12.3.1 A Condensed FEL History
Hard X-ray FELs have only appeared in the last decade, but they represent the
culmination of more than half a century of research. As far back as 1953, Motz used
an electron bunch length shorter than the radiation wavelength to observe coherent
radiation in the mm wavelength range from an undulator and a 5 MeV electron beam
[556]. In the early 1970s, Madey’s group demonstrated the FEL concept in the
infrared using using a 24 MeV electron beam [557, 558]. Once “Self-Amplified
Spontaneous Emission” or “SASE” theory was developed, it became clear that
mirror-free FELs were possible, and the next few decades saw a progression of
SASE demonstrations from 1 cm to 1 Å. The world now has five hard X-ray FELs
(Appendix Table M.1 and Fig. 12.8), doubtless with upgrades and additional sources
to come. More on the history of FEL development can be found in reviews by
Pellegrini [559, 560] and Madey [561].
A Selective History of FEL Highