Generation and Application of Ultrashort Coherent Mid-Infrared Electromagnetic Radiation PDF Download

Author: Scott Wandel
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Languages : en
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Book Description
Particle accelerators are useful instruments that help address critical issues for the future development of nuclear energy. Current state-of-the-art accelerators based on conventional radio-frequency (rf) cavities are too large and expensive for widespread commercial use, and alternative designs must be considered for supplying relativistic beams to small-scale applications, including medical imaging, security screening, and scientific research in a university-scale laboratory. Laser-driven acceleration using micro-fabricated dielectric photonic structures is an attractive approach because such photonic microstructures can support accelerating fields that are 10 to 100 times higher than that of rf cavity-based accelerators. Dielectric laser accelerators (DLAs) use commercial lasers as a driving source, which are smaller and less expensive than the klystrons used to drive current rf-based accelerators. Despite the apparent need for compact and economical laser sources for laser-driven acceleration, the availability of suitable high-peak-power lasers that cover a broad spectral range is currently limited.To address the needs of several innovative acceleration mechanisms like DLA, it is proposed to develop a coherent source of mid-infrared (IR) electromagnetic radiation that can be implemented as a driving source of laser accelerators. The use of ultrashort mid-IR high peak power laser systems in various laser-driven acceleration schemes has shown the potential to greatly reduce the optical pump intensities needed to realize high acceleration gradients. The optical intensity needed to achieve a given ponderomotive potential is 25 times less when using a 5-m mid-IR laser as compared to using a 1-m near-IR solid-state laser. In addition, dielectric structure breakdown caused by multiphoton ionization can be avoided by using longer-wavelength driving lasers. Current mid-IR laser sources do not produce sufficiently short pulse durations, broad spectral bandwidths, or high energies as required by certain accelerator applications. The use of a high- peak-power mid-IR laser system in DLA could enable tabletop accelerators on the MeV to GeV scale for security scanners, medical therapy devices, and compact x-ray light sources.Ultrashort mid-IR laser sources also play a vital role in the measurement and enhancement of material properties relevant for nuclear applications. For example, photoexcitation of graphene with femtosecond mid-IR laser pulses can be used to measure the time-resolved photoconductivity in graphene for its use in radiation detection. Graphene photodetectors have the unique ability to operate at room temperatures across a broad spectral region with ultrashort response times; however, achieving high efficiency in graphene detectors remains challenging due to graphenes weak optical absorption. The current methods and materials are not capable of operating at room temperature, do not respond at mid-IR wavelengths, or cannot achieve single-shot operation. Therefore, the metrology of ultrashort mid-IR laser pulses is needed to understand the mechanisms of photoconductive gain in mid-IR detectors to enhance detector efficiency. Advanced pulse diagnostic instrumentation is needed that performs reliably and efficiently over a broad spectral range for the metrology of ultrashort mid-IR laser pulses for applications of radiation detection, IR spectroscopy, and remote sensing for trace gas detection.This dissertation reports on the design and construction of a simple and robust, short-pulse parametric source operating at a center wavelength of 5 m. The design and construction of a high-energy, short-pulse 2-m parametric source is also presented, which serves as a surrogate pumping source for the 5-m source. An elegant method for mid-IR pulse characterization is demonstrated, which makes use of ubiquitous silicon photodetectors, traditionally reserved for the characterization of near-IR radiation. In addition, a dual-chirped parametric amplification technique is extended into the mid-IR spectral region, producing a bandwidth- tunable mid-IR source in a simple design without sacrificing conversion efficiency. The design and development of a compact single-shot mid-IR prism spectrometer is also reported, and its implementation in a number of condensed matter studies at the Linac Coherent Light Source (LCLS) at the Stanford Linear Accelerator Center is discussed. Rapid tuning and optimization of a high-energy parametric laser system using the mid-IR spectrometer is demonstrated, which significantly enhances the capabilities of performing optical measurements on superconducting materials using the LCLS instrument. All of the laser sources and optical technologies presented in this dissertation were developed using relatively simple designs to provide compact and cost-effective systems to address some of the challenges facing accelerator and IR spectroscopy technologies.