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New laser materials for laser diode pumping

The potential advantages of laser diode pumped solid state lasers are many with high overall efficiency being the most important. In order to realize these advantages, the solid state laser material needs to be optimized for diode laser pumping and for the particular application. In the case of the Nd laser, materials with a longer upper level radiative lifetime are desirable. This is because the laser diode is fundamentally a cw source, and to obtain high energy storage, a long integration time is necessary. Fluoride crystals are investigated as host materials for the Nd laser and also for IR laser transitions in other rare earths, such as the 2 micron Ho laser and the 3 micron Er laser. The approach is to investigate both known crystals, such as BaY2F8, as well as new crystals such as NaYF8. Emphasis is on the growth and spectroscopy of BaY2F8. These two efforts are parallel efforts. The growth effort is aimed at establishing conditions for obtaining large, high quality boules for laser samples. This requires numerous experimental growth runs; however, from these runs, samples suitable for spectroscopy become available.

Jenssen, H. P.↗

Materials Data on MnP(HO)7 by Materials Project

MnP(HO)7 crystallizes in the orthorhombic Pbca space group. The structure is three-dimensional. Mn2+ is bonded to six O2- atoms to form MnO6 octahedra that share corners with three equivalent PO4 tetrahedra. There are a spread of Mn–O bond distances ranging from 2.14–2.27 Å. P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with three equivalent MnO6 octahedra. The corner-sharing octahedra tilt angles range from 22–50°. There are a spread of P–O bond distances ranging from 1.51–1.61 Å. There are seven inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 1.00 Å. In the second H1+ site, H1+ is bonded in a linear geometry to two O2- atoms. There is one shorter (1.02 Å) and one longer (1.61 Å) H–O bond length. In the third H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the fourth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the fifth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. In the sixth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the seventh H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. There are seven inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one P5+ and one H1+ atom. In the second O2- site, O2- is bonded in a bent 150 degrees geometry to one Mn2+ and one P5+ atom. In the third O2- site, O2- is bonded in a distorted water-like geometry to one Mn2+ and two H1+ atoms. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to one Mn2+, one P5+, and one H1+ atom. In the fifth O2- site, O2- is bonded in a distorted water-like geometry to one Mn2+ and two H1+ atoms. In the sixth O2- site, O2- is bonded in a 1-coordinate geometry to one Mn2+ and one P5+ atom. In the seventh O2- site, O2- is bonded in a distorted water-like geometry to one Mn2+ and two H1+ atoms.

36 MATERIALS SCIENCE↗

Quantification of Key Peroxy and Hydroperoxide Intermediates in the Low-Temperature Oxidation of Dimethyl Ether

Dimethyl ether (DME) oxidation is a model chemical system with a small number of prototypical reaction intermediates that also has practical importance for low-carbon transportation. Although it has been studied experimentally and theoretically, ambiguity remains in the relative importance of competing DME oxidation pathways in the low-temperature autoignition regime. To focus on the primary reactions in DME autoignition, we measured the time-resolved concentration of five intermediates, CH 3 OCH 2 OO (ROO), OOCH 2 OCH 2 OOH (OOQOOH), HOOCH 2 OCHO (hydroperoxymethyl formate, HPMF), CH 2 O, and CH 3 OCHO (methyl formate, MF), from photolytically initiated experiments. We performed these studies at P = 10 bar and T = 450-575 K, using a high-pressure photolysis reactor coupled to a time-of-flight mass spectrometer with tunable vacuum-ultraviolet synchrotron ionization at the Advanced Light Source. Our measurements reveal that the timescale of ROO decay and product formation is much shorter than predicted by current DME combustion models. The models also strongly underpredict the observed yields of CH 2 O and MF and do not capture the temperature dependence of OOQOOH and HPMF yields. Adding the ROO + OH $\rightarrow$ RO + HO 2 reaction to the chemical mechanism (with a rate coefficient approximated from similar reactions) improves the prediction of MF. Increasing the rate coefficients of ROO ↔ QOOH and QOOH + O 2 ↔ OOQOOH reactions brings the model predictions closer to experimental observations for OOQOOH and HPMF, while increasing the rate coefficient for the QOOH $\rightarrow$ 2 CH 2 O + OH reaction is needed to improve the predictions of formaldehyde. In conclusion, to aid future quantification of DME oxidation intermediates by photoionization mass spectrometry, we report experimentally determined ionization cross-sections for ROO, OOQOOH, and HPMF.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Machine Learning-Guided Discovery of Ternary Compounds Containing La, P, and Group 14 Elements

In this work, we integrate a deep machine learning (ML) method with first-principles calculations to efficiently search for the energetically favorable ternary compounds. Using La–Si–P as a prototype system, we demonstrate that ML-guided first-principles calculations can efficiently explore crystal structures and their relative energetic stabilities, thus greatly accelerate the pace of material discovery. A number of new La–Si–P ternary compounds with formation energies less than 30 meV/atom above the known ternary convex hull are discovered. Among them, the formation energies of La 5 SiP 3 and La 2 SiP phases are only 2 and 10 meV/atom, respectively, above the convex hull. These two compounds are dynamically stable with no imaginary phonon modes. Moreover, by replacing Si with heavier-group 14 elements in the eight lowest-energy La–Si–P structures from our ML-guided predictions, a number of low-energy La–X–P phases (X = Ge, Sn, Pb) are predicted.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Unsteady aerodynamic flow field analysis of the space shuttle configuration. Part 2: Launch vehicle aeroelastic analysis

An exploratory analysis has been made of the aeroelastic stability of the Space Shuttle Launch Configuration, with the objective of defining critical flow phenomena with adverse aeroelastic effects and developing simple analytic means of describing the time-dependent flow-interference effects so that they can be incorporated into a computer program to predict the aeroelastic stability of all free-free modes of the shuttle launch configuration. Three critical flow phenomana have been identified: (1) discontinuous jump of orbiter wing shock, (2) inlet flow between orbiter and booster, and (3) H.O. tank base flow. All involve highly nonlinear and often discontinuous aerodynamics which cause limit cycle oscillations of certain critical modes. Given the appropriate static data, the dynamic effects of the wing shock jump and the HO tank bulbous base effect can be analyzed using the developed quasi-steady techniques. However, further analytic and experimental efforts are required before the dynamic effects of the inlet flow phenomenon can be predicted for the shuttle launch configuration.

Reding, J. P.↗

Oscillator strengths for S I, S II, and S III

A series of calculations for atomic data of various sulfur and oxygen ions is examined. Recent observations of the Io plasma torus obtained with the Voyager UV Spectrometer, the IUE satellite short wavelength spectrograph, and the rocket-borne faint object telescope are discussed. The calculation of oscillator strengths for S II, the P I sequence, S I, and S III in terms of configuration interaction effects is described. The derivation of orbital wave functions is considered. The use of the close coupling method to estimate collision strengths is studied. The accuracy of these calculations depends on: (1) the number of states used in the close coupling expansion; (2) resonance contributions to the thermally averaged collision strength; and (3) the quality of the target state wave functions. Tables of the derived oscillator strengths are presented.

