce scintillating single crystal fiber grown by laser heated pedestal growth method

Own to its fine granularity and sub-millimeter position information, scintillating single crystal fibers (SSCFs) hold great potential for various applications such as electromagnetic calorimeters, positron emission tomography, and radiotherapy dosimetry. The light response uniformity of scintillating fibers is an important parameter for precise measurements of ionizing radiation. Three methods were designed to investigate the light response uniformity of the 184-mm-long LuAG:Ce SCCF. Relatively longitudinal-distributed uniformity of cerium element was obtained in this SSCF. The scintillation light attenuation coefficient of the SSCF is 0.27 cm−1 induced by X-ray photons with single-end readout mode and about 0.29 cm−1 induced by gamma rays with dual-end readout mode. The Ce3+ ions self-absorption along the longitudinal light propagation process is one of main reasons for the scintillation light attenuation. Weakening the Ce3+ ions’ self-absorption effect is a possible way to improve the light response uniformity of the LuAG:Ce SSCF.

Growth, spectroscopy properties and laser operation of a novel single crystal fiber: Nd3+-doped CaY0.9Gd0.1AlO4

A Nd3+-doped CaY0.9Gd0.1AlO4 single crystal fiber (Nd: CYGA SCF) with a length of 80 mm and a diameter of 1 mm, to the best of our knowledge, was successfully grown for the first time by a highly efficient laser-heated pedestal growth method. The basic physical and chemical properties, optical properties, and laser properties of the as-grown SCF were studied in detail. The results show that the Nd: CYGA SCF has wider absorption and emission half-peak full width compared with a bulk single crystal. Furthermore, under the pumping of a commercial 808 nm laser diode, a CW laser operation at 1080 nm with a half-height width of 0.29 nm was obtained. The laser output power was 54 mW at an absorbed power of 2.03 W. The slope efficiency was 6.79% with respect to the absorbed pump power. Thus, the Nd: CYGA SCF might be a practical and powerful candidate for laser gain medium, and have a great research space in the field of lasers.

Anisotropic growth and characterizations of large length-diameter ratio sapphire fibers via laser-heated pedestal growth technique

Sapphire fiber is a promising candidate for harsh environment sensing due to its high melting point, compact structure, and corrosion resistance, where the fiber with a smaller diameter and a larger length-diameter ratio is being widely demanded. In this work, high quality sapphire crystal fibers with minimum diameter of 25 μm and maximum length of 24.5 m were successfully prepared by laser-heated pedestal growth technique, which is the dimension record for crystal fibers that ever reported. Sapphire fibers exhibit anisotropic growth behaviors and the c-oriented sapphire fibers were demonstrated to have higher tensile strength compared to a-oriented sapphire fibers, illustrating superior mechanical properties. Moreover, various essential properties such as flexibility, surface roughness, and crystallinity have also been systematically investigated.

Spectral study and energy transfer analysis of Er:YAlO3 crystals

Er:YAP crystals have been proved promising mid-infrared gain materials but there is few systematic study focused on the relationship between the doping concentration and spectral properties. In this work, Er:YAP crystals with a series of doping concentrations(0.1 at.%, 1 at.%, 5 at.%, 10 at.%, 15 at.%, 30 at.%) were fast grown successfully by a modified laser-heated pedestal growth (LHPG) method. Through investigating doping concentration dependent spectral characteristics in detail, we found that the cross relaxation process (Er3+: 4S3/2+4I15/2 → 4I9/2+4I13/2) gets significantly enhanced with the doping concentration when it is below 5 at.%, and eventually tends to saturate. And the cooperative up-conversion process (Er3+: 4I13/2+4I13/2 → 4I15/2+4I9/2) conducive to high-efficiency ∼3 μm laser starts to dominate when the doping concentration is 5 at.% or even less. This result demonstrates the potential of Er:YAP crystals to achieve high-power and high-efficiency laser output under relatively low Er-doping concentration, and offers a valuable guidance for doping optimization of Er:YAP systems.

