• C.H. Chen, K.Y. Huang, Y.-C. Huang
  NTHU, Hsinchu
• W.K. Lau, A.P. Lee
  NSRRC, Hsinchu

A THz-pulse-train pho­toin­jec­tor is under con­struc­tion at the High-en­er­gy OP­tics and Elec­tron­ics (HOPE) Lab. at Na­tion­al Ts­inghua Uni­ver­si­ty, Tai­wan. This pho­toin­jec­tor is be­lieved to be use­ful for gen­er­at­ing high-pow­er THz ra­di­a­tion, as well as for driv­ing or load­ing a plas­ma-wave ac­cel­er­a­tor. A THz laser beat wave with full tun­abil­i­ty in its beat fre­quen­cy is em­ployed to in­duce the emis­sion of the THz elec­tron puls­es from the pho­toin­jec­tor. We show in our study that such a pho­toin­jec­tor is ca­pa­ble of gen­er­at­ing pe­ri­od­i­cal­ly bunched MeV elec­trons with a bunch­ing fac­tor larg­er than 0.1 at THz fre­quen­cies for a total amount of 1nC charges in a 10-ps time du­ra­tion. We will also pre­sent a driv­er laser tech­nol­o­gy that can tune the elec­tron bunch fre­quen­cy with ease and help the growth of the high har­mon­ics in the bunch­ing spec­trum of ac­cel­er­at­ed elec­trons. Ex­per­i­men­tal progress on this pho­toin­jec­tor will be re­port­ed in the con­fer­ence. The au­thors grate­ful­ly ac­knowl­edge fund­ing sup­ports from Na­tion­al Sci­enc Coun­cil under Con­tract NSC 97-2112-M-007-018 -MY2, Na­tion­al Syn­chrotron Ra­di­a­tion Re­search Cen­ter under Pro­ject 955L­R­F01N, and Na­tion­al Ts­inghua Uni­ver­si­ty under Pro­ject 98N2534·10¹.

• Y.-C. Huang, C.H. Chen
  NTHU, Hsinchu

We study a desk­top MW su­per­ra­di­ance free-elec­tron laser (FEL) at THz fre­quen­cies. By using some nom­i­nal beam pa­ram­e­ters from a THz-pulse-train elec­tron gun, we show in the­o­ry and sim­u­la­tion that 10-MW-lev­el ra­di­a­tion power at THz fre­quen­cies is achiev­able from a meter long un­du­la­tor in one sin­gle elec­tron tran­sit through the un­du­la­tor. The pro­posed THz su­per­ra­di­ance FEL is di­rect­ly at­tached to the emit­tance com­pen­sat­ing coil of the pho­toin­jec­tor with­out using any ad­di­tion­al beam-fu­cus­ing el­e­ment in be­tween. This com­pact de­sign al­lows the con­struc­tion of a 10-MW FEL at THz fre­quen­cies on an or­di­nary desk. We will also show the use­ful­ness of a ta­pered un­du­la­tor for a su­per­ra­di­ance FEL. With a 20% lin­ear­ly ta­pered un­du­la­tor, the FEL ra­di­a­tion power can be in­creased by more than 30%. This FEL is being con­struct­ed at the High-en­er­gy OP­tics and Elec­tron­ics (HOPE) Lab­o­ra­to­ry, Na­tion­al Ts­inghua Uni­ver­si­ty, Tai­wan. Ex­per­i­men­tal progress of this ul­tra­com­pact, high-pow­er sin­gle-pass su­per­ra­di­ance FEL will be re­port­ed in the con­fer­ence.