George P. Arnold

Parametric oscillator: HF oscillator–amplifier pumped CdSe parametric oscillator tunable from 14.1 μm to 16.4 μm

A singly resonant CdSe parametric oscillator with tunable output from 14.1 microm to 16.4 microm is described. The oscillator, pumped by the 2.87-microm line from an HF oscillator-amplifier, is resonant on the signal near 3.5 microm and has produced idler outputs of 100 microJ at 16 microm. Bandwidths varied over the tuning range from 9 cm(-1) to 1.8 cm(-1). Techniques for obtaining a highly coherent HF laser pump beam are presented. The uniform beam from the gain-saturated amplifier allows the use of Fresnel diffraction theory to produce a nearly uniform pump beam at the oscillator cavity.

Neutron Diffraction Study of Ice Polymorphs under Helium Pressure

Neutron diffraction studies of several of the D2O ice polymorphs were made with helium pressures to 3.5 kbar. Volume compressions (ΔV / V) were obtained for ices Ih, Ic, and IX at 2.1 to 2.8 kbar. The equilibrium phase boundaries between ices I–II and I–III in the presence of helium are shifted toward higher pressure values. The crystal structures of ices Ih, Ic, II, and IX at approximately 2.5 kbar are the same as the structures found for these ice forms at atmospheric pressure. A tetragonal structure is indicated for ice III with lattice parameters at − 23°C and 2.7 kbar of a = 6.674 ± 0.015 A and c = 6.97 ± 0.03 A. The c / a ratio for ice IX has been found to be 1.000 ± 0.003 both at 1 bar and at 2.8 kbar.

Magnetic Properties of PrAl2 and ErAl2

The magnetic properties of PrAl2 and ErAl2 have been investigated by neutron‐diffraction and susceptibility measurements on powder samples of the above compounds. The susceptibility data show that both compounds obey the Curie‐Weiss law; the effective moment per molecule in the paramagnetic region is 3.5±0.05 μB for PrAl2 and 9.2±0.1 μB for ErAl2. The neutron‐diffraction measurements confirm that these compounds are ferromagnetically ordered below a Curie temperature of 34°K for PrAl2 and 14°K for ErAl2; the respective saturated ordered moments at the rare earth atom sites are 2.94±0.05 μB and 8.3±0.3 μB. The magnetic form factor data from the ErAl2 coherent magnetic reflections are in good agreement with similar data obtained by other investigators on an Er single crystal. The magnetic scattering intensity of the (111) reflection from PrAl2 was measured just below the Curie temperature TC in order to determine the long‐range magnetic‐order temperature dependence. The results show that the spontaneous mag...

Magnetic Structure of DyAg

Neutron‐diffraction measurements on the intermetallic compound DyAg show that this material is antiferromagnetic below a Neel temperature, TN, of 51°±1°K; this magnetic structure is in agreement with previous susceptibility data. The measured ordered moment on the Dy atom sites is 9.8±0.5 μB which is essentially the full moment to be expected from the free Dy3+ ion. The observed antiferromagnetic structure is in disagreement with predictions derived from the Ruderman—Kittel—Yosida indirect exchange interaction. Molecular field calculations based on TN show that the exchange energy, |Jex|/k, is in the range from 1.5° to 2.2°K.

Magnetic Properties of TbIn3, TbPt3 and HoIn3

Neutron‐diffraction measurements made on powder samples of TbIn3, TbPt3, and HoIn3 show that all of these compounds exhibit antiferromagnetism below Neel temperatures of 37 ± 1°K, 20.5 ± 0.5°K, and 11.5 ± 0.5°K, respectively. The magnetic reflections from TbPt3 can be indexed on a doubled chemical cell of cubic symmetry. A possible magnetic model consists of an arrangement where the Tb moments are aligned in opposite directions in adjacent (111) magnetic planes. The magnetic reflections from TbIn3 and HoIn3 can be indexed on a doubled chemical cell of tetragonal symmetry. An appropriate magnetic arrangement is one in which the rare‐earth moments are aligned in opposite directions in adjacent (110) magnetic planes. For TbIn3 the moment direction makes an angle of 10 ± 5° with the unique or c axis of the magnetic cell; for HoIn3 the corresponding moment direction is 58 ± 5°. The saturation ordered moment on the rare‐earth atom sites in all three compounds is approximately 10% less than the calculated or exp...

