Observation of coherently enhanced tunable narrow-band terahertz transition radiation from a relativistic sub-picosecond electron bunch train

Abstract

We experimentally demonstrate the production of narrow-band (df =f % 20% at f % 0:5 THz) transition radiation with tunable frequency over [0.37, 0.86] THz. The radiation is produced as a train of sub-picosecond relativistic electron bunches transits at the vacuum-aluminum interface of an aluminum converter screen. The bunch train is generated via a transverse-to-longitudinal phase space exchange technique. We also show a possible application of modulated beams to extend the dynamical range of a popular bunch length diagnostic technique based on the spectral analysis of coherent radiation.

Characterization of the THz radiation source at the Frascati linear accelerator

“…Recently, it has been demonstrated that it is possible to generate tunable, narrowband, few-cycle, and multicycle coherent THz radiation by properly shaping the longitudinal charge distribution of the electron beam. Different approaches are currently used: a temporally shaped photocathode drive laser pulse, 16, 17 a mask in a high dispersion, low beta function region of a beamline dogleg in order to produce a temporal bunch train out of a long bunch with a correlated energy spread, 18 a transversely segmented beam (with a multislit mask) manipulated via a transverse-to-longitudinal phase space exchange technique, 19 and an ultra-short relativistic electron bunch passing through a magnetic undulator. 20 For instance, molecular spectroscopy and imaging can benefit from a high peak power, tunable THz radiation with narrow spectral bandwidth.…”

Non-destructive measurement and monitoring of separation of charged particle micro-bunches

“…On the other hand, to enable the THz radiation source tunability and its stable operation, 1-5 the accurate knowledge of the distance between bunches is also required, as the spacing between micro-bunches defines the spectrum of the radiation. [18][19][20][21][22][23][24] In both examples and in other applications driven by such beams, the development of a non-invasive, a single-shot system capable of monitoring the distance between micro-bunches is important, and in many cases, non-destructive, single-shot evaluation of the bunch-to-bunch distance is still an unresolved challenge. At present, the most popular techniques used to study micro-bunch separations are via measurements of autocorrelation functions 2,18,19 and use of a transverse deflection cavity.…”

“…At present, the micro-bunched beam can be generated by a beam in the following techniques: modulation in a plasma channel, 6-8,10-12 "slicing," 2,3,18 seeded instability, 4,13,14 and directly from a photocathode. 5,19,25,26 In all of these techniques, the final spacing between micro-bunches can vary from shot to shot. Here (for reasons of clarity only), we will focus on the generation of the micro-bunches directly from a photocathode.…”

Passive longitudinal-phase-space tailoring of non-ultrarelativistic beams with dielectric-lined waveguides

“…Possible methods include the use of a shaped mask in a dispervise section [15,16], the mapping of a transversely-shaped beam into the temporal axis using a transverse-to-longitudinal phase-space exchanger [17] or the use of nonlinear longitudinal manipulation [18,19]. Here we point out that the passive technique described in the this paper can be used to form beams with tailored current profiles.…”