TECHNOLOGY AREA(S): Battlespace, Electronics, Sensors

ACQUISITION PROGRAM: NAVSEA 073, Undersea Technology

OBJECTIVE: Develop a 3-wavelength band (Ultra Violet (250 nm), Visible (500 nm), Near infrared (1 um) Pulsed Fiber Laser System for Marine Wave Boundary Layer Atmospheric characterization.

DESCRIPTION: The Navy seeks technology that is oriented toward a deeper experimental and theoretical understanding of maritime turbulence and laser light propagation in the marine boundary. Ocean evaporation is occurring within a very thin molecular layer at the surface. However, there are indications that turbulent structures in the ocean and atmospheric mixing layers play a critical role in determining the water vapor flux. Current measurement techniques, such as Doppler Velocimetry (LDV) technique, are limited to resolutions of 0.5 meters or greater and fall short of the required millimeter level resolution. A new type of spectral imaging modality and instrumentation is required that will increase our understanding of ocean evaporation and lead to better tools for measuring and modeling the near-marine boundary layer for optical and radio frequency Naval applications. This generalized understanding will significantly enhance beam optic directors, adaptive optics, and other turbulence mitigating techniques to enhance the reach and effectiveness of communication and defensive and offensive laser light engagement in the marine boundary layer.

The overall objectives of this STTR topic are to: 1) develop a system capable of measuring atmospheric turbulence near the ocean surface (0 to 60 feet), 2) develop models that can predict turbulent effects given a set of atmospheric and marine surface conditions, such as surface temperature, humidity, pressure, wind speed, wave, fog etc., that can effects marine wave boundary layer atmosphere and 3) develop a metrological instrument based on Raman light detection and ranging (LIDAR). A 3-band laser is an attractive solution offering high power across 3 octaves from the near-IR (NIR) to the Deep Ultraviolet (DUV). Such a multi-wavelength laser offers unique capabilities that allow measurement and modeling of key elements of the near surface marine layer by enabling the accurate fitting to Rayleigh and Mie scattering models from simultaneous analysis of 3 wavelengths. Adapting existing models or creating new physics-based models using data retrieved from the 3-band compact Raman laser system, at picosecond pulse in each band at minimum 1 mJ per pulse energy at 1 kHz repetition rate has the potential to enhance substantially Navy capabilities for deployed high power lasers operating the marine environment. The potential source will the based on the mature fiber laser technology and will make possible compact and power efficient laser systems capable of producing simultaneous UV, visible, and IR radiation at sufficient pulse energy, repetition rate, pulse width, and average power to characterize relevant maritime environments. The platform laser technology should be amenable to the development of a 3-band Raman laser system with Size, Weight, and Power (SWaP) for the integration into submarine sail and cost to facilitate widespread deployment as metrological tool for marine wave boundary atmospheric characterization. The 3-band laser also is the part of High Energy Laser (HEL) closed loop circuits to control the HEL beam on target. The proposed 3-band picosecond Raman laser shall be able to integrate into HEL system for target ranging and detection.

It is expected that the application will require a laser system with performance at or exceeding greater than 10W of average power in each band (UV, VIS, IR), pulse energies greater than 1 mJ, temporal pulse width of less than 1 ns for suitable ranging, pulse repetition rates between 1 kHz and at most 5 kHz, and a stable, narrow laser bandwidth of a few wavenumbers or less sufficient to distinguish Raman lines. Laser frequency drift (mitigated by stabilization schemes) may also be of concern at system level. At present to no such system is available to characterize the atmosphere simultaneously in all above three bands.

PHASE I: Develop a concept for a laser system based on model based engineering (MBE) as described in the Description. Demonstrate the feasibility of that concept through laser architecture modeling, simulation, and theoretical calculation. Ensure that the laser is capable of delivering producing greater than 10 W of average power in each band in stable picoseconds, with conversion efficiency in the high-power amplifier of approximately 45% including the combined loss and the unabsorbed pump. Show the laser emitted spectrum of the amplified pulses at different output powers at 3 separate band. Develop a Phase II plan. The Phase I Option, if exercised, will include the initial design specifications and capabilities description to build a 3-band picosecond Raman laser prototype solution based on MBE in Phase II.

PHASE II: Develop and deliver a prototype of a 3-band picosecond Raman laser system based on the concept developed in Phase I and the Phase II Statement of Work (SOW). Work with the Government to develop the test criteria for the prototype 3-band laser system. Deliver a 3-band laser system to the Navy for the evaluation of performance and further characterization for the purpose of Raman back scattering to characterize atmospheric, temperature, pressure, and humidity. Support the Navy for validation and additional testing to be qualified and certified for Navy use.

PHASE III DUAL USE APPLICATIONS: Support the Navy in transitioning the technology to Navy submarine platforms as a metrological tool for marine wave boundary data collection.

3-Band picosecond Raman laser technology shall have both commercial and DoD applications. This technology can improve a commercial ship�s localized weather condition prediction and update the weather software for safe operation�thereby improving LIDAR detection for range at day, night, and all-weather operations for both commercial and DoD applications.

REFERENCES:

1. Katz, Richard A. and Manzur, Tariq. "Laser beam propagation through an atmospheric transitional and turbulent boundary layer", Proc. SPIE 9456, Sensors, and Command, Control, Communications, and Intelligence (C3I) Technologies for Homeland Security, Defense, and Law Enforcement XIV, 945615 (May 23, 2015). https://doi.org/10.1117/12.2182680

2. Hufnagel, R. E. and Stanley, N. R. �Modulation Transfer Function Associated with Image Transmission through Turbulent Media�, J. Opt. Soc. Am., 54, 52-61 (1964). https://doi.org/10.1364/JOSA.54.000052

3. Wasiczko Thomas, Linda M., Moore, Chistopher I., Burris, Harris R., Suite, Michele, Smith Jr., Walter Reed, and Rabinovich, William. �NRL's Research at the Lasercomm Test Facility: Characterization of the Maritime Atmosphere and Initial Results in Analog AM Lasercomm�, Proc. SPIE, 6951, Atmospheric Propagation V, 69510S (April 18, 2008). https://doi.org/10.1117/12.783791

KEYWORDS: Raman LIDAR; Meteorological Instrumentation; Laser Beam Propagation; Maritime Environment; Turbulent Boundary Layer; 3-band Raman Laser System; picosecond Laser, 10-12 Second