S.R. Bowman

Spectroscopic analysis and laser modeling of neodymium-doped potassium lead chloride

Abstract We present a discussion of the low-phonon energy host material potassium lead chloride, KPb 2 Cl 5 , doped with neodymium. Crystal growth, spectroscopic measurements, and an analysis of the magnetic and electric dipole transitions based on the Judd–Ofelt model are presented. Concentration quenching of the fluorescence is also examined. Based on the spectroscopic data and the known resonances in energy spacing of the first three excited states in neodymium, we suggest the possibility of a 3-for-1 cross-relaxation process. This process may efficiently populate the first excited state, 4 I 11/2 , which we show to be metastable with lifetime on the order of a few milliseconds. Population inversion of this level should be possible enabling a laser based on the 5.5-μm, 4 I 11/2 to 4 I 9/2 transition.

Demonstration of a radiatively cooled laser

Summary form only given. We have developed a new optical pumping technique that minimizes the thermal loading in a solid-state laser system. This technique incorporates optical cooling directly into a laser medium. Lasing conditions were studied in which the waste heat required by stimulated emission is offset by cooling from anti-Stokes spontaneous emission. We call this condition a radiation balanced laser. Under ideal conditions, the heat load within the lasing medium can be completely eliminated. Perturbation analysis of the RBL condition reveals that thermal loads in the range of 5 W/cm/sup 3/ should be obtainable in scalable solid-state laser designs such as for Yb:KGd(WO/sub 4/)/sub 2/ lasers.

Laser oscillation from Ho 3+ doped Lu 2 O 3 ceramics

We report, for the first time, the laser oscillation from 2% Ho3+:Lu2O3 hot pressed ceramic. We have synthesized optical quality Lu2O3 nano-powders doped with concentrations as high as 5% Ho3+. The powders were synthesized by a co-precipitation method beginning with nitrates of holmium and lutetium. The nano-powders were hot pressed into optical quality ceramic discs. The optical transmission of the ceramic discs is excellent, nearly approaching the theoretical limit. The optical, spectral and morphological properties as well as the preliminary lasing performance from highly transparent ceramics are presented.

Single crystal fibers for high power lasers

In this paper, we present our recent results in developing cladded-single crystal fibers for high power single frequency fiber lasers significantly exceeding the capabilities of existing silica fiber based lasers. This fiber laser would not only exploit the advantages of crystals, namely their high temperature stability, high thermal conductivity, superior environmental ruggedness, high propensity for rare earth ion doping and low nonlinearity, but will also provide the benefits from an optical fiber geometry to enable better thermal management thereby enabling the potential for high laser power output in short lengths. Single crystal fiber cores with diameters as small as 35m have been drawn using high purity rare earth doped ceramic or single crystal feed rods by Laser Heated Pedestal Growth (LHPG) process. The mechanical, optical and morphological properties of these fibers have been characterized. The fibers are very flexible and show good overall uniformity. We also measured the optical loss as well as the non-radiative loss of the doped crystal fibers and the results show that the fibers have excellent optical and morphological quality. The gain coefficient of the crystal fiber matches the low quantum defect laser model and it is a good indication of the high quality of the fibers.

ORMOCHALCs: organically modified chalcogenide polymers for infrared optics

A novel method combining elemental sulfur and selenium was developed, yielding crystalline sulfur-selenium compounds. The compounds were melted, and an organic comonomer added. Once the organic comonomer was consumed, the viscous compound was vitrified and allowed to cool yielding organic-inorganic hybrid polymers that are termed Organically Modified Chalcogenide (ORMOCHALC) polymers.

Diode-pumped dysprosium laser materials

We are investigating materials for direct blue solid-state lasers assuming UV excitation with GaN based laser diodes. Room temperature spectroscopy is reported relevant to a proposed quasi-three level laser from the 4F9/2 level in trivalent dysprosium. Modeling based on these measurements suggests this is a promising new laser transition.

Lock-in holography using optically addressed multiple-quantum-well spatial light modulators

Perpendicular-field multiple-quantum-well optically addressed spatial light modulators have a response that saturates at high writing intensity. This limits the diffraction efficiency of low-fringe-visibility holograms. This effect is suppressed by use of the ability of these structures to subtract images rapidly. The modulator is exposed to a hologram with a spatially uniform beam, which is incoherent with the hologram, superimposed on top of it. Pulsing the hologram synchronously with the device drive voltage but leaving the uniform beam constant in time can build up the diffraction to large values even when the fringe visibility is low.

Cladding Pumped Single Crystal Yb:YAG Fiber Amplifier

We report on fabrication and optical properties of double clad single crystal Yb:YAG core fiber. For the first time, net gain is demonstrated in a cladding pumped Yb:YAG single crystal fiber structure.

Doped sesquioxide ceramic for eye-safe solid state laser materials

In this paper, we present our recent results in the development of Ho3+ doped sesquioxides for eye-safe solid state lasers. We have synthesized optical quality Lu2O3 nanopowders doped with concentrations of 0.1, 1.0, 2.0, and 5% Ho3+. The powders were synthesized by a co-precipitation method beginning with nitrates of holmium and lutetium. The nanopowders were hot pressed into optical quality ceramic discs. The optical transmission of the ceramic discs is excellent, nearly approaching the theoretical limit. The optical, spectral and morphological properties as well as the lasing performance from highly transparent ceramics are presented.

Recent advancements in transparent ceramics and crystal fibers for high power lasers

In this paper, we present our recent progress in the development of rare-earth (Yb3+ or Ho3+) doped Lu2O3 and Y2O3 sesquioxides for high power solid state lasers. We have fabricated high quality transparent ceramics using nano-powders synthesized by a co-precipitation method. This was accomplished by developments in high purity powder synthesis and low temperature scalable sintering technology developed at NRL. The optical, spectral and morphological properties as well as the lasing performance from our highly transparent ceramics are presented. In the second part of the paper, we discuss our recent research effort in developing cladded-single crystal fibers for high power single frequency fiber lasers has the potential to significantly exceed the capabilities of existing silica fiber based lasers. Single crystal fiber cores with diameters as small as 35μm have been drawn using high purity rare earth doped ceramic or single crystal feed rods by the Laser Heated Pedestal Growth (LHPG) process. Our recent results on the development of suitable claddings on the crystal fiber core are discussed.