The Department of Defense, specifically the United States Air Force, is seeking proposals for the development of bulk KGd(WO4)2 crystals for solid-state Raman laser applications through a Direct to Phase II (D2P2) Small Business Innovation Research (SBIR) program. The primary objective is to establish a domestic supply of these crystals, which are critical for various military applications including Infrared Counter Measures and long-range sensing, with specific requirements for crystal sizes, damage thresholds, and coatings over a two-year development period. The initiative aims to address the current lack of domestic sources for these materials, which are essential for high-energy laser systems, with the project set to open for applications on May 28, 2025, and closing on June 25, 2025. Interested parties can find more information and submit proposals through the official SBIR website.

## Description

Solid state lasers are required for a vast array of Air Force platforms and systems, particularly for Infrared Counter Measures (IRCM), Directional Infrared Counter Measures (DIRCM), and long-range sensing applications. Emerging technology is driving laser source development towards multi-spectral and high energies needed to engage adversarial systems. There are currently no direct generation sources that meet these demands. The traditional approach of using parametric conversion nonlinear optics to provide spectral diversity can no longer necessarily support the evolving required high energies; parametric crystals are simply not available in sufficient sizes to cope with the anticipated pulse energy requirements needed today.Solid State Raman lasers could provide a solution to many of the issues. Materials such as Potassium Gadolinium Tungstate (KGW) have historically been grown to very large sizes. This class of laser material is highly adaptable to a number of configurations, ranging from a simple &ldquo;pass-through&rdquo; to operation as a resonator (external or intracavity), and as master oscillator power amplifiers (MOPA) devices. KGW can even be doped with primary rare earth elements such as Yb, Nd, Er, Tm, and Ho, to create a hybrid device that generates its own pump light to drive the Raman process. The Raman process itself is stimulated amplification of light that is inelastically scattered by the host material. Stimulated Raman conversion can be extremely efficient (&gt;70%) and can generate a range of wavelengths, each separated by a frequency that is characteristic of the Raman material being used. Stimulated Raman scattering is a third order optical nonlinearity and as such requires generally higher optical intensities than second order parametric processes. Fortunately, the bulk optical damage threshold for KGW is of the order of several hundred Joules per cm2, making it very suitable for scaling to high energies. However, there are currently no domestic sources available for this material.This Direct to Phase II (D2P2) SBIR is seeking to develop a commercial on-shore supply of bulk KGW crystals. Historically, bulk crystals of KGW have been grown by the Top Seeded Solution Growth (TSSG) technique with excess potassium tungstate added to the melt to account for volatility of this species and prevent nonstoichiometry. [1-5] KGW crystals have also been grown via Kyropoulos[6], and top nucleated floating crystal method [7], whereas the Bridgman technique has been demonstrated for the yttrium analogue of KGW.[8] The crystal sizes and quality obtained via TSSG and other techniques demonstrate a level of manufacturing maturity suitable for a D2P2 SBIR effort.Phase II SBIR Objectives:Year 1: 5 x 5 mm aperture with at least 25 mm path length; b-axis, (010) directionA/R coated to cover the first three Stokes wavelengths for green pumping and 1 micron pumping (can be separate coatings or a single coating to cover all the wavebands)Damage threshold for the finished crystals to exceed 20 Joules per square cm.Delivery of 1 finished crystals of each size and each waveband (i.e. 2 total per year)Year 2: 10 x 10 mm aperture with at least 50 mm path length; b-axis, (010) directionA/R coated to cover the first three Stokes wavelengths for green pumping and 1 micron pumping (can be separate coatings or a single coating to cover all the wavebands)Damage threshold for the finished crystals to exceed 20 Joules per square cm.Delivery of 2 finished crystals of each size and each waveband (i.e. 4 total per year)Phase III SBIR Objectives:Year 1: 25 mm x 25 mm aperture with at least 50 mm path length; b-axis, (010) directionA/R coated to cover the first three Stokes wavelengths for green pumping and 1 micron pumping (can be separate coatings or a single coating to cover all the wavebands)Damage threshold for the finished crystals to exceed 50 Joules per square cm.Delivery of five finished crystals of each size and each waveband (i.e. 10 total per year)Year 2: 50 mm x 50 mm aperture with at least 50 mm path length; b-axis, (010) directionA/R coated to cover the first three Stokes wavelengths for green pumping and 1 micron pumping (can be separate coatings or a single coating to cover all the wavebands)Damage threshold for the finished crystals to exceed 50 Joules per square cm.Delivery of five finished crystals of each size and each waveband (i.e. 10 total per year)

## Objective

The objective of this SBIR is to develop an on-shore commercial supply of bulk KGd(WO4)2 single crystals that can be used for various DoD applications. The bulk crystals toward the end of a Phase III should be 50 x 50 x 50mm to handle the anticipated lasing requirements.

## Phase I

In a Phase I effort, demonstration of a viable growth technique to produce monoclinic KGW crystals with sizes of 5 x 5 x 5mm would be required. The chosen crystal growth technique would be need to be scalable to the dimensions provided in the Phase III topic description. The Phase I effort wouldn't require demonstration of an AR coating or damage threshold measurements. Given the number of publications and knowledge based established this doesn&rsquo;t fit the &ldquo;establishing feasibility&rdquo; that accompanies Phase I efforts. Growth is feasible by TSSG especially and a few US-based small businesses have already proven capable of surpassing the Phase I requirements. Thus, a D2P2 is the more preferred method to bring this material to commercialization in an expedient manner. 

## Phase II

Year 1: 5 x 5 mm aperture with at least 25 mm path length; b-axis, (010) directionA/R coated to cover the first three Stokes wavelengths for green pumping and 1 micron pumping (can be separate coatings or a single coating to cover all the wavebands)Damage threshold for the finished crystals to exceed 20 Joules per square cm.Delivery of 1 finished crystals of each size and each waveband (i.e. 2 total per year)Year 2: 10 x 10 mm aperture with at least 50 mm path length; b-axis, (010) directionA/R coated to cover the first three Stokes wavelengths for green pumping and 1 micron pumping (can be separate coatings or a single coating to cover all the wavebands)Damage threshold for the finished crystals to exceed 20 Joules per square cm.Delivery of 2 finished crystals of each size and each waveband (i.e. 4 total per year)

## Phase III: Dual Use Applications

Year 1: 25 mm x 25 mm aperture with at least 50 mm path length; b-axis, (010) directionA/R coated to cover the first three Stokes wavelengths for green pumping and 1 micron pumping (can be separate coatings or a single coating to cover all the wavebands)Damage threshold for the finished crystals to exceed 50 Joules per square cm.Delivery of five finished crystals of each size and each waveband (i.e. 10 total per year)Year 2: 50 mm x 50 mm aperture with at least 50 mm path length; b-axis, (010) directionA/R coated to cover the first three Stokes wavelengths for green pumping and 1 micron pumping (can be separate coatings or a single coating to cover all the wavebands)Damage threshold for the finished crystals to exceed 50 Joules per square cm.Delivery of five finished crystals of each size and each waveband (i.e. 10 total per year)

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