AFRL and the Air Armament Center collaborated in sponsoring Small Business Innovation Research (SBIR) efforts with Aerius Photonics, LLC (Ventura, California), and Photodigm, Inc. (Richardson, Texas), to develop a higheroutput semiconductor laser meeting the three preestablished requirements. Each company approached the problem differently. During its SBIR Phase I effort, Aerius Photonics successfully applied a new semiconductor laser technology, developed originally for telecommunications applications, to pulsed LADAR and range finders.^1,2 The Vertical-Cavity Surface-Emitting Laser (VCSEL) is grown vertically, with laser end mirrors (defined by Bragg grating layers) on the top and bottom surfaces (see Figure 1). Fabricated from layered semiconductor materials, a VCSEL’s structure is analogous to a stack of pancakes (see Figure 2). As the technology’s name indicates, the VCSEL emits light from one of its surfaces and, since its output aperture is round, typically produces a good beam structure for coupling via fibers or lenses (see Figure 3). However, due to the small size of the VCSEL’s laser cavity, the highest power ever generated by the commercial forms of these devices is approximately 1-2 W. In many commercial and military applications, power requirements may reach hundreds of watts.

Like most semiconductor lasers, the Aerius Photonics VCSELs rely on semiconductor wafers fabricated using common volume manufacturing techniques. VCSELs offer other advantages as well. For example, they require no mechanical packaging assembly to produce the laser, and technicians can test them on the wafer prior to additional processing. In addition, VCSELs produce a circular output beam that designers can easily integrate into devices without using complex lenses. This same output characteristic enables the assembly of beams into dense 2-D arrays (see Figure 4 on next page). Finally, VCSELs are energy-efficient and demonstrate greater wavelength stability over varying temperatures than do other semiconductor lasers.

Aerius Photonics engineers successfully employed VCSEL technology to produce 60 W of peak pulse power from a single VCSEL, achieving six times more output than previously reported for any other diode laser. They were also able to produce 30 W peak power pulses at 67 kHz, with more than 0.5 μJ per pulse at 15 ns pulse widths. These lasers are capable of operating in dense 2-D arrays with hundreds of elements, generating hundreds of times more output power per chip. Dr. Jon Geske, the Aerius Photonics principal investigator, summarizes the technology’s potential: “Partnering with the Air Force in the SBIR program, Aerius Photonics has been able to develop an entirely new source-laser approach for reduced costs in LADAR and laser range-finder applications. This is a real advancement in the field and will make a major impact on how future semiconductorbased LADAR systems are built for military and civilian applications.”