Abstract

Ultrashort UV pulses are of great interest due to their wide ranging applications such as biosensing [5], high harmonic generation [3], and time resolved spectroscopy [4]. Hollow Core Fibers (HCF) play a critical role for ultrashort UV pulse generation through soliton dynamics [6], four wave mixing [2], or cross-phase modulation (XPM) [1]. We are developing a novel approach, first introduced at CLEO US 2022 [1], of generating few-cycle pulses in the 266 nm region using XPM which promises to deliver higher pulse energies than other approaches. Here XPM is used to broaden and compress third-harmonic pulses, with ~ 10 µJ pulse energy, of an 800 nm Ti:Sapphire amplifier, see fig. 1a for a schematic overview of the process [1]. When characterized via 2DSI, the pulse duration retrieved at the end of the fiber assembly was 10 fs at FWHM, with a 6 fs transform limited pulse, as shown by the red and blue traces in fig. 1c. The retrieved phase indicates that the pulse self-compresses to 6.8 fs 20 cm after the fiber assembly output (due to propagation through air), see the black trace in fig. 1c . Current efforts are focused on cleaning up the mode generated by the 3^rd harmonic arm, fig. 1a inset, to improve HCF coupling efficiency. The characterization of even shorter UV pulses with transform-limited duration below 2 fs is on-going, as well as the effort to scale up the pulse energy to few tens of µJ.

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