Liquid Nitrogen Temperature Research Articles

INFLUENCE OF TEMPERATURE ON THE PROPERTIES OF FREE LOADED INORGANIC OXIDE NANO POWDERS

A comparative study was carried out on the possibility of controlling the average sizes of nano-sized powders of silicon dioxide and aluminum oxide obtained by electron beam evaporation, pyrogenic, liquid chemical and plasma chemical methods, by keeping them in the temperature range of 800 – 1300 ?C in an air atmosphere. The average size of the resulting particles was estimated from specific surface area measurements using the Brunauer–Emmett–Taylor (BET) adsorption method at liquid nitrogen temperature. Crystallographic parameters in the treated powders were assessed using X-ray diffraction analysis. It has been shown that by appropriate choice of temperatures and initial powder, it is possible to achieve an average particle size in the resulting powder close to a given one and a phase composition.

Complex Flow Mechanism and Pressurization Effect of Liquid Nitrogen Jet Fracturing Formation Perforation Tunnel

As an anhydrous fracturing method, liquid nitrogen jet fracturing technology is expected to become an efficient development method for shale gas resources. In order to explore the influence of the pressurization effect in the liquid nitrogen jet channel, the flow field in the perforation tunnel during the liquid nitrogen jet fracturing process was simulated by computational fluid dynamics, and the complex flow mechanism of liquid nitrogen in the perforation tunnel was analyzed. The pressurization effect of liquid nitrogen jet and water jet fracturing was compared, and the influence of various parameters on the pressurization effect of liquid nitrogen jet fracturing was studied. The research results indicate that under the same conditions, liquid nitrogen jets have a pressurization effect comparable to water jets, and the difference between the pressurization values of the liquid nitrogen jet and the water jet in the perforation tunnel is not more than 0.4 MPa under different nozzle pressure drop conditions. The larger the nozzle pressure drop and nozzle diameter, the greater the pressure increase value in the perforation tunnel of liquid nitrogen jet fracturing, which decreases with the increase in casing hole diameter. Further analysis shows that the pressurization effect is most affected by the two parameters of casing hole diameter and nozzle diameter. The essential reason for its influence on the pressurization value is the squeezing effect of the jet on the perforation tunnel fluid and the sealing effect of the shrinking part of the perforation tunnel on the backflow. The ambient pressure, the temperature of liquid nitrogen, and the diameter of the wellbore have no obvious effect on the pressurization effect. Therefore, through the reasonable combination of casing hole diameter and nozzle diameter, the sealing effect of the contraction part of the perforation tunnel on the fluid and the squeezing effect on the fluid in the perforation tunnel will be affected, which will significantly improve the pressurization effect of the liquid nitrogen jet in the perforation tunnel.

Fatigue behaviors and damage mechanisms for Nb3Sn triple-helical structure at liquid nitrogen temperature

Nb3Sn triple-helical structure is the elementary structure in the superconducting cable of ITER magnets and undergoes prolonged fatigue loading in extreme environments leading to serious damage degradation. In this paper, the fatigue behaviors of the Nb3Sn triple-helical structure have been investigated by the strain cycling fatigue experiments at liquid nitrogen temperature. The results indicate that Nb3Sn triple-helical structures with short twist-pitches possess excellent fatigue damage resistance than that of long twist-pitches, such as longer fatigue life, slower damage degradation, and smaller energy dissipation. Meanwhile, a theoretical model of damage evolution has been established to reveal the effects of twist-pitches on fatigue properties for triple-helical structures, which is also validated by the present experimental data. Furthermore, one can see that the Nb3Sn superconducting wires in a triple-helical structure with the shorter twist-pitches have a larger elongation of helical structure and less cyclic deformation, which can be considered as the main mechanism of better fatigue damage properties for the triple-helical structures during the strain cycling processes. These findings provide a better understanding of the fatigue properties and damage mechanisms for Nb3Sn triple-helical structures in superconducting cables of ITER magnets.

Linear magnetoelectric coupling and type-II multiferroic order in NiMn2O4

We report an unexplored type-II multiferroic order in NiMn2O4, exhibiting strong linear magnetoelectric coupling above liquid-nitrogen (LN) temperature. The compound becomes ferroelectric at ∼100 K, coinciding with ferrimagnetic ordering, with a polarization value of ∼535 μC/m2 for a poling field of 5 kV/cm. At LN temperature, the polarization value increases linearly (∼21%) with a magnetic field up to 30 kOe. Rietveld refinement of neutron diffraction patterns reveals a ferrimagnetic model with antiparallel moments at tetrahedral and octahedral sites, as well as a canting of octahedral moment persisting up to ∼100 K. Low-temperature synchrotron diffraction confirms a step-like oxygen displacement during multiferroic ordering, suggesting that the Dzyaloshinskii–Moriya interaction polarizes the intervening oxygen atoms through magnetostriction, providing a microscopic mechanism for spontaneous electric polarization in this linear magnetoelectric multiferroic compound.

Fabrication of YBa2Cu3O7-y Bulk Superconductor Through Melt Growth

A YBa2Cu3O7-y bulk with the crystal orientation identical with that of single seed was grown from the seed by the application of melt growth, wherein YBa2Cu3O7-y superconductive green compact was placed on the upper part of Sm 123 superconductive seed single crystal. Field cooling was employed as the condition for the measuring magnetic levitation; it was measured at the temperature of liquid nitrogen, utilizing a Nd–Fe-B permanent magnet with the force of 3.86 kG. The magnetic levitation measurements yielded values of 23.537 N on the surface of the upper part and 30.562 N at the bottom of superconductive bulk magnet. The trapped magnetic forces on the surfaces of superconducting specimens were measured using a permanent magnet with a surface magnetic force of 5.25 kG. The measurements yielded values of 1.74 kG on the upper surface and 1.82 kG at the bottom of the superconducting bulk magnet. Superconducting single crystals were grown from specimens obtained from the upper and bottom parts of the bulk magnet. These specimens were prepared using the melt reaction process. The superconducting properties, such as magnetic levitation and trapped magnetic force, were found to be higher in the region that came into contact with the seed crystal.

Dislocation behavior and strengthening mechanisms of Cu–Te alloy drawn at room and cryogenic temperatures

In the work, the cryogenic and room temperature drawing behaviors of Cu–Te alloy with a wide range of accumulative drawing true strain up to 1.1 are systematically investigated. For the first time, the storage of geometrically necessary dislocations (GND) and statically stored dislocations (SSD), occurrence of deformation twinning, as well as their respective roles in strain hardening in the drawn Cu–Te alloy at cryogenic and room temperature have been studied. The results show that the liquid nitrogen temperature drawn (LNT-D) Cu–Te alloy presents higher yield strength (YS), ultimate tensile strength than the room temperature drawn (RT-D) Cu–Te alloy. Microstructural investigation reveals that cryogenic wire drawing of Cu–Te alloy promotes the formation of simultaneous twinning and shear bands, accompanied by the fragmentation of Cu2Te phase. The LNT-D Cu–Te alloy exhibits planar slip characteristics, while RT-D Cu–Te alloy presents wave slip characteristics. Compared with RT-D Cu–Te alloy, the higher YS of LNT-D Cu–Te alloy can be mainly attributed to dislocation strengthening and twinning strengthening, which account for 76.25–80.45% and 4.79–4.91% of the total YS respectively. During room temperature drawing, both GND and SSD play an important role in the hardening of Cu–Te alloy. During cryogenic temperature drawing, work hardening is predominantly through rapid multiplication of SSDs.

Few-Hydrogen High-Tc Superconductivity in (Be4)2H Nanosuperlattice with Promising Ductility under Ambient Pressure.

