Ultrafast deep UV laser source by all intracavity fourth harmonic generation

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Title: Novel High-Power, Ultra-Violet LasersNon-Technical Description:The goal of this project is to develop an ultrafast, deep ultra-violet (UV) laser source by fourth harmonic generation. A modified t-cavity vertical external cavity surface emitting laser (VECSEL) is to operate in the 240-260nm range with pulse widths 10ps and peak powers 10W. The proposed design will eliminate the need for expensive and inefficient cavity stabilization electronics and will push the boundaries in various fields including: nonlinear optics, semiconductor lasers, cavity design, and ultrafast pulse generation. As part of the research, a new VECSEL gain material will be designed and grown to deliver the large gain bandwidth needed for short pulse generation while still providing high peak powers. This new gain material combined with a semiconductor absorber mirror in a t-cavity configuration will allow development of a new laser source that can enable future advancements in science, medicine, material processing, and engineering research. In addition, this research group will provide an excellent research experience for individuals from under-represented groups through REU programs and undergraduate research. Two undergraduate students are to be involved each year for summer and/or academic internship. Technical Description:The proposed research will implement a novel t-cavity configuration for fourth harmonic generation and eliminate the need for cavity stabilization electronics. Typically, fourth harmonic generation to the UV uses a source laser that is coupled into a series of external resonator cavities that recirculate the fundamental and second harmonic modes. These external cavities are very sensitive to minor movements which lead to phase variations of the beams and to large power fluctuations of the UV output. This situation requires that each cavity have their resonances locked to ensure stable outputs. Such systems are large, complicated, and expensive which limits their potential use outside of a laboratory environment. The proposed research will eliminate the need of the external cavity due to the all-internal nature of the design. Here, the fundamental field is frequency doubled in a nonlinear optical (NLO) crystal for second harmonic generation. As the frequency doubled field is orthogonally polarized to the fundamental, an intra-cavity polarizing beam splitter expels this field into an alternate cavity path. While this is not a resonant cavity, the difficulty of injecting the light into an external resonator is eliminated. The second harmonic is generated inside this cavity and creates a large field in which another NLO crystal can efficiently frequency double this field to the UV. While stabilization electronics would improve the field build-up in the cavity, the research is focused on obtaining a stable high peak power output without additional elements.