Growth of a Gradient-Doped Single-Crystal Rod with Designable Distribution of Doped Ions by a Laser-Heated Pedestal Growth Method

Growth of a Gradient-Doped Single-Crystal Rod with Designable Distribution of Doped Ions by a Laser-Heated Pedestal Growth Method

Structural and Spectroscopic Features of the Bixbyite-Type Yttrium Scandate Doped by Rare-Earth Ions

Yttrium scandate crystal fiber has been obtained through laser-heated pedestal growth. The crystal belongs to a bixbyite crystal structure and crystallizes in Ia3¯ space group. X-ray diffraction method shows a lattice parameter of a = 10.228(1) Å. Factor-group analysis of YScO3 Raman spectra points to high degree of disorder in crystal structure of the new compound. Spectral-kinetic investigation of the crystal fibers doped by rare-earth ions points to the presence of two independent active optical centers of rare-earth ions. Moreover, the character of rare-earth impurities’ distribution is independent on a rare-earth ionic radius size.

The growth and properties of Y admixed LuAG:Ce scintillating single crystal fiber fabricated by laser heated pedestal growth method

Aluminum garnet crystal has great potential in detecting the high-energy photons and particles for its good scintillation properties and preparing the high time and spatial resolution fiber-array detector for its' easy preparation as single crystal fiber. 0.2 at% Ce: Lu1-xYxAG (x = 0, 0.25, 0.5, 0.75, 1) scintillating single crystal fibers were successfully prepared by laser heated pedestal growth method. The 5d1 energy level of Ce3+ luminescence center is shifting to lower energy and 5d2 energy level of Ce3+ luminescence center is shifting to higher energy with the Y admixture increasing. The photoluminescence decay was fitted by single-exponential decay curve and the scintillation decay were fitted by double-exponential decay curve instead for the different luminescence mechanism. The highest scintillation light yield of 32,457 Ph/MeV and 10,617 Ph/MeV was obtained from the horizontal-direction and longitudinal-direction sides of 0.2 at% Ce: Lu0.25Y0.75AG scintillating single crystal fiber respectively, demonstrating its perspective for application in High Energy Physics.

Spectroscopy of the yttrium scandate doped by thulium ions

The thulium-doped yttrium scandate crystal fiber has been obtained by the laser-heated pedestal growth method. The crystal belongs to the bixbyite type, has a cubic structure and crystallizes in the Ia3 space group. The lattice parameters (a=10.224(1) Angstrem) have been determined using the powder X-ray diffraction. Spectral-kinetic measurements have allowed to detect two symmetrically independent optical centers of Tm3+ ions in the crystal fiber. Keywords: bixbyite, optical center, rare-earth ion, laser-heated pedestal growth.

Thermal optimization of single crystal fiber manufacturing based on heat loss compensation

Single crystal fiber (SCF) manufacturing, occupying most of the difficulties in the application of next generation high power lasers, has gained significant interest over the years. The thermal optimization of the SCF growth system is imperative to solve the low output laser power and slope efficiency limited by the cracking problem. Using both experimental and simulation approaches that efficiently explore the growth process of sesquioxide crystals in the laser-heated pedestal growth (LHPG) system, the present study explains the reason why the traditional resistance afterheater does not reduce the thermal stress in the SCF from the perspective of the first and second-order derivatives of the temperature field. On the basis, a thermal optimization model based on the idea of thermal compensation is proposed. This form of heat input greatly improves the thermal stress concentration in the crystal and reduces the maximum Von Mises stress by 95%, while perfectly maintaining the uniformity of the overall temperature field. Furthermore, a semi-Gaussian fitting is performed on the optimization model hinting at the possibility of its application in practical engineering. Notably, this thermal compensation idea based on heat loss can be used for reference by other materials and growth systems in the SCF manufacturing field, because heat transfer is always the basis.