The multi-hydrogen lanthanum hydride LaH10 is well recognized as having the highest critical temperature (Tc) of 250-260 K under unrealistically ultrahigh pressures of about 170-200 GPa. Here, we propose a novel idea for designing a new ambient-pressure high-Tc superconductor by inserting a hexagonal H-monolayer into two close-packed Be monolayers to form a new and stable few-hydrogen metal-bonded layered beryllium hydride (Be4)2H nanosuperlattice, with better ductility than multi-hydrogen, cuprate, and iron-based superconductors, completely contrary to the conventional design strategy for multi-hydrogen covalent high-Tc superconductors with poor ductility at several hundred GPa. We find that (Be4)2H is a phonon-mediated Eliashberg superconductor with a large electron-phonon coupling constant of 1.41 and a high Tc of 84-72 K with Coulomb repulsion pseudopotential μ* = 0.07-0.13. Importantly, (Be4)2H is the only new high-Tc superconductor and fills the gap in the absence of ambient-pressure superconductors around the liquid-nitrogen temperature with good ductility, which is highly beneficial for practical applications.

Superior tensile properties and unique damage-fracture characteristics of Ti-2.5Cu α-titanium alloy at liquid-nitrogen temperature

α-titanium alloys are extensively applied under cryogenic environment and thereby their cryogenic mechanical properties and service failures deserve to be deeply studied. Here, tensile behaviors and damage-fracture characteristics of Ti-2.5Cu α-titanium alloy were systematically investigated at liquid-nitrogen temperature (LT) plus room temperature (RT) for comparison. It is found that the LT samples possess superior strength and ductility concurrently. Both yield strength (σy) and ultimate tensile strength (σb) improve more than 70%, whilst total elongation at fracture (A) adds more than 33% in comparison with the RT counterparts. Meanwhile, the LT samples are stretched mainly by uniform strain without noticeable necking. Fracture analysis indicates that being different from typical cup-and-cone fracture surface in the RT samples, the ‘radial’ fracture surface appears in the LT samples. Such specific fracture surface is constructed by two characteristic morphologies of crack-initiation zone at sample surface and the ensuing crack-propagation zone. Furthermore, it is seen that a large number of micro-voids are dispersed underneath fracture surface in the RT samples, whereas the number of micro-voids is sharply reduced at LT. Nevertheless, Vickers hardness at the position is always much higher in the LT samples. These novel mechanical properties and damage-fracture characteristics in the LT samples are closely associated with the prevalent deformation twinning in microstructure. Deformation twinning itself and plentiful twins-induced dynamic Hall-Petch effect steadily accommodate plastic deformation, contributing to the simultaneous enhancement of strength and ductility. This process also results in high stress state in samples, increasing the sensitivity of surface cracking. Hence, the ‘radial’ fracture morphology is finally formed. These findings enrich our fundamental understanding on deformation-damage-fracture process of α-titanium alloys, and also provide implicit guidance for the design of titanium alloys with high performance.

Extraordinary strength and ductility of cold-rolled 304L stainless steel at cryogenic temperature

In present work, tensile behaviors of cold-rolled 304L stainless steel were investigated at both room temperature (RT) and liquid nitrogen temperature (LNT). After cold-rolling with a thickness reduction of ∼92%, the 304L stainless steel exhibits an ultrahigh yield strength of 1787 MPa at the expense of ductility (1.06% of uniform elongation) at RT. At LNT, the yield strength (upper yield point of σyu = 2308.4 MPa and lower yield point of σyl = 1894.2 MPa) and uniform elongation (23%) increase greatly. Detailed microstructural investigation reveals that the cold-rolled 304L stainless steel comprises mainly of deformation induced martensite and high density of dislocations (9.06 ×1014m−2), leading to a lack of dislocation storage capacity and thus brittle fracture at RT. While interrupt tests at LNT reveal a first increase and then decline in dislocation density with tensile strain, accompanied with phase transformation from austenite to martensite. The delamination events also occur, characterized by the multiple separated laminated ligaments observed at fracture surface. Therefore, the high dense dislocations and transformation-induced plasticity (TRIP) effect as well as delamination toughening mechanism contributes to the excellent combination of strength and ductility at LNT. Our work provides experimental and microstructural insights into the deformation mechanisms of the ∼92%-cold-rolled 304L stainless steel during tensile deformation at RT and LNT.

Critical Current Measurements of HTS Tapes Using Pulsed Current in High Fields at Low Temperatures

High-temperature superconducting (HTS) tapes have been the subject of intensive research for various applications. In addition to their use at high temperatures in liquid nitrogen cooling, they are expected to be utilized in ultra-high field magnets at 30 T or higher at low temperatures, as well as in compact fusion reactors and rotating machines in intermediate temperature ranges. Each company has made significant strides in improving the critical current of HTS tapes, necessitating the development of test facilities with variable temperatures and high currents, such as those of the 2000 A and 20 T class. Typically, a steady current is employed for critical current measurements. In this study, we focus on pulsed current measurements to perform critical current measurements at high currents in limited spaces with high magnetic fields. A probe with a low inductance was fabricated, and a trapezoidal pulse current of 2-10 ms was applied to the sample using a 500 A-class pulse power supply. The current and voltage of the sample were recorded using a high-resolution isolated oscilloscope. By integrating this system with a 20 T cryogen-free superconducting magnet and a He-flow cryostat, critical currents in commercially available HTS tapes with 4 mm width were measured at temperatures ranging from 4 K to 77 K and magnetic fields up to 19 T. The Lorentz force caused the probe to oscillate and the voltage leads to swing, resulting in substantial voltage noise. Noise reduction down to 0.6 μV was achieved under 19 T, 500 A conditions, by fixing the voltage leads and changing the direction of Lorentz forces on the probe. The field dependences of the critical currents in a HTS REBCO tape characterized with pulsed and steady-state currents were compared and determined to be equivalent.

Flux Noise Reduction of HTS-SQUIDs via Introduction of Antidots

High- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> superconducting quantum interference devices (HTS-SQUID), which can be used at near liquid nitrogen temperature, allow for reduction of the SQUID equipment both size and operating costs. However, the noise of HTS-SQUID, which consists of white and 1/f noise is higher than that of low- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> SQUID. The 1/f noise, particularly prominent in HTS devices, is generated by fluctuations of the critical current in the Josephson junction and by the motion of the magnetic flux trapped in the superconducting thin film. Presence of low-frequency noise is a problem especially in HTS-SQUID applications such as bioinstrumentation, environmental measurement, and magnetic contamination inspection. Nanoscale holes (antidots) in HTS films are known to attract and pin magnetic flux. In this study, we investigate the effect of artificially introduced nanoscale antidots near the junction boundaries on the noise characteristics of bicrystal SQUIDs. We used focused ion beam irradiation to create in YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-</sub> <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">_δ</i> (YBCO) thin film holes of about 90 nm in diameter. As a result of the antidots introduction, the 1/f noise of the bicrystal SQUID in a magnetic field of 66 μT at 77 K was significantly reduced.

Optimization of the Direct Diffusion Bonding Process Using Cu Stabilizing Layers of the REBCO Coated Conductors

Low resistivity joint technique for high-temperature superconducting tapes is one of the most indispensable techniques for practical applications. In the present study, we propose solid phase joining technique to make direct joint of REBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> (REBCO, RE:rare earth elements) tapes, as an alternative to conventional solder joining technique. In this solid phase joining technique, we directly join the copper stabilizing layer and get rid of the soldering material, so that we can expect reduction of joint resistivity. The important points for direct joining technique are to remove the oxide layer on the metal surface and to make the joint surface adhere to each other. It means that, after removing the oxide film on the surface, it is necessary to have an optimum pressure so that sufficient adhesion can be obtained while maintaining a clean surface. First, we examined the type and concentration of the acid used to remove the oxide film. Next, the joining pressure, joining atmosphere, and joining time were optimized, while the joining temperature was fixed at 200°C. Finally, we have succeeded in joining REBCO tape with this technique. The measured resistivity at liquid nitrogen temperature was about 50-80 nΩcm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Basic Research on a Magnetic Refrigeration System for Cooling to Liquid Hydrogen Temperature