Ho, Y. K.↗

Materials Data on Ho20In40Rh19 by Materials Project

Ho20Rh19In40 crystallizes in the tetragonal P-4m2 space group. The structure is three-dimensional. there are five inequivalent Ho sites. In the first Ho site, Ho is bonded in a 4-coordinate geometry to four equivalent Rh and eight In atoms. All Ho–Rh bond lengths are 3.00 Å. There are four shorter (3.28 Å) and four longer (3.46 Å) Ho–In bond lengths. In the second Ho site, Ho is bonded in a 4-coordinate geometry to four Rh and eight In atoms. There are two shorter (3.02 Å) and two longer (3.05 Å) Ho–Rh bond lengths. There are two shorter (3.34 Å) and six longer (3.35 Å) Ho–In bond lengths. In the third Ho site, Ho is bonded in a 3-coordinate geometry to four Rh and ten In atoms. There are a spread of Ho–Rh bond distances ranging from 3.06–3.58 Å. There are a spread of Ho–In bond distances ranging from 3.18–3.73 Å. In the fourth Ho site, Ho is bonded in a 2-coordinate geometry to two equivalent Rh and five In atoms. Both Ho–Rh bond lengths are 2.90 Å. There are a spread of Ho–In bond distances ranging from 3.11–3.40 Å. In the fifth Ho site, Ho is bonded in a 2-coordinate geometry to two equivalent Rh and seven In atoms. Both Ho–Rh bond lengths are 2.93 Å. There are a spread of Ho–In bond distances ranging from 3.11–3.44 Å. There are six inequivalent Rh sites. In the first Rh site, Rh is bonded in a 9-coordinate geometry to five Ho and five In atoms. There are a spread of Rh–In bond distances ranging from 2.82–2.86 Å. In the second Rh site, Rh is bonded in a 10-coordinate geometry to three Ho and six In atoms. There are a spread of Rh–In bond distances ranging from 2.73–2.98 Å. In the third Rh site, Rh is bonded in a 8-coordinate geometry to eight In atoms. There are four shorter (2.72 Å) and four longer (2.88 Å) Rh–In bond lengths. In the fourth Rh site, Rh is bonded in a 8-coordinate geometry to eight In atoms. There are four shorter (2.74 Å) and four longer (2.88 Å) Rh–In bond lengths. In the fifth Rh site, Rh is bonded in a distorted hexagonal bipyramidal geometry to eight In atoms. There are four shorter (2.69 Å) and four longer (2.89 Å) Rh–In bond lengths. In the sixth Rh site, Rh is bonded in a 10-coordinate geometry to three Ho and six In atoms. There are a spread of Rh–In bond distances ranging from 2.73–2.97 Å. There are nine inequivalent In sites. In the first In site, In is bonded in a 2-coordinate geometry to two equivalent Ho, two Rh, and one In atom. The In–In bond length is 3.23 Å. In the second In site, In is bonded in a 3-coordinate geometry to two equivalent Ho, three Rh, and one In atom. The In–In bond length is 3.22 Å. In the third In site, In is bonded in a 3-coordinate geometry to four Ho and three Rh atoms. In the fourth In site, In is bonded in a 2-coordinate geometry to two equivalent Ho and two equivalent Rh atoms. In the fifth In site, In is bonded in a 11-coordinate geometry to four Ho, three Rh, and two equivalent In atoms. Both In–In bond lengths are 3.31 Å. In the sixth In site, In is bonded in a 3-coordinate geometry to six Ho and three Rh atoms. In the seventh In site, In is bonded in a 11-coordinate geometry to four Ho, three Rh, and two equivalent In atoms. Both In–In bond lengths are 3.31 Å. In the eighth In site, In is bonded in a 2-coordinate geometry to five Ho, three Rh, and five In atoms. Both In–In bond lengths are 3.25 Å. In the ninth In site, In is bonded in a 7-coordinate geometry to five Ho, three Rh, and five In atoms.

36 MATERIALS SCIENCE↗

Axion optical induction of antiferromagnetic order

Using circularly polarized light to control quantum matter is a highly intriguing topic in physics, chemistry and biology. Previous studies have demonstrated helicity-dependent optical control of chirality and magnetization, with important implications in asymmetric synthesis in chemistry; homochirality in biomolecules; and ferromagnetic spintronics. We report the surprising observation of helicity-dependent optical control of fully compensated antiferromagnetic order in two-dimensional even-layered MnBi 2 Te 4 , a topological axion insulator with neither chirality nor magnetization. Furthermore, to understand this control, we study an antiferromagnetic circular dichroism, which appears only in reflection but is absent in transmission. We show that the optical control and circular dichroism both arise from the optical axion electrodynamics. Our axion induction provides the possibility to optically control a family of PT-symmetric antiferromagnets (P, inversion; T, time-reversal) such as Cr 2 O 3 , even-layered CrI3 and possibly the pseudo-gap state in cuprates. In MnBi 2 Te 4 , this further opens the door for optical writing of a dissipationless circuit formed by topological edge states.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Simultaneous, in situ measurements of OH, HO2, O3, and H2O - A test of modeled stratospheric HO(x) chemistry

Simultaneous, in situ measurements of OH, HO2, H2O, and O3 from 37-23 km are reported. The partitioning between OH and HO2 and the total HO(x) concentration are compared with expected steady-state values. The ratio of HO2 to OH varies from less than 2 at 36 km to more than 3 at 25 km; in the lower stratosphere this ratio is nearly a factor of two less than predicted. The data are used to calculate HO(x) production and loss rates. The measured HO(x) mixing ratio is consistent with production dominated by the reaction of O(1D) with H2O, and loss controlled by NOy below 28 km and HO(x) above 30 km. The steady-state concentration of H2O2 is inferred from the measured HO2 concentration and calculated photolysis rate. The maximum H2O2 mixing ratio (at 33 km) is predicted to be less than 0.2 ppb.

Wennberg, P. O.↗

Aircraft NO/x/ emissions and stratospheric ozone reductions - Another look

New estimates for stratospheric ozone perturbations attributable to supersonic transport (SST) emissions are presented. First, a review is given of recent data pointing to lower OH concentrations below 30 km, as compared to the values predicted by photochemical models. The evidence for lower OH comes from a wide range of laboratory and atmospheric studies. The sensitivity of theoretical estimates of ozone change to OH abundances, and the coupling mechanisms between the O(x)-NO(x)-HO(x)-Cl(x) families which are responsible for the sensitivity, are discussed. Updated calculations for SST-induced ozone alterations are compared with older predictions. For example, assuming continuous aircraft injection of NO2 at 20 km at a rate of 1 x 10 to the 9th kg per year (globally), a 4% ozone decrease, is now calculated where earlier a 3% ozone increase was found. This large variance from previous forecasts suggests that new assessments of certain other polluting agents, particularly nitrogen fertilizers, are needed.

Turco, R. P.↗

Ho:Tm:Lu(3)Al(5)O(12) As An Infrared-Laser Material

Material selected on basis of quantum-mechanical modeling of lasing properties. Ho:Tm:Lu(3)Al(5)O(12) features relatively low thermal occupation of lower laser level because this level higher than corresponding levels of most other available laser materials. In addition, it has reasonably large effective cross section for stimulated emission because of contribution of several transitions around central strong transition. Yet another desirable property is its calculated rate of upconversion is lower than those of other laser materials. Inasmuch as upconversion detracts from efficiency of laser, this lower rate of upconversion is highly desirable.

Barnes, Norman P.↗

Materials Data on Na3Ho(PO4)2 by Materials Project

Na3Ho(PO4)2 crystallizes in the orthorhombic Pca2_1 space group. The structure is three-dimensional. there are six inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Na–O bond distances ranging from 2.35–2.92 Å. In the second Na1+ site, Na1+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Na–O bond distances ranging from 2.29–2.91 Å. In the third Na1+ site, Na1+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Na–O bond distances ranging from 2.31–2.57 Å. In the fourth Na1+ site, Na1+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Na–O bond distances ranging from 2.29–2.87 Å. In the fifth Na1+ site, Na1+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Na–O bond distances ranging from 2.35–2.95 Å. In the sixth Na1+ site, Na1+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Na–O bond distances ranging from 2.31–2.60 Å. There are two inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ho–O bond distances ranging from 2.25–2.53 Å. In the second Ho3+ site, Ho3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ho–O bond distances ranging from 2.26–2.53 Å. There are four inequivalent P5+ sites. In the first P5+ site, P5+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of P–O bond distances ranging from 1.54–1.57 Å. In the second P5+ site, P5+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of P–O bond distances ranging from 1.54–1.57 Å. In the third P5+ site, P5+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of P–O bond distances ranging from 1.54–1.56 Å. In the fourth P5+ site, P5+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of P–O bond distances ranging from 1.54–1.57 Å. There are sixteen inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to three Na1+ and one P5+ atom. In the second O2- site, O2- is bonded in a distorted single-bond geometry to four Na1+, one Ho3+, and one P5+ atom. In the third O2- site, O2- is bonded in a 1-coordinate geometry to two Na1+, one Ho3+, and one P5+ atom. In the fourth O2- site, O2- is bonded in a 1-coordinate geometry to four Na1+, one Ho3+, and one P5+ atom. In the fifth O2- site, O2- is bonded in a 4-coordinate geometry to two Na1+, one Ho3+, and one P5+ atom. In the sixth O2- site, O2- is bonded in a 4-coordinate geometry to three Na1+ and one P5+ atom. In the seventh O2- site, O2- is bonded in a 1-coordinate geometry to three Na1+, one Ho3+, and one P5+ atom. In the eighth O2- site, O2- is bonded in a 3-coordinate geometry to one Na1+, one Ho3+, and one P5+ atom. In the ninth O2- site, O2- is bonded in a 1-coordinate geometry to one Na1+, one Ho3+, and one P5+ atom. In the tenth O2- site, O2- is bonded in a 1-coordinate geometry to one Na1+, one Ho3+, and one P5+ atom. In the eleventh O2- site, O2- is bonded in a 4-coordinate geometry to two Na1+, one Ho3+, and one P5+ atom. In the twelfth O2- site, O2- is bonded in a 1-coordinate geometry to three Na1+, one Ho3+, and one P5+ atom. In the thirteenth O2- site, O2- is bonded in a 1-coordinate geometry to three Na1+, one Ho3+, and one P5+ atom. In the fourteenth O2- site, O2- is bonded in a 1-coordinate geometry to three Na1+, one Ho3+, and one P5+ atom. In the fifteenth O2- site, O2- is bonded in a 1-coordinate geometry to three Na1+, one Ho3+, and one P5+ atom. In the sixteenth O2- site, O2- is bonded in a 1-coordinate geometry to three Na1+, one Ho3+, and one P5+ atom.

