Robert C. Morris

Tunable-laser performance in BeAl 2 O 4 :Cr 3+

Broadly tunable laser operation has been obtained at room temperature from the vibronic bands of single-crystal BeAl(2)O(4):Cr(3+) under Xe-flashlamp excitation. Continuous tuning is obtained from 701 to 794 nm, with maximum power at 750 nm. Long-pulse operation employing 6.3-mm x 76-mm rods easily provides 500 mJ in 200-microsec bursts, whereas 70-mJ, 120-nsec pulses are obtained under Q-switch operation.

Diode-pumped Cr:LiSrAlF 6 laser

A Cr:LiSrAlF(6) laser is diode pumped with both commercial 10-mW visible laser diodes and a higher-power 100-mW cw, 265-mW pulsed diode. Polarization combination of pump diodes to reach threshold is demonstrated with two low-power lasers. Pumping with the high-power diode produced powers of 19.9 mW cw and 78 mW pulsed. Details of the Cr:LiSrAlF(6) crystal growth and high-power diode architecture are presented, along with optical characterization data for the laser resonator. Passive losses in the crystal are less than 0.1% cm(-1).

Disclination‐dislocation model of metallic glass structures

A new model for the structures of metallic glasses is proposed which is based on a continuous three‐dimensional network of mixed‐character disclinations containing a subnetwork (discontinuous) of dislocation segments which terminate on disclination jogs. Given the known geometrical properties of disclinations and their function as sources, sinks, and termination sites for dislocations, the mechanism of formation of the proposed double network structure is discussed. The approximate strain energy density of the model is derived from the known linear elastic solutions for disclinations. Using the measured elastic constants of several typical metallic‐alloy glasses, the calculated strain energy densities agree to within about 20% with the respective measured heats of crystallization, demonstrating the energetic feasibility of the model. The structural features of the model and its conceptual relationships to the microcrystalline and DRPS models are discussed and it is concluded that the disclination‐dislocat...

Spectroscopic properties and laser performance of Nd3+ in lanthanum beryllate

The neodymium‐doped lanthanum beryllate (La2Be2O5 : Nd3+ or BEL : Nd) laser crystal is monoclinic, space group C2h6‐C2/c. The fundamental vibration directions of light and the corresponding refractive indices have been determined as a function of wavelength. At 1 μm the indices are nX=1.9641, nY=1.9974, and nZ=2.0348. The energy levels of Nd3+ for the five lowest manifolds are presented. The low concentration limit for the Nd3+ 4F3/2 fluorescent lifetime in this crystal is 150 μsec and the two observed laser transitions have stimulated emission cross sections of 2.1×10−19 cm2 for E∥X and 1.5×10−19 cm2 for E∥Y. The laser wavelengths are 1.070 and 1.079 μm, respectively. In laser testing a higher slope efficiency was obtained in La2Be2O5 : Nd than in Y3Al5O12 : Nd (YAG : Nd). A Q‐switched output of 450 mJ from a 6.4‐mm‐diam by 76‐mm‐long X‐axis rod of BEL : Nd has been achieved for the 1.079‐μm transition, while a YAG : Nd rod of the same size in the same system yielded 160 mJ. The higher Q‐switched output ...

Rapid densification of porous carbon–carbon composites by thermal‐gradient chemical vapor infiltration

Porous carbon–carbon preforms, 10.8 cm o.d.×4.4 cm i.d.×3.0 cm thick have been densified in a one‐cycle, 26 h process. The disks are heated by induction, creating an inside‐out thermal gradient, and are exposed to cyclopentane vapor in a water‐cooled vacuum chamber. Rough‐laminar carbon microstructure is obtained; a compressive strength of 268 MPa is measured at 1.79 g/ cm3 density. The densification rate is monitored in real time. The precursor utilization efficiency is 20%–30%. Our patented process can be applied to other materials, has significant scale‐up potential and is economically competitive.

Excited‐state absorption in the pump region of alexandrite

Excited‐state absorption in alexandrite has been measured from 420 to 680 nm by using pulsed flash lamp pumping and a dye laser probe. The excited‐state absorption cross section is generally of the same order of magnitude as the ground‐state absorption cross section (10−19 cm2) and therefore may represent a large loss of energy from the pump source in a laser system. The results were confirmed at two wavelengths with a cw experiment in which 568‐ or 590‐nm radiation was used for pumping and probing.

Laser emission from the transition-metal compound LiSrCrF6.

We have demonstrated laser action in the transition-metal compound LiSrCrF6. A Ti:sapphire laser was employed to pump into the long-wavelength absorption wing in order to mimic the AlGaAs laser-diode wavelengths. Slope efficiencies greater than 30% were measured with a crystal having passive losses of the order of 3–5%/cm.

Compressive epitactic layers on single‐crystal components for improved mechanical durability and strength

Compressive epitactic layers grown on single‐crystal substrates are shown to substantially improve mechanical durability. In this study, neodymium‐substituted gadolinium gallium garnet (GGG) layers are grown on undoped GGG substrates. The layers are found to dramatically improve the abrasion resistance of the substrates, but to have only a slight effect on strength. Abrasion treatments, which cause up to 20 times decrease in the strength of substrates without epitactic layers, do not cause a significant decrease in the strength of substrates with these compressive surface layers. This permits the high strength of specially prepared strong substrates to be retained after abrasion.

Epitaxial waveguides of aluminum garnet

Waveguides of high refractive index aluminum garnets have been epitaxially grown on 〈111〉‐oriented crystal wafers of yttrium aluminum garnet (Y3Al5O12, YAG) and clad with epitaxial YAG. Epitaxy was by the liquid phase solution growth technique from supercooled mixtures of lead oxide and boron oxide, as is common for the epitaxy of iron garnets. One composition which is particularly suited for waveguides is Tb1.78Lu1.22Al5O12, which has a refractive index at 632.8 nm of about 1.854, as compared with 1.828 for YAG, and has no absorption bands in the visible and near IR spectra. Since aluminum garnets have melting points above 1900 °C, such waveguides should find application in high temperature optical sensors.

Development of a large-scale Nd:YAG growth process

Development of an automated steady-state process for Czochralski growth of flat interface Nd:YAG laser crystals is described. Steady-state is achieved through addition to the melt to maintain constant melt depth and composition. Interface flattening is accomplished through a controlled spin-up of crystal rotation during which characteristic changes in melt flow and crystal weight are observed. Combined steady-state/flat-interface growth has been demonstrated for sections up to 30 mm diameter x 110 mm long. In batch mode, without melt addition, flat interface YAG and Nd:YAG up to 52 mm x 220 mm, and undoped YAG up to 85 mm x 75 mm have been grown. In batchmode, gradual reduction of rotation rate is required to maintain interface contour and cross-sectional shape of the crystal as the melt height decreases.