Update on FELIX

Amersfoort, P.W. van; Bakker, R.J.; Bekkers, J.B.; Best, R.W.B.; Buuren, R. van; Delmee, P.F.M.; Faatz, B.; Geer, C.A.J. van der; Hellingman, P.; Jaroszynski, D. A.; Manintveld, P.; Mastop, W.J.; Meddens, B.J.H.; Meer, A. F. G. van der; Nijman, Jint; Oepts, D.; Pluygers, J.; Wang, Wei; Wiel, M.J. van der

doi:10.1016/0168-9002(91)90841-d

Cited by 10 publications

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“…In this paper we present the first experimental demonstration of phase-locked operation in the free-electron laser for infrared experiments (FELIX) [5]. This laser uses an rf linear accelerator with a micropulse repetition frequency of 1 GHz to permit harmonic mode locking.…”

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confidence: 99%

Induced and spontaneous interpulse phase locking in a free-electron laser

et al. 1992

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We present the first experimental demonstration of phase locking between successive optical micropulses in a free-electron laser in which the electron pulses are separated by a fraction of the opticalcavity round-trip time. A Fox-Smith interferometer arrangement has been used to induce a high degree of interpulse phase coherence. Surprisingly, a substantial amount of coherence has also been observed without the phase-locking arrangement. A tentative explanation of this phenomenon is given. PACS numbers: 41.60.Cr, 42.60.Fc, 42.72.AiThe free-electron laser (FEL) is a valuable tool for fundamental research in physics and chemistry. Especially in the infrared to far-infrared spectral regions, where no other powerful tunable lasers are available, many new applications are possible [1], A radio-frequency (rf) accelerator is commonly used as the source of the electrons in an FEL, except for submillimeter wave generation, where an electrostatic accelerator can provide sufficiently energetic electrons. An rf accelerator produces an electron beam in the form of macropulses with a duration in the microsecond range, each consisting of micropulses with a duration in the picosecond range. In most existing FELs, the interval between micropulses equals one optical-cavity round-trip time. As a result, the laser operates as a synchronously pumped mode-locked laser. This is very useful for applications of the FEL in studies of fast dynamical processes and nonlinear effects. On the other hand, the linewidth of such a laser is broad due to the short duration of the micropulses, which prohibits its use in high-resolution work, where long-range coherence is required. There is, of course, coherence over multiples of the optical-cavity round-trip time, as in any laser oscillator, and the spectrum consists of discrete cavity modes, each with a width much smaller than the full laser bandwidth. However, as the optical-cavity length of an FEL normally amounts to several meters, the mode spacing is very small, and external selection of a single mode is virtually impossible. In addition, each mode contains only a very small fraction of the total power, because the number of modes contributing to the pulse essentially equals the ratio of the round-trip time to the micropulse duration. It is not possible to make such a laser operate in a single axial mode due to the efficient mode locking effected by the short electron pulses.

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confidence: 99%