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Erbium-doped gallium nitride (Er:GaN) is a promising gain material for solid-state high-energy lasers operating in the 1.5 μm wavelength window due to the superior optical properties and extremely high thermal conductivity of a GaN host crystal that permit high-power and high-temperature applications. We report the realization of all-crystalline GaN/Er:GaN/GaN embedded waveguide fiber structures using the hydride vapor phase epitaxy growth and re-growth technique, along with chemical–mechanical polishing processes. The Er:GaN core layer possesses an Er doping concentration of [Formula: see text] atoms/cm3, confirmed by secondary ion mass spectrometry measurements. X-ray diffraction measurements confirm, respectively, c-, a-, and m-plane orientations for top/bottom, side, and front/back cross-sectional cladding layers of the fiber structure with good single-crystalline quality. The 1.5 μm Er3+ emission was detected from each surface of the fiber structures via 980 nm resonant excitation. The effect of 1.54 μm light guiding by the fiber structure has been demonstrated. This work laid the foundation toward achieving all-crystalline core-cladding fibers based on GaN wide bandgap semiconductor with potential applications in the harsh environments of high powers, power densities, and temperatures.

Erbium-doped GaN (Er:GaN) quasi-bulk crystals are emerging as a promising novel gain medium for high energy lasers emitting at the retina-safe wavelength window of 1.5 μm. We report the polarization-resolved photoluminescence (PL) emission spectroscopy studies, which revealed that the pumping efficiency with the excitation polarization parallel to the c-axis of GaN ( E ⇀ | | c ⇀ ) is significantly higher than that with the excitation polarization perpendicular to the c-axis of GaN ( E ⇀ ⊥ c ⇀ ). This phenomenon is a direct consequence of the inherent polar wurtzite GaN lattice, giving rise to a net local field, surrounding each Er ion, along the c-axis of GaN. The temperature dependent behaviors of the PL emission spectra were explained in terms of the Boltzmann population distributions among sublevels within the 4I15/2 ground state and the 4I13/2 first excited state of Er3+ in GaN, thereby providing an improved understanding regarding the origin of the dominant emission lines observed near 1.5 μm. The results suggested that the polarization field in GaN can be exploited to enhance the effective Er excitation cross section by manipulating the polarization of the excitation light source.

Erbium doped gallium nitride (Er:GaN) bulk crystals have emerged as a promising optical gain material for high energy lasers (HELs) operating at the 1.5 μm “retina-safe” spectral region. Among the many designs of HEL gain medium, the core-cladding planar waveguide (PWG) structure is highly desired due to its abilities to provide excellent optical confinement and heat dissipation. We report the realization of a GaN/Er:GaN/GaN core-cladding PWG structure synthesized by hydride vapor phase epitaxy and processed by mechanical and chemical-mechanical polishing. An Er doping concentration of [Er] = 3 × 1019 atoms/cm3 has been attained in the core layer, as confirmed by secondary ion mass spectrometry measurements. A strong 1.54 μm emission line was detected from the structure under 980 nm resonant excitation. It was shown that these PWGs can achieve a 96% optical confinement in the Er:GaN core layer having a thickness of 50 μm and [Er] = 3 × 1019 atoms/cm3. This work represents an important step toward the realization of practical Er:GaN gain medium for retina-safe HEL applications.Erbium doped gallium nitride (Er:GaN) bulk crystals have emerged as a promising optical gain material for high energy lasers (HELs) operating at the 1.5 μm “retina-safe” spectral region. Among the many designs of HEL gain medium, the core-cladding planar waveguide (PWG) structure is highly desired due to its abilities to provide excellent optical confinement and heat dissipation. We report the realization of a GaN/Er:GaN/GaN core-cladding PWG structure synthesized by hydride vapor phase epitaxy and processed by mechanical and chemical-mechanical polishing. An Er doping concentration of [Er] = 3 × 1019 atoms/cm3 has been attained in the core layer, as confirmed by secondary ion mass spectrometry measurements. A strong 1.54 μm emission line was detected from the structure under 980 nm resonant excitation. It was shown that these PWGs can achieve a 96% optical confinement in the Er:GaN core layer having a thickness of 50 μm and [Er] = 3 × 1019 atoms/cm3. This work represents an important step toward the real...

We have produced 70%–75% 3He polarization by spin-exchange optical pumping in cells ≈100 cm3 in volume. The polarization achieved is consistent with known spin-exchange and spin-relaxation rates, but only when the recently discovered temperature dependence of 3He relaxation is included. Absolute 3He polarization measurements were performed using two different methods in two different laboratories. The results were obtained with either a spectrally narrowed laser or one type of broadband laser. Based on tests of several larger cells at pressures near 1 bar, we find that the power required to reach the same polarization is typically three times lower for the spectrally narrowed laser. This last result indicates that spectrally narrowed lasers will be important for obtaining the highest polarization in large volume neutron spin filters. Polarization in excess of 55% as obtained in cells up to 640 cm3 in volume and 70% polarization is anticipated with available increases in spectrally narrowed laser power.

Motivated by applications to neutron spin filters and recent advances in spectrally narrowed laser diode arrays (LDAs), we are exploring spin exchange optical pumping of 3He at pressures near 1 bar. Among our more interesting results has been the production of glass cells with extremely long relaxation times. The best of these has a lifetime of T1=840 h [where the polarization decays versus time, t, as exp(−t/T1)], dominated by the dipole–dipole contribution of 950 h at a 3He partial pressure of 0.85 bar. Using a broadband LDA, we have obtained 55% 3He nuclear polarization in this cell. These results are particularly relevant to the application of 3He-based neutron spin filters to neutron scattering and weak interaction experiments. Applications to magnetometry and polarized gas magnetic resonance imaging are also possible.