Diode-pumped Alkali Laser Key Energetics Parameters Measurement and Assessment

OUSD (R&E) MODERNIZATION PRIORITY: Directed Energy TECHNOLOGY AREA(S): Ground Sea; Weapons; Space Platforms; Air Platform The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws. OBJECTIVE: Design and conduct an experiment to measure and assess the electron energy distribution of the gain medium of a high-power diode-pumped alkali (rubidium) laser (DPAL) with high-pressure helium. DESCRIPTION: As DPAL systems scale up in power, they form a plasma that reduces the optical to optical efficiency, resulting in increased gas heating, poor size, weight, and power, and possible negative impacts to beam quality. An experimental understanding of the electron number density and the electron energy distribution function (EEDF) is needed for model validation to assess scaling potential. However, EEDF parameters involved in the lasing interactions have only been calculated, not directly measured. As the EEDF varies based on the environment, its measurement has proved difficult for parameter spaces of interest. This topic seeks methods for direct measurement of the EEDF that will enable the DPAL systems under development to scale to operationally relevant powers. The measurements are required to be made under a variety of buffer gas pressures, laser intensities, and rubidium densities. Techniques of interest for measuring these key parameters include but are not limited to Thomson Scattering, Stark Broadening, and microwave interferometry. PHASE I: Design an experiment to obtain measurements of EEDF (ion density). Phase I includes completing and delivering a methodology and design to measure the EEDF under relevant pump laser intensities, buffer gas pressures, and rubidium densities. Produce a cost estimate and schedule to carry out such an experiment. Identify long-lead items which must be procured. Work with the Government and independent evaluators designated by the Government to identify areas of improvement for the design to provide more relevant data. PHASE II: Complete the EEDF measurements experiment and deliver the data to the Government. Phase II includes updating the design of the Phase I experiment based on Government feedback. Procure equipment necessary for the experiment. Assemble experimental apparatus as required. Conduct experiments to collect data to measure the electron number density and the electron energy distribution function (EEDF). The measurement shall be made under a variety of buffer gas pressures, laser intensities and rubidium densities that will be decided together with the Government. Collect and analyze the data and deliver to the Government. Work with the Government and independent evaluators designated by the Government to identify areas of improvement for the experimental design and procedure to provide more relevant data. Implement changes based on feedback. PHASE III DUAL USE APPLICATIONS: The goal of this phase is to transfer the information and knowledge gained in Phase II to the DoD Diode Pumped Alkali Laser community, to include any industry partner that is involved in scaling the DPAL to weapon system power levels. This effort may include incorporating the information into a DPAL model. REFERENCES: O. Zatsarinny, et al., Electron collisions with Cesium atoms benchmark calculations and applications to an electron-pumped excimer, Plasma Sources, Science, and Technology, 23 #3, pp 1-7, (2014) Hai P. Le and Jean-Luc Cambier, Conservative algorithms for non-Maxwellian plasma kinetics, Phys. Plasmas, 24, 122105 (2017) M. S. Dimitrijevic and S. Sahal-Brechot, Stark Broadening of Neutral Potassium Lines, J. Quant. Spectrosc. Radiat. Transfer Vol. 38, No. 1, pp 37-45, (1985) V. M. Donnelly, Plasma electron temperatures and electron energy distributions measured by trace rare gases optical emission spectroscopy , J. Phys. D: Appl. Phys. 37 R217, (2004) D. W. Hahn and Nicolo Omenetto, Laser-Induced Breakdown Spectroscopy (LIBS), Part I: Review of Basic Diagnostics and Plasma Particle Interactions: Still-Challenging Issues Within the Analytical Plasma Community, Applied Spectroscopy, Vol. 64, Number 12, pp 335A-366A, (2010) KEYWORDS: DPAL; Diode-pumped Alkali Laser; Electron Energy Distribution Function; Ion Density