Magnetic refrigeration technology is expected to be a highly efficient process at a temperature of around 20 K, which is the hydrogen liquefaction temperature. In magnetic refrigeration, a magnetic field change is applied to a magnetocaloric material (MCM) to obtain a magnetocaloric effect. In addition, since the greater the magnetic field change, the better the cooling characteristics, the magnetic field strength of permanent magnets is insufficient, and the use of superconducting coils that can generate strong magnetic fields with low power consumption is essential. We are researching and developing a static magnetic refrigeration system (SMRS) that does not have moving parts to obtain magnetic field changes, and generates them by altering the energizing current to the coil. The key to devising this system is an AC loss of the superconducting coil. In this study, we measured the AC loss under energization conditions of multiple palm-sized REBCO coils at liquid nitrogen temperature, and calculated the efficiency of the SMRS by improving the accuracy of the analysis method for evaluating the AC loss, based on the results. We report the results and discuss the technical feasibility of SMRS.

Screening Study of Different Carbon-Based Materials for Hydrogen Storage

In this study, the hydrogen uptake of five carbon-based materials; graphite flakes (GF), graphene oxide (GO), graphene, multi-walled carbon nanotubes (MWCNT), activated carbon, mesoporous carbon and carbon microspheres (CMS) was explored. The characteristic techniques used to confirm the materials included Powder X-ray Diffraction (PXRD), Attenuated Total Reflection (ATR) Fourier transform infrared (FTIR) spectroscopy, Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM). Nitrogen adsorption isotherms, BET surface area and pore size distributions were measured at liquid nitrogen temperature (77 K). The hydrogen storage capacity was studied at constant temperature, 77 K and pressure from ambient pressure up to 1 bar. This study found that mesoporous carbon had the highest percentage of hydrogen uptake (18%), while activated carbon had the lowest percentage of hydrogen uptake (2%).

High-Tc Josephson Junction Arrays for THz Applications

High-T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> superconductors (HTS) like yttrium barium copper oxide (YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-x</sub> ) pave the way towards readily available and precise voltage standards at liquid nitrogen temperatures. They can be driven by terahertz radiation, thus achieving higher output voltages with a significantly reduced junction count. The reduced effort in cooling also simplifies the overall application. The use of a gallium focused ion beam (Ga-FIB) represents a promising method to tailor the geometry of Josephson junctions after conventional patterning of an array to tune the junction parameters individually. In this work, we present a Josephson junction array made from the HTS YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-x</sub> based on grain-boundary Josephson junctions. The junction parameters are investigated and afterwards the influence of the Ga-FIB on the junctions is examined. This serves as an important step to show the suitability of this process for HTS voltage standards. Furthermore, the high frequency properties of the array and the associated Shapiro steps are characterized in the terahertz range. This technique represents an important step towards versatile HTS voltage standards.

HTS Dipole Magnet With Mechanical Energy Transfer in the Magnetic Field

Several high-temperature superconducting (HTS) model magnets for particle accelerators were designed and successfully tested at Fermilab. Some worked in a persistent current mode by continuously generating magnetic fields in the iron-dominated magnet gap. This paper investigated a novel HTS dipole magnet concept with a mechanical energy transfer in the magnetic field. To pump the energy in the superconducting HTS dipole magnet, a detachable magnetizer was used. The HTS dipole magnet was built and successfully tested at a liquid nitrogen temperature. We discuss the magnet design, test results, the proposed approach limits, and efficiency.

