Source: https://www.osapublishing.org/oe/abstract.cfm?uri=oe-17-5-3564
Timestamp: 2019-04-23 10:49:05+00:00

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Three conditions for non-collinear third harmonic generation by a PTR glass volume Bragg grating are demonstrated using infrared ultrashort pulse illumination. Each condition corresponds to a different angle of grating orientation and a separate generation mechanism. We identify the mechanisms as corresponding to sum-frequency generation, Bragg diffraction of 3ω, and a non-resonant Bragg condition involving three ω photons interacting with a nonlinear grating vector. Theoretical modeling is performed using wave vector additions and the results are compared to experimental measurements.
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Fig. 1. Experimental arrangement for investigating third harmonic generation and diffraction by transmitting Bragg gratings in PTR glass.
Fig. 2. Two-beam THG by a PTR glass TBG irradiated with IR femtosecond pulses: (a) wave vector additions of transmitted and diffracted photons to produce third harmonic (b) photograph from experiment. K - grating vector, ωT - transmitted photon, ωD -diffracted photon. Phase-matching is not satisfied.
Fig. 3. Wave vector conditions for non-collinear THG by a PTR glass TBG: (a) front surface diffracted THG (b) nonlinear grating THG, K NL - nonlinear grating vector (c) photographs of 3ω(2) and 3ω(3) from experiment at 1588 nm.
Fig. 4. Dependence of third harmonic intensity from PTR glass TBG on incident angle for (1) 3ω(i) beam (2) 3ω(ii) beam.
Fig. 5. Dependence of third harmonic intensity on incident angle for the two-beam THG case: (a) 3ω(i) beam (b) 3ω(ii) beam. 1 - theory 2 - experiment.
Fig. 6. Spectrum of femtosecond pulse shows an asymmetric profile.

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