Rapid recording of infrared spectra from pulsed chemical lasers

A method is described for rapidly recording permanent ir spectrograms of the output of a pulsed chemical laser. The method also lends itself to the simultaneous observation of the time behavior of several spectral lines. Spectra from an HF laser under different operating conditions are reported to demonstrate the utility of the method.

Magnetic Properties of DyPt3 and DyIn3

Neutron‐diffraction measurements made on powder samples of the intermetallic compounds, DyPt3 and DyIn3, show that these compounds exhibit antiferromagnetic ordering below Neel temperatures of 13.2° ± 0.3°K and 24° ± 0.5°K, respectively. The magnetic reflections from DyPt3 can be indexed on a doubled chemical cell of cubic symmetry. A suitable magnetic model consists of an arrangement where the Dy moments are aligned in opposite directions in adjacent (111) magnetic planes. For DyIn3, the magnetic reflections can be indexed on the doubled chemical cell of tetragonal symmetry. An appropriate magnetic model is one in which the Dy moments are aligned oppositely in adjacent (110) magnetic planes. The moment direction makes an angle of 27° ± 5° with the unique axis of the tetragonal magnetic cell. The saturated ordered moment is 9.0 ± 0.3 μB per Dy atom for DyPt3 and 8.8 ± 0.3 μB per Dy atom for DyIn3. The magnetic ordering process as a function of temperature closely follows a Brillouin function for DyPt3; th...

Nonlinear Loss in Ge in the 2.5–4-μm Range

Because of its high reflectivity and low absorption Ge has often been used as an output coupler or beam splitter in pulsed CO2 lasers operating at 10.6 μm. We report here some measurements which indicate that Ge may not be suitable for these uses in the 2.5-4 μm range, since severe attenuation can exist for moderate-power pulses. Measurements were made on a 5.1-mm thick plane-parallel disk of optical quality Ge. When the Ge was placed in the output beam of a pulsed HF laser fitted with an unstable resonator, transmission values were lower than the constant value of 0.46 ± 0.01 obtained in the 2-11.5 μm range with a spectrophotometer. The anomalous transmission effect was investigated over a wider range of intensity by placing the Ge in the converging beam from a 79-cm focusing mirror. After passing through the Ge the beam entered a calorimeter. A sapphire splitter before the Ge directed a fraction of the incident beam into a second calorimeter. The two calorimeter readings, together with the ratio obtained without the Ge, gave the Ge transmission as a function of incident laser energy. Figure 1 shows the reciprocal transmission as a function of incident peak intensity for the HF spectrum (2.6-3.1 μm) with the laser operating on SF6:C3H8. The data fits approximately a linear relation to be expected for a material in which the absorption coefficient is proportional to the intensity, as will be shown below. At the Ge position, 40 cm from focus, the beam cross section had an area of ~2 cm; the beam power was calculated using the known pulse length of 100 nsec FWHM. A second set of transmission measurements was made with the Ge 28 cm from focus. It should be noted that the transmission observed

ANISOTROPIC THERMAL EXPANSION OF REFRACTORY CARBIDES BY HIGH-TEMPERATURE NEUTRON DIFFRACTION.

The anisotropic thermal expansion of U2PtC2 (tetragonal), and UMoC2 (orthorhombic) has been measured using a high‐temperature neutron diffractometer. Coefficients of thermal expansion (units of 10−6/°C) are U2PtC2, α11=9.3±0.1, α33=10.1±0.8; UMoC2, α11=8.6±0.2, α22=15.5±0.5, α33=10±3.

Parametric oscillator: a grating-coupled CdSe OPO

The device reported is a CdSe OPO using no dichroic elements which produces 2-mJ pulses at 16 ..mu..m with a 0.3-cm/sup -1/ bandwidth. The cavity was designed to be tunable in the 15.5 to 16.5-..mu..m range. The useful life is now approximately 10/sup 4/ pulses, limited by grating damage. The pump laser is the HF oscillator--amplifier previously described. The only significant change made in the HF pump was to increase the focal lengths of the beam expander lenses by a factor of 2, allowing the use of a larger spatial filter and achievement of pump energies up to 100 mJ.