CAREER: Back-conversion suppressed optical parametric frequency conversion: Nonlinear evolution dynamics for overcoming longstanding device limitations

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Lasers that can emit brief pulses of light have transformed industry and science. They are used for precise automotive machining, to identify cancer cells and to perform eye surgery, and to carry voices and data across the ocean. They are used to understand how plants harvest solar energy, how DNA withstands irradiation from ultraviolet light, and to study how the composition and structure of materials changes over time. They are used to study light induced nuclear fusion as an alternative energy source and to study the behavior of particles that have been accelerated to near the speed of light. However, only a few colors of light pulses can be obtained directly from lasers with sufficient intensity and brevity for these applications, and these colors are often not appropriate for the task at hand. In order to change the color of laser light, scientists use so-called “nonlinear optical” methods. By these methods, laser light can be shifted up or down in frequency and light can be amplified at colors not available from lasers by combining laser beams in a specialized optical device, typically a crystal or optical fiber. These methods are limited by an inherent behavior known as “back-conversion”: before light conversion is completed across the entire laser beam, the process begins to reverse. This makes nonlinear optical light conversion methods inefficient and limits the range of frequencies that can be generated. As a result, selectivity in the color of light comes at the cost of having less light available for the application, which in turn limits both the fundamental science and industrial applications that can be performed. The Principal Investigator aims to solve these problems by investigating new nonlinear optical methods with suppressed back-conversion. Devices consisting of crystals or optical fibers will be explored in order to prove that these light conversion methods can be carried out with unprecedented efficiency and covering a very broad range of frequencies, thus enabling new scientific and industrial applications of laser light. The Principal Investigator plans to use these methods in planned scientific studies during his career to enable investigation of the human vision process, new platforms for quantum information processing, and new methods for controlling the electrical, optical, and magnetic properties of materials through irradiation with laser light. The Principal Investigator will also develop related educational resources aimed at middle school through college level students in order to increase awareness of laser science and technology and to improve understanding of the engineering research process.In order to avoid the fundamental limiting problem of back-conversion in the evolution dynamics of nonlinear optical frequency converters and amplifiers, and thus to demonstrate light conversion and amplification devices with ultrahigh conversion efficiency and ultrawide bandwidth, the Principal Investigator will investigate two novel and potentially widely applicable concepts for nonlinear optical frequency conversion involving unusual propagation dynamics. First, a newly proposed method for suppressing back-conversion in optical parametric amplification will be attempted through the simultaneous phase matching of two wave-mixing processes, optical parametric amplification and second harmonic generation, in order to achieve signal amplification efficiency at or even beyond the quantum defect level. Implementations to be investigated will include both birefringent- and novel quasi-phase-matching approaches. Second, octave-spanning near- to mid-infrared photon down-conversion with a near unitary transformation matrix will be attempted via adiabatic four-wave mixing in an anti-resonant hollow optical fiber. This will be carried out by applying a pressure gradient to a microstructured hollow-core fiber that carries four laser beams simultaneously. The two forms of nonlinear evolution dynamics will be investigated by numerical and experimental methods, and devices will be investigated to prove feasibility.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.