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Development of Line-narrowed Diode Pump Sources for DPAL systems


OBJECTIVE: Develop line-narrowed, frequency stabilized diode pump sources to allow efficient resonant optical pumping of alkali laser systems. DESCRIPTION: This topic addresses diode technologies focused on enabling advanced closed cycle flowing media laser systems that offer compact directed energy system solutions for future ballistic missile defense applications. A promising example is the Diode Pumped Alkali Laser (DPAL). DPALs offer the potential for high power and efficient operation by leveraging the advantages of solid state and gas laser systems. These lasers are produced by direct optical pumping of alkali atoms in the vapor phase. The extremely low quantum defect of the alkali system minimizes thermal loading and, like other gas lasers, the gain medium can be flowed to reduce thermal management requirements. One key to producing efficient systems is matching the absorption linewidth of the gain media to the emission bandwidth of the diodes. Absorption linewidths are typically on the order of 0.01 nm to 0.1 nm while the diode emission is typically on the order of a few nanometers. Previously, in order to obtain sufficient overlap, a combination of pressure-broadening of the gain medium and diode linewidth narrowing using external cavities was used. The pressure-broadening can lead to detrimental effects in laser performance, such as beam quality degradation. Additionally, the diode-narrowing techniques are expensive and difficult to implement, thus limiting their practical use. A particular area of interest includes enabling technologies and support systems for the high-power optical pumping of alkali vapor atoms. Semiconductor diode laser technology presents the most cost-effective and scalable method to obtain the high powers and narrow spectroscopic linewidths required for these applications. Research and development is needed to realize scalable narrow-linewidth wavelength-stabilized laser diode pump sources for DPAL applications. The availability of these high-power spectroscopic pump sources would also find use in industrial and medical applications such as spin-exchange optical pumping (SEOP). With an efficient optical pump source, diode-pumped alkali vapor lasers have the potential for scaling to extremely high-power levels for industrial and military applications. The main impediment to achieving these power levels has been the availability of high-power narrow spectral line-width laser diode pump sources. Traditional efforts to produce narrow-line high-power diode laser pump sources typically rely on one of three methods, each with inherent tradeoffs and limitations. Technologies that are presented should meet or exceed the following requirements: 1) Diode emission bandwidth less than or equal to 0.05nm. 2) Center frequency locked to the D2 transition of one of the alkalis of interest. Rubidium is of highest interest to MDA, Cesium is the second highest, and Potassium is the third. 3) The long-term frequency drift cannot exceed 3GHz. The offeror should also consider the time it takes for the system to turn on and stabilize, as ultimately this will be required to be on the order of a few seconds. Technical approaches focused on or including 2D surface emitting diode laser architectures are of specific interest. PHASE I: Demonstrate in Phase I through modeling, analysis, and proof-of-principle experiments of critical elements of the proposed technology that the proposed approach is viable for further investigation in Phase II. Phase I work should clearly validate the viability of the technology proposed to meet the operational environment for directed energy applications in a component critical performance demonstration. Phase I should also result in a clear technology development plan, schedule, transition risk assessment, and requirements document. PHASE II: The Phase II objective is to validate a scalable and producible technology approach that MDA users and prime contractors can transition in Phase III to their unique laser application. Validate the feasibility of the proposed concept developed in Phase I by development and demonstration of a key components brassboard and the execution of supporting laboratory/field experiments to demonstrate technology viability. Validation would include, but not be limited to, system simulations, operation in test-beds, or operation in a demonstration subsystem. The goal of the Phase II effort is to demonstrate technology viability and the offeror should have working relationships with system and payload contractors. PHASE III: In this phase, the contractor will apply the innovations demonstrated in the first two phases to one or more MDA element systems, subsystems, or components. The objective of Phase III is to demonstrate the scalability of the developed technology, transition the component technology to the MDA system integrator or payload contractor, mature it for operational insertion, and demonstrate the technology in an operational level environment. A partnership with a current or potential supplier of MDA element systems, subsystems or components is highly desirable as is interaction with OSD High Energy Laser Joint Technology Office programs. COMMERCIALIZATION: High power laser components have numerous commercial and other government agency applications in metal cutting, material processing, welding, remote sensing (both terrestrial and space), satellite communications, power beaming, and weather sensing. Outside of MDA, numerous other DoD applications of the technology include tracking, designation, directed energy, demilitarization of munitions, and IED destruction.
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