Numerical and Experimental Design of the Former for TORT Cables

TORT (Tapes on Round Tube) cables, which implement high-temperature superconducting (HTS) tapes, offer additional benefit over other HTS cables, which is the internal cooling in the former itself. Up to now, the superconducting tapes of existing TORT cables have been wound on a copper tube of various diameters. However, in the alternating current (AC) mode, the high conductivity of the former causes undesirable eddy currents. Therefore, it is necessary to replace the copper with a less electrically conductive material. We designed a former from polyethylene terephthalate glycol-modified and reinforced with carbon fibers (PETG CF), polycarbonate (PC) and polycarbonate reinforced with carbon fibers (PC CF) materials in order to reduce the AC losses in TORT cables, using 3D printing technology. Because of the low thermal conductivity of polymers, the former must be specially designed to improve the cooling of the HTS tapes inside the former. Moreover, thermal deformation of the former during cooling from room temperature to liquid nitrogen temperature and resilience against low-diameter bending is another important issue that was taken into account. Detailed structural finite-element (FE) analysis was carried out using the FE modeling software ANSYS, in prototyping of the former. Based on the numerical models, formers differing in the materials used were fabricated, and subsequently a short TORT cable with wound HTS tape was electromagnetically characterized.

Current Sharing Among Transposed Three-Parallel REBa2Cu3O y Tapes in Single-Phase Armature Coils

To realize a large current capacity in REBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">_y</i> superconducting coils, we have proposed a cabling design for the transposed multi-strand parallel conductors. This cabling design is also useful for a superconducting armature coil in a fully superconducting rotating machine system. Very recently, we developed an analytical method based on simple modeling, to roughly calculate the current distributions among the continuous strands in rotating machine conditions. In this manuscript, the current distributions predicted by the analytical method were compared with the measured values. Further, to understand the complex current distribution property for the three-strand parallel conductors, the turn number dependence of the current distribution with various transposition combinations was investigated. The current branches were measured under liquid nitrogen temperature of 77.3 K by Rogowski coils by applying AC transport current. The analytical method described the complex current distribution of the strands well, especially the coil with a large number of turns.

Spectral and temporal properties of 5-phenyl-2-[4-(5-phenyl-1,3-oxazol-2-yl)phenyl]-1,3-oxazole (POPOP) multiphoton-excited luminescence

The results of a study of multiphoton-excited luminescence and Stimulated Raman scattering (SRS) of POPOP in a form of crystalline powder and toluene solution are presented. Two-photon and three-photon-excited luminescence in POPOP crystalline powder and toluene solution was registered under excitation by pico- and nanosecond laser pulses. Samples cooling to the temperature of liquid nitrogen leads to the appearance of an additional line in the luminescence spectrum at a wavelength of 447 nm, SRS lines intensity increasing accompanying two-photon luminescence process and changing temporal dynamics, a decrease in the contribution of the fast component in the decay time curve.

Study of Fe:ZnSe Laser Exited by Diode Side-Pumped Er:YAG Laser

The performance of a Fe:ZnSe laser was investigated in different schemes of excitation by a pulsed diode side-pumped Er:YAG laser. At the temperature of liquid nitrogen, the Fe:ZnSe laser, pumped by a free running 360-μs Er:YAG laser and demonstrated a pulse energy of 53 mJ with a slope efficiency of 42% relative to absorbed pump energy. When operating at room temperature, two optical schemes were considered. In the first one, the Fe:ZnSe laser crystal was pumped by a Q-switched Er:YAG laser with a passive shutter based on an additional Fe:ZnSe crystalline plate, and the cavities of both lasers were independent. In the second scheme, the cavities of the Fe:ZnSe and Er:YAG lasers were coupled, and the Fe:ZnSe crystal simultaneously served as an active element of the Fe:ZnSe laser and a passive shutter of the Er:YAG laser. Pulses with a duration of less than 200 ns and an energy of ~1 mJ were obtained from the Fe:ZnSe laser with a repetition rate of up to 50 kHz. The experimental waveforms of the laser pulses were approximated by rate equations.