The electromagnetic-wiggler harmonic amplifier FEL

Abstract

Abstract In this paper, we present a variation of the two-stage FEL based on the HARmonic amPlifier FEL (HARP/FEL) [1,2] called the electromagnetic-wiggler HARP/FEL (EHARP). In the EHARP, the first stage is a conventional magnetic-wiggler FEL while the second stage's wiggler is an electromagnetic standing wave that is formed within the first stage's optical resonator by pumping with a microwave source. This two-stage FEL approach differs from that proposed by Elias [3] in that the first stage is not used to pump the second stage's optical wiggler; rather, its funtion is to enhance the second stage's gain by appropriately modulating the electron beam as it passes through the device. Such modulation occurs when the pump frequency is chosen such that the ratio of the bunching wavenumbers for the stages is a small integer. The advantage of the EHARP scheme is that the second stage does not need to reach laser threshold in order to radiate and its power is linear in the pump power. We compute the requirements of emission for an EHARP design based on the UCSB-FEL system where the first stage lases at wavelengths from 100 to 160 μm and the secons stage emits at a multiple of the first stage frequency. We predict that the two-stage mechanism may be demonstrated with an existing microwave device (such as the Hughes Mark-II FEL) for the pump source.