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Motivation THG Dispersion and Compensation Experimental Setup

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Motivation THG Dispersion and Compensation Experimental Setup Characterization of a UV prism compressor for UV-IR pump- probe experiments Joseph Harrington1,3, Kurtis Borne1, Farzaneh Ziaee1, Kanaka Raju Pandiri1, Ruaridh Forbes2, Balram Kaderiya1, Yubaraj Malakar1, Travis Severt1, Itzik Ben-itzhak1, Artem Rudenko1, Daniel Rolles1 1 J.R. Macdonald Laboratory, Department of Physics, Kansas State University, Manhattan, KS 66506, USA 2Department of Physics, University of Ottawa, Ottawa, ON K1N 6N5 , Canada 3Department of Physics, Fort Hays State University, Hays, Kansas 67601, USA Motivation THG Dispersion and Compensation Studying molecular dynamics with short pulses Reducing Dispersion from THG [1] • Dissociation of Cyclohexadiene (CHD) by ultrashort UV • Dispersive properties of non-linear BBO crystals used for THG (266 nm) laser pulses Group delay dispersion (GDD) → Higher order expansion of spectral phase. • Under single UV-photon absorption, CHD excited to a → Varying propagation speeds of light pulse components due to wavelength ퟑ ퟐ 3 훌 퐝 퐧 fdafdsdependent refractive index will change pulse duration repulsive Q 0 potential energy curve 퐆퐃퐃 = ∗ 퐋 ퟐ훑퐜ퟐ 퐝훌ퟐ 퐜 → Using thinner crystals length (L ) reduces GDD • Resulting channel Hexatriene (HT) has a conical c intersection reached in 100 fs or less after excitation [1], so Prism Compressor → Introduces angular dispersion to counter positive GDD from the propagation through short pulse durations necessary to study these dynamics. air, spectrometer entrance window, and BBO crystals [3,4]. • UV pulse generation and characteristic → Prism pair gives negative GDD that can be optimized by tuning separation distance 푙. ퟐ • Third-Harmonic-Generation (THG) of a Ti:Sapphire laser (800 nm, 10 kHz, and 25 fs pulses) 훌ퟑ 퐝퐧 풅ퟐ풏 퐆퐃퐃퐩퐫퐢퐬퐦 = −ퟒ퐥 ퟐ + ퟒ ퟐ퐃풆−ퟐ • Non-linear process that causes [2] ퟐ훑퐜ퟐ 풅흀 풅흀ퟐ positive Group Delay Dispersion (GDD) • Compensate with negative GDD • Difference Frequency Generation (DFG) for cross-correlation measurement of pulse width through tunable prism pair setup Phase matching conditions in non-linear crystals will transmit frequency that is difference between two pump beams. Can use this signal for cross-correlation to measure pulse-width of Third Harmonic Experimental Setup Delay Stage COLd Target Recoil Ion Momentum Spectrometer (COLTRIMS) Cold gas jet To DFG/ COLTRIMS From Ti:Sapphire R:20 / T:80 Telescoping Mirror Focusing Mirror Spectra of fundamental Ti: Sapphire λcent = 783 nm ~ 1.5 eV Δλ = 75 nm THG Mirror Microchannel Plate used for amplifying ion signal. Yield Yield (arb. units) Beam-Splitter/Recombing Position measured with stacked delay line anode Prism Homogenous electric field guides ionic fragments to detectors Wavelength (nm) Spectra of THG Third Harmonic Generation (THG) CaF Prims compressors λcent = 259 nm ~ 5.0 eV 2 Δλ = 5 nm in folded geometry Difference Frequency Half Wave Plate Calcite Generation (DFG) BBO Second Harmonic BBO 흎 Yield Yield (arb. units) Third Harmonic ퟐ흎 P-polarized ퟑ흎 Dual Wave Plate Wavelength (nm) S-polarized Characterization of UV Pulses and results from UV-Pump-IR Probe experiments on CHD Cross Correlation: Acc = IIR t IUV(t − τ) dt DFG with Calcium Fluoride Prisms X-FROG Trace FWHM = 58 ± 1 fs Raw Data Gauss Fit Wavelength (nm) Normalized Normalized Yield (arb. units) Delay (fs) Delay (fs) DFG with Fused Silica Prisms Cross-Correlation Trace in Ar+ Raw Data FWHM = 76 ± 3 fs Raw Data FWHM = 46 ± 2 fs Gauss Fit Tcc = 46 fs Concluding Remarks Gauss Fit • Pulse Characterization using cross correlation TIR = 25 fs • Prism pair compressor in folded geometry is an effective • Future goals 2 2 2 Tcc = TIR + TUV way to reduce pulse duration • Extract kinetic energy release near conical • Switching material from fused silica to calcium fluoride intersection and compare to theoretical values 퐓퐔퐕 = ퟑퟗ ± ퟐ퐟퐬 improves performance • Angular distribution defined with angle between • Experimental results p-polarized laser field and dissociation vector Normalized Normalized Yield (arb. units) Normalized Normalized Yield (arb. units) Delay (fs) Delay (fs) • Found good overlap with low power UV and mid-range power IR • X-FROG Trace shows a GDD of roughly zero JRML personnel was supported by the Chemical Sciences, Geosciences, and Biosciences Division, Office of Basic Energy Sciences, Office of [1] Bucksbaum and Petrovic Faraday Discuss., 163, 475–484 (2013) Science, U.S. Department of Energy, Grant No. DE-FG02-86ER1349. This [2]R. Trebino et. al., Review of Scientific Instruments 68(9), 32777 (1997) work was partially supported by the National Science Foundation [3] J. Diels and W. Rudolf, Ultrashort Laser Pulse Phenomena, Second EPSCoR Track II Award No. IIA-1430493. KRP thanks NSF-EPSCOR Track Edition (Massachusetts, Academic Press, 2006). II project for their support. Also special thanks to the REU Grant No. [4] R. Fork, O. Martinez, and J. Gordon, Optics Letters 9, 150 (1984) PHY-1461251 for helping fund the research..
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