36 MATERIALS SCIENCE↗

Complex-coordinate calculation of (1,3)P resonances in Ps(-) using Hylleraas functions

An accurate calculation for (1,3)P autodetaching resonances in Ps(-) has been carried out using the complex-rotation method, which has the advantage of giving resonance position and width at the same time. The wave function is of the Hylleraas type with an available number of terms up to 1140. One 1P and two 3P resonances below the n = 2 threshold and two 1P and two 3P resonances below the n = 3 threshold of the positronium atom. Resonance parameters are compared with those obtained from scattering and adiabatic calculations where available.

Bhatia, A. K.↗

A High Energy 2-microns Laser for Multiple Lidar Applications

Solid-state 2-microns laser has been receiving considerable interest because of its eye-safe property and efficient diode pump operation, It has potential for multiple lidar applications to detect water vapor. carbon dioxide and winds. In this paper, we describe a 2-microns double pulsed Ho:Tm:YLF laser and end-pumped amplifier system. A comprehensive theoretical model has been developed to aid the design and optimization of the laser performance. In a single Q-switched pulse operation the residual energy stored in the Tm atoms will be wasted. However, in a double pulses operation mode, the residual energy stored in the Tm atoms will repopulate the Ho atoms that were depleted by the extraction of the first Q-switched pulse. Thus. the Tin sensitized Ho:YLF laser provides a unique advantage in applications that require double pulse operation, such as Differential Absorption Lidar (DIAL). A total output energy of 146 mJ per pulse pair under Q-switch operation is achieved with as high as 4.8% optical to optical efficiency. Compared to a single pulse laser, 70% higher laser efficiency is realized. To obtain high energy while maintaining the high beam quality, a master-oscillator-power-amplifier 2-microns system is designed. We developed an end-pumped Ho:Tm:YLF disk amplifier. This amplifier uses two diode arrays as pump source. A non-imaging lens duct is used to couple the radiation from the laser diode arrays to the laser disk. Preliminary result shows that the efficiency of this laser can be as high as 3%, a factor of three increases over side-pump configuration. This high energy, highly efficient and high beam quality laser is a promising candidate for use in an efficient, multiple lidar applications.

Yu, Jirong↗

Dense gas and HII regions in the starburst galaxy NGC 253

The energetic activity in the nuclear barred region of NGC 253 is attributable to a burst of star formation. NGC 253 is in many ways a twin of the prototypical starburst galaxy M82; the strong non-thermal radio continuum, high far-infrared luminosity, and bright molecular emission of the central 1 Kpc parallel the morphology of the M82 starburst. Furthermore, the filamentary low ionization optical emission and extended x ray emission along the minor axis in NGC 253 is similar to a scaled down version of the well developed galactic bipolar wind in M82. The infrared luminosity of NGC 253, 3(exp 10) solar luminosity, is comparable to M82 but is emitted from a smaller region (Telesco and Harper 1980). This suggests that the NGC 253 starburst may be more intense and at an earlier evolutionary stage than M82. However, the presence of a non-stellar AGN in NGC 253 may complicate the comparison (Turner and Ho, 1985). Researchers used the Hat Creek millimeter interferometer to map emission from the J = 1 to 0 transitions of HCN and HCO(+) as well as 3 mm continuum emission, toward the nuclear region of NGC 253. The HCO(+) and continuum observations are sensitive to spatial scales from 6 to 45 seconds. The 2 minute field of view comfortably includes the entire starburst region (about 40 seconds; 650 pc). Because the longer baseline HCN observations are not yet complete, they are only sensitive to spatial scales from 15 to 45 seconds.

