SBIR-STTR Award

Ultra Short Pulse (USP) laser technology offers compelling capabilities for the defense, medical and material processing industries. The development of this technology into commercial devices has been limited mostly by the size, cost and pulse energies provided by current USP laser systems. Fiber-based USP lasers have dramatically decreased the size of this technology, but the amplification of high energy pulses is still necessary to achieve the desired success for commercial USP laser devices. Power scaling of fiber lasers and amplifiers requires increasing the signal mode size to avoid nonlinear impairments and optical damage. Established approaches to scalability are inherently limited since the signal mode becomes progressively more unstable with effects such as mode competition and scrambling as the size increases. As described in this proposal, the capability to scale fiber amplifiers beyond the 100 J/pulse range, in a single polarization state, with high beam quality and in a compact form factor is achieved using higher order mode (HOM) propagation. Higher order modes have demonstrated scalable mode size with a high degree of stability in passive fibers. They are also fully compatible with existing or enhanced all-glass pump combiners and fiber fusion and assembly techniques.

Benefit:
Commercially available fiber USP laser systems are robust and stable, but lack the output power and pulse energy necessary for applications that require higher ablation rates or beam propagation over long distances. Successful completion of the goals of this program will enable the exploration of DoD, medical and industrial USP laser applications where high pulse energy and high average power are required at eye safe 0x9D wavelengths. For example, distance interrogation, distance imaging and sensing, medical imaging, non-thermal materials processing, harmonic generation and two photon LIBS spectroscopy.

Keywords:
ultrashort pulse (USP), ultrashort pulse (USP), higher order modes (HOM), Amplifier, fiber-based, LASER

Ultrashort Pulse (USP) lasers fall into two broad classes: bulk optical systems and fiber-based systems. The former generate meaningful pulse energies but have limited real-world utility due to their size and reliability issues. Alternatively, fiber lasers are extremely robust and easy to use but traditionally have not had the average output power and pulse energy necessary for some applications. Because small form factor and reliability are of paramount importance for widespread adoption of USP technology, Raydiance, in collaboration with OFS Labs, is pursuing technology to dramatically increase amplification of USP signals within a fiber-based system. In Phase I work, Raydiance and OFS demonstrated the feasibility of using rare earth doped higher order mode (HOM) fibers as a gain fiber for amplifying eye safe 0x9D wavelength (1552 nm), chirped pulses. In Phase II, Raydiance and OFS propose to develop the components and gain fibers required to assemble an HOM fiber amplifier module. The module will then be integrated into a chirped pulse amplification (CPA) USP laser system for end to end system characterization. The Phase II Option plan includes the design, assembly and test of a packaged HOM fiber amplifier module for delivery to the Navy and integration into a laser system.

Benefit:
Successful completion of the goals of this Phase II SBIR will enable DoD and commercial USP laser applications in which high pulse energy and high average power are required at eye safe 0x9D wavelengths. Specific potential benefits for the Department of Defense, include applications for LADAR, terahertz generation, spectroscopy for chemical/biological/explosives detection, and IRCM/ECM applications. The most significant and immediate commercial applications include the micromachining of high value materials, in particular, next generation vascular stents and thin film photovoltaics used in solar panels. Both machining opportunities demand the capabilities provided by USP technology: extreme precision without collateral thermal or mechanical damage. Higher pulse energy provided by the proposed amplification technology would significantly impact ablation rates and, therefore, throughput rates in manufacturing environments. Higher throughput rates, in general, will speed the adoption of USP technology across a wide swath of micromachining sectors, including aircraft and engine manufacturing, microelectronics, and bio-MEMS applications.

Keywords:
LASER, Electro-optics, usp laser, amplification, fiber laser