The University of Central Florida is taking responsibility for the operation of a unique long-path secure laser range facility on Air Force property on Merritt Island, just south of the Kennedy Space Flight Center. This facility, the Innovative Science & Technology Experimentation Facility, (ISTEF), provides unsurpassed options for laser-based experiments in rocket and satellite hyper-spectral imaging, precision laser illumination and ranging, atmospheric propagation across water, swamp and dry land, and other applications. This project plans to locate at this facility several laser-based experimental programs that are long-range extension studies of programs currently ongoing on the UCF campus. They are programs pursuing (i) the propagation of self-channeled femtosecond laser light through the atmosphere for unique propagation and interaction effects, (ii) the development of stand-off optical technologies for trace element explosives detection(iii) high-power eye-safe, (2ìm) laser propagation, ranging and imaging of rockets and satellite instrumentation. The intellectual merit of the proposal is rooted in the new avenues of fundamental science of long range laser propagation and effects that will be enabled by this proposal. This science will have direct benefit to technologies needed by the nation?s intelligence community for national security needs. Providing access to the NCMR university partners, to UCF and other universities will open access to this facility for field station student training in advanced concepts of laser propagation, interaction and effects, spectroscopy, sensing and imaging.

Project Report

Recent years have seen a phenomenal rise In the capabilities of high power fiber lasers. Power exceeding 10 kW is now achievable in single-mode fiber and the race is on to break the 100 kW mark. This has been enabled by the development of high-power 976 nm diodes which are ideally matched for efficiently pumping the 1030-1080 nm transition in ytterbium (Yb)-doped silica fiibers. In the shadow of this remarkable development we are now witnessing a similar growth pattern for thulium (Yb)-doped fiber lasers with wavelength of 1850-2100 nm. These lasers possess rather unique characteristics. Pumped by 790 nm diodes, the excitation scheme uses a cross-relaxation process that results in two-for-one photon generation with slope efficiencies approaching 70%. Powers approaching the kW level are now achievable. While the development of compact, high power, high efficiency, and high brightness Yb fiber and thin disk lasers has led to many advances in materials processing applications such as laser cutting and remote welding, the ~1 µm output wavelength of Yb:fiber lasers is generally not appropriate for laser applications requiring long distance propagation through free-space due to the possibility of accidental blindness from scattered or reflected laser radiation. On the other hand, Tm fiber lasers are well within the "eye-safe" regime, where the risk of permanent blindness is significantly reduced, as this radiation is strongly absorbed by the cornea and therefore cannot reach the lens or retina to cause damage. We have performed new experiments where we exploit the broad >200 nm spectral bandwidth of Tm fiber lasers for both tunability and generation of ultrashort pulses. We have explored the capabilities of conventional gratings, fiber Bragg gratings, volume Bragg gratings, and guided mode resonant fibers to produce spectrally tunable high power (200 W) laser sources with narrow (~50 picometer) linewidth, and have examined the benefits of these approaches to reaching 100 kW power levels. We further have secured a Cooperative Research and Development Agreement for access to the Innovative Science and Technology Facility (ISTEF) laser range on Cape Canaveral Air Force Station, Florida, where we have performed the first long range (1 km) atmospheric transmission tests with a high power Tm fiber laser. The intellectual merit of the study is in the characterization of Tm fiber as a medium for tunable high power laser output and ultrashort pulse generation and its application to long-range atmospheric propagation. Studies of the tunability of the high-power laser source using conventional gratings, fiber and volume Bragg gratings, and guided mode resonant fibers will enable the development of 100 kW laser sources for characterization of turbulent atmospheres and sensing of chemical signatures at long distances. The 1 km propagation studies demonstrate the applicability of the source to applications requiring beam delivery and sensitivity at long distances. The broader impacts of the study are in the development of an eye-safe source for remote applications, which will significantly reduce the risk for accidental blindness. Additionally, we have secured access to ISTEF for Intelligence Community Research through a Cooperative Research and Development Agreement. The unique capabilities of ISTEF enable new capabilities for long range propagation, stand-off sensing, and atmospheric monitoring to supplement existing research programs within CREOL and the Townes Laser Institute. ISTEF will now serve as a facility for academic research supporting defense related applications.

National Science Foundation (NSF)
Division of Information and Intelligent Systems (IIS)
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Sylvia J. Spengler
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University of Central Florida
United States
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