C.T. Harris

Arrays of gated field‐emitter cones having 0.32 μm tip‐to‐tip spacing

We have reduced the gate voltage required to achieve a given emission current density in field‐emitter arrays by scaling down the gate‐to‐tip and tip‐to‐tip spacing to the unprecedented levels of 0.08 and 0.32 μm, respectively. The submicrometer features of our arrays are patterned using interferometric lithography. Electrical tests of arrays we have fabricated have shown a record low turn‐on voltage of 8 V for cesiated molybdenum emitters. Emission current densities of 1600 A/cm2 have been obtained, which is also a record for such structures. These arrays provide large advantages for applications such as flat panel displays and microwave devices.

Near-diffraction-limited diode laser arrays by wavelength beam combining

We demonstrate 35 W output peak power with M2 approximately 1.35 in both dimensions from a 100 element, 100 microm pitch slab-coupled optical waveguide laser diode array using wavelength beam combining.

AlGaAs-InGaAs slab-coupled optical waveguide lasers

The slab-coupled optical waveguide laser (SCOWL) concept, recently proposed and demonstrated, is extended to the AlGaAs-InGaAs-GaAs material system. Both 980- and 915-nm SCOWL devices feature a nearly circular large-diameter single-spatial mode that can be butt coupled with high efficiency to a single-mode fiber. Single-ended continuous-wave output powers of greater than 1 W have been obtained at 980 nm.

Slab-coupled 1.3-μm semiconductor laser with single-spatial large-diameter mode

A high brightness semiconductor diode laser structure, which utilizes a slab-coupled optical waveguide region to achieve several potentially important advances in performance, is proposed and experimentally demonstrated using a simple rib waveguide in an InGaAsP-InP quantum-well structure operating at 1.3-/spl mu/m wavelength. These lasers operate in a large low-aspect-ratio lowest-order spatial mode, which can be butt coupled to a single-mode fiber with high coupling efficiency.

High-Brightness Wavelength Beam Combined Semiconductor Laser Diode Arrays

We report the wavelength beam combining of an array of high-power high-brightness 970-nm slab-coupled optical waveguide lasers. A 50-W peak power under quasi-continuous-wave (CW) operation was measured in an output beam with a beam quality of M_x,y ²=1.2, and 30 W under CW operation was measured with a beam quality of M_x,y ²=2

Bright‐field analysis of field‐emission cones using high‐resolution transmission electron microscopy and the effect of structural properties on current stability

High‐resolution transmission electron microscopy has been used to analyze 150 nm diameter by 150 nm high polycrystalline molybdenum field‐emission cones. The analysis shows that the cones comprise 5 to 10 nm thick grains with tips having gross radii of curvature of about 5 nm and protrusions having radii of curvature of about 1 nm. Such small protrusions may explain why analysis of experimental emission data indicates that the effective emission area of such tips is only 0.1 to 0.5 nm.2 Furthermore, the fact that the structure is composed of small grains indicates that there is a substantial number of molybdenum atoms at grain boundaries and that many configurations of grains and boundaries are possible with minimal free energy. A qualitative model is proposed which links the structural properties to current stabilization and hydrogen passivation effects.

High-brightness slab-coupled optical waveguide laser arrays

We have constructed high brightness slab-coupled optical waveguide laser arrays. Devices in the array emit in large nearly circular single-spatial modes. We have shown that optical cross-coupling in closely spaced devices is not an issue for maintaining single-mode output, including the effects of slab-coupling. By appropriate heat-sinking, we have shown linear continuous-wave power densities of 98 W/cm along the array emission aperture.

High-power nearly diffraction-limited AlGaAs-InGaAs semiconductor slab-coupled optical waveguide laser

Beam-quality measurements on the output of a 915-nm AlGaAs-InGaAs-GaAs slab-coupled optical waveguide laser (SCOWL) are reported. This device had a nearly circular mode (3.8 /spl mu/m by 3.4 /spl mu/m 1/e/sup 2/ widths in the near-field) and was capable of a single-ended continuous-wave output power of greater than 1 W. Measurements of M/sup 2/ indicate that the SCOWL output beam is nearly diffraction-limited in both directions with M/sub x//sup 2/ /spl sim/ M/sub y//sup 2/ /spl sim/ 1.1 over the entire range of output powers measured.

Ohmic contacts to n-type GaSb and n-type GaInAsSb

An investigation with the objective of improving n-type ohmic contacts to GaSb-based devices is described. This study involves a series of n-GaInAsSb and n-GaSb samples with varying doping, grown on semi-insulating (SI) GaAs substrates. These samples were fabricated into mesa-etched, transfer-length method (TLM) structures, and the specific-contact resistivity and sheet resistance of these layers as a function of majority electron concentration were measured. Extremely low specific-contact resistivities of about 2 × 10−6 Ω-cm2 and sheet resistances of about 4 Ω/▭ are found for n-type GaInAsSb doped at about 3 × 1018 cm−3.

High-brightness slab-coupled optical waveguide lasers

We have been developing a high power, high brightness semiconductor diode laser concept, the Slab-Coupled Optical Waveguide Laser (SCOWL). This laser concept is based upon slab coupling, in which a large, multimode waveguide is converted to a large, single mode waveguide by means of slab coupling of the higher order waveguide modes. SCOWL devices feature large, nearly circular mode sizes (≈4 x 4 &mgr;m and larger) and low modal loss, leading to low gain per unit length, allowing for the construction of long (≈1 cm cavity length) devices. These characteristics allow for high single mode output power. For 980-nm AlGaAs/InGaAs/GaAs-based SCOWL devices, we have demonstrated > 1 W CW output power in a single spatial mode, with brightness levels of > 100 MW/cm2-str. We have constructed high power arrays of SCOWL devices with bar widths of 1 cm and cavity lengths of 3 mm, and have demonstrated > 90 W under CW operation. By using the technique of wavelength beam combining (WBC), which is analogous to wavelength division multiplexing in optical communications, we have been able to combine the outputs from the elements of a SCOWL array to obtain 50 W peak power (30 W CW) with nearly diffraction-limited beam quality. These SCOWL arrays combined by WBC have demonstrated record single bar brightness levels, 3.6 GW/cm2- str. The WBC SCOWL approach is inherently scalable, and offers a route to obtaining kW-class, nearly diffraction limited output from an all-diode laser source. We have also recently extended single SCOWL devices to the multi-Watt regime, demonstrating 2.8 W CW output power from a 980-nm SCOWL with a novel design.