Air Force

Improved orientation patterned gallium phosphide template for mid-range infrared lasers

Combines the advantages of two nonlinear materials

Photonics

Air Force researchers have created compact, high-brightness, tunable, and room temperature operating laser sources in the mid-infrared range for use in laser countermeasures systems that can distract heat-seeking missiles from targeted aircraft.

Such lasers operating in the mid-infrared (IR) and terahertz (THz) region are in great demand for a wide variety of applications in defense; security (scanners, remote sensing of chemical and biological agents); industry (gas sensing, leak detection, pollution monitoring, process control); science (THz spectroscopy); and medical imaging.

Air Force laser research has many non-defense applications like the medical imaging procedure pictured.

The search for a solution has considered a number of different approaches, starting with binary and ternary semiconductor materials.

Recent advancements have been around the use of orientation patterned (OP) gallium arsenide (GaAs), which has broad IR transparency, high nonlinear optical susceptibility, and ability to be grown on OP-templates. However, 2-photon absorption in the 1 µm to 7 µm wavelength range has limited this material from taking advantage of many convenient pump laser sources in the important telecommunications wavelength of 1.55 µm.

In contrast to GaAs, gallium phosphide (GaP) has negligible 2-photon absorbtion in the 1 μm to 1.7 μm wavelength range and a comparable nonlinear susceptibility. GaP has twice the thermal conductivity (at much lower thermal expansion coefficients) and also broad transparency, which, in contrast with GaAs, conveniently starts in the visible portion of the spectrum facilitating alignment in an optical setup.

Unfortunately, OPGaP templates having a sufficiently high quality suitable for homoepitaxial growth are presently unavailable, partly due to the low quality (high etch pit density and poor parallelism) of the commercially-available GaP wafers, and partly due to the not-yet-optimized template preparation techniques. Thus, the OPGaP material grown by hydride vapor phase epitaxy (HVPE) on the available OPGaP templates is generally of low quality.

Air Force researchers have addressed the foregoing with a layered material that comprises an OPGaAs template, and a layer of GaP on the OPGaAs template. The OPGaAs template comprises a patterned layer of GaAs having alternating features of inverted crystallographic polarity of GaAs. The layer of GaP on the patterned layer of GaAs likewise comprises alternating regions of inverted crystallographic polarity of GaP, wherein the alternating regions correspond to the patterned layer of GaAs.

This high-quality OP material is ideally suitable for homoepitaxial growth and optimized for template preparation. Combining the advantages of the two most promising nonlinear materials, GaAs and GaP will accelerate the development of high power, broadly tunable laser sources in the IR which, in addition, will be offered with higher device quality and at a reasonably lower unit cost.

This US patent 9,647,156 is related to US patent 9,777,404.

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