FEL2026 - 42nd International Free Electron Laser Conference

Studies on optical cavity misalignment effects in the IR-FEL at RRCAT, India

TUP34

25 Aug 2026, 16:00

2h

Poster Presentation Session 6: FEL Oscillators and Infrared FEL (IR-FEL) Tuesday Poster Session

Speaker

Sona Chandran P (Raja Ramanna Centre for Advanced Technology)

Description

The Infrared Free Electron Laser (IR-FEL) at the Raja Ramanna Centre for Advanced Technology (RRCAT) is the first operational FEL based user facility in India, delivering radiation in the wavelength range of 12.5-50 µm. At a repetition rate of 2 Hz, a CW average power >20 mW, micro-pulse peak power ~ 10 MW, micro-pulse energy ~100 µJ and peak spectral brightness up to ~10¹⁸ photons/s/mm²/mrad²/0.1%BW has been achieved at 21.8 µm wavelength^*,^**. Lasing characterization revealed lower round-trip cavity loss, a wider detuning curve, and higher sensitivity to downstream offset than that predicted by the simulations. To understand this, detailed studies on cavity alignment sensitivity and detuning behavior were conducted through experiments and FEL simulations using GENESIS-OPC^***. Simulations predict that a static upstream mirror tilt causes a reduced alignment tolerance and low cavity loss^****. Start-to-end simulations with a 6-D electron beam distribution predict that the longitudinal beam profile significantly affects the detuning behaviour. These studies provide a sensitive diagnostic tool for optical cavity alignment, thereby helping in the performance optimization of the IR-FEL.

Footnotes

• Sona Chandran et al., Characterization of the Infrared Free Electron Laser (IR-FEL) at RRCAT”, NIM A, 1084 (2026) 171214.
  ** M.K. Chattopadhyay, et al., Current Science, Vol. 128, No. 7, 10 April 2025.
  *** G. Karssenberg, V.J.M. Van der slot, GENESIS-OPC Manual Release 0.7.9, University of Twente, 2014.
  **** Sona Chandran, et al., Characterization of Lasing of the Infra-red Free Electron Laser at RRCAT.