TECHNOLOGY AREA(S): Air Platform, Battlespace, Electronics

ACQUISITION PROGRAM: None or N/A NAE Chief Technology Office

OBJECTIVE: Develop a low space, weight, and power (SWaP) system fitting into a single rack unit for generating multiple laser frequencies to drive Rubidium85 (Rb85) transitions relevant to atom manipulation.

DESCRIPTION: The Navy is pursuing quantum sensing, both the development of new sensor technologies and the advancement of existing technologies. One of the challenges in this pursuit is simplifying and condensing complicated laboratory setups into a configuration that is able to be placed on a Navy platform. One such subset of quantum technologies is sensors based on Atom Interferometry. These sensors require simultaneous access to multiple atomic transitions for any given atom, which can result in complex electronic and optical setups. In particular, Rb85-based sensors require five separate, stabilized laser frequencies locked near the Rb85 D2 line [Ref 1-3] in order to drive the necessary atomic transitions. The characteristics of each of these laser outputs are listed in the specifications.

The currently employed method of accessing all necessary frequencies uses multiple independent lasers - each with separate saturated absorption locks. This method is demanding in terms of space and laser control electronics, and adds the complication of requiring multiple, independent locking mechanisms to stabilize each laser frequency and intensity. While adequate for laboratory demonstrations, this option is unrealistic for mobile sensor development. Integration onto a moving platform will require significant reduction in the number of optical components requiring active stabilization and lock down in order to maintain un-interrupted operation. Options that minimize the number of internal laser sources required to achieve the necessary output frequencies would have benefits in terms of complexity, ruggedness, and commonality of noise sources.

The optical and electronic packaging [Ref 4] should each be consolidated into a single 19�W x 19�D x 3.5�H rack with the optical rack having 5 polarization maintaining, FC/APC fiber coupled outputs. Consider the ability to actively stabilize frequency to within 10 kHz of the respective atomic transitions and intensity fluctuations below 0.1% of the output intensity; however, the saturated absorption reference does not necessarily need to be integrated into the completed package. All lasers must maintain polarization stability to within 0.01 degrees, which must be set to the fiber-coupled outputs. System must withstand the shock, vibration, pressure, temperature, humidity, electrical power conditions, etc. encountered in a system built for airborne use [Ref 4].
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Locked laser bandwidth: threshold: <200 kHz, goal <100 kHz.
Laser band and power specifications are as follows:
TRANSITION 1 (F=3 to F�=4): LASER 1 � red detuned by 6-10 MHz, coherent output, threshold: 200mW CW, goal: 300mW CW; LASER 2 � On resonance, coherent output, threshold: 6 mW, goal: 10 mW CW; LASER 3 � On resonance, coherent output, threshold: 60mW CW, goal: 80mW CW.
TRANSITION 2 (F=2 to F�=3): LASER 4: red detuned by 10-15 MHz, coherent output, threshold: 40mW CW, goal: 80mW CW.
TRANSITION 3 (F=2 to F�=3): LASER 5: red detuned by 1.5 GHz, coherent output, threshold: 40mW CW, goal: 60Mw CW.

The final system should be capable of operating under the conditions specified in [Ref 4]. Additionally, weight threshold: <30 lbs, goal: <10 lbs and power threshold: <200W, goal: <50W.

PHASE I: Develop the system design, including modeling, to determine the expected power output and phase stability, and demonstrate feasibility of the proposed solution. The Phase I effort will include prototype plans to be developed under Phase II.

PHASE II: Acquire necessary optical components, including lasers, Acousto-Optic Modulators (AOMs), lenses, and any other optical and electrical components required to accomplish the design developed during Phase I. Develop, demonstrate, validate and deliver prototype based on Phase I work.

PHASE III DUAL USE APPLICATIONS: Demonstrate operation of Phase II prototype in a magneto optical trap. Ruggedize the prototype to meet MIL-STD-810G [Ref 4] operational conditions. Commercial and academic use of laser cooled Rubidium will benefit from a simpler process for generating the necessary optical frequencies leading to less expensive and more reliable systems that utilize cooled rubidium. This could benefit existing industrial uses for cooled rubidium in atomic clocks, gravitational sensors, and any other application that requires laser cooling of rubidium.

REFERENCES:

1. Phillips, W. "Laser Cooling and Trapping of Neutral Atoms." Reviews of Modern Physics, Vol. 70, No. 3, 1998; https://journals.aps.org/rmp/pdf/10.1103/RevModPhys.70.721

2. Kasevich, M. and Chu, S. �Atomic Interferometry Using Stimulated Raman Transitions.� Phys. Rev. Lett. 67, 2, pp. 181-184, 8 July 1991. https://link.aps.org/doi/10.1103/PhysRevLett.67.181

3. Steck, D. �Rubidium 85 D Line Data.� (revision 2.1.6, 20 September 2013) https://steck.us/alkalidata/rubidium85numbers.pdf

4. MIL-STD-810G, DEPARTMENT OF DEFENSE TEST METHOD STANDARD: ENVIRONMENTAL ENGINEERING CONSIDERATIONS AND LABORATORY TESTS (31 OCT 2008) (Section 514.6C-1, 514.-C7 pages C-19, C-20). http://everyspec.com/MIL-STD/MIL-STD-0800-0899/MIL-STD-810G_12306/

KEYWORDS: Laser; Atomic; Quantum; Rubidium; Multi-Band; Magneto Optic Trap; MOT