Carlstrom, J. E.↗

Improved Pyrotechnic Shock Scaling Method Based on Shock Response Spectrum and Statistical Energy Analysis

It has been more than forty years since the pyrotechnic shock scaling method was introduced. The scaling method estimates the attenuation of the Shock Response Spectrum (SRS) based on the distance from the source, structural configurations, types of structural joints and interfaces, and intervening structure [1]. The method has been successfully used in the spacecraft community countless times and still is frequently used to develop pyrotechnic shock requirements at various levels of assembly of a spacecraft. However, since the method was derived empirically from a limited set of shock test data [2], the aerospace community has been looking for an alternative approach. In this paper, a computational scaling method based on Statistical Energy Analysis (SEA) is re-visited. SEA is traditionally used as a method for investigating the diffusion of acoustic and vibratory energies of a system at steady-state [3]. Previously, an approach using the SRS as an acceleration constraint condition to the SEA model was introduced to estimate the attenuation from a shock source [4,5]. In the current investigation, additional examples are provided to further validate the approach. In addition, responses in the time domain are produced by the Local Modal Phase Reconstruction (LMPR) approach which was recently introduced to the community [6].

Fernandez, Juan P.↗

Initial Characterization of Active Transitioning Centaur, P/2019 LD{sub 2} (ATLAS), Using Hubble, Spitzer, ZTF, Keck, Apache Point Observatory, and GROWTH Visible and Infrared Imaging and Spectroscopy

We present visible and mid-infrared imagery and photometry of temporary Jovian co-orbital comet P/2019 LD{sub 2} taken with Hubble Space Telescope/Wide Field Camera 3 (HST/WFC3), Spitzer Space Telescope/Infrared Array Camera (Spitzer/IRAC), and the GROWTH telescope network, visible spectroscopy from Keck/Low-Resolution Imaging Spectrometer (LRIS), and archival Zwicky Transient Facility observations taken between 2019 April and 2020 August. Our observations indicate that the nucleus of LD{sub 2} has a radius between 0.2 and 1.8 km assuming a 0.08 albedo and a coma dominated by ∼100 μm-scale dust ejected at ∼1 m s{sup −1} speeds with a ∼1′ jet pointing in the southwest direction. LD{sub 2} experienced a total dust mass loss of ∼10{sup 8} kg at a loss rate of ∼6 kg s{sup −1} with Afρ/cross section varying between ∼85 cm/125 km{sup 2} and ∼200 cm/310 km{sup 2} from 2019 April 9 to 2019 November 8. If the increase in Afρ/cross section remained constant, it implies LD{sub 2}'s activity began ∼2018 November when within 4.8 au of the Sun, implying the onset of H{sub 2}O sublimation. We measure CO/CO{sub 2} gas production of ≲10{sup 27} mol s{sup −1}/≲10{sup 26} mol s{sup −1} from our 4.5 μm Spitzer observations; g–r = 0.59 ± 0.03, r–i = 0.18 ± 0.05, and i–z = 0.01 ± 0.07 from GROWTH observations; and H{sub 2}O gas production of ≲80 kg s{sup −1} scaling from our estimated C {sub 2} production of Q{sub C{sub 2}}≲7.5×10{sup 24} mol s{sup −1} from Keck/LRIS spectroscopy. We determine that the long-term orbit of LD{sub 2} is similar to Jupiter-family comets having close encounters with Jupiter within ∼0.5 Hill radius in the last ∼3 y and within 0.8 Hill radius in ∼9 y. Additionally, 78.8% of our orbital clones are ejected from the solar system within 1 × 10{sup 6} yr, having a dynamical half-life of 3.4 × 10{sup 5} yr.

47 OTHER INSTRUMENTATION↗

High Efficiency End-Pumped Ho:Tm:YLF Disk Amplifier

Space based coherent lidar for global wind measurement requires an all solid state laser system with high energy, high efficiency and narrow linewidth that operates in the eye safe region. A Q-switched, diode pumped Ho:Tm:YLF 2 micrometer laser with output energy of as much as 125 mJ at 6 Hz with an optical-to-optical efficiency of 3% has been reported. Single frequency operation of the laser was achieved by injection seeding. The design of this laser is being incorporated into NASA's SPARCLE (SPAce Readiness Coherent Lidar Experiment) wind lidar mission. Laser output energy ranging from 500 mJ to 2 J is required for an operational space coherent lidar. We previously developed a high energy Ho:Tm:YLF master oscillator and side pumped power amplifier system and demonstrated a 600-mJ single frequency pulse at a repetition rate of 10 Hz. Although the output energy is high, the optical-to-optical efficiency is only about 2%. Designing a high energy, highly efficient, conductively cooled 2-micrometer laser remains a challenge. In this paper, the preliminary result of an end-pumped amplifier that has a potential to provide a factor 3 of improvement in the system efficiency is reported.

Yu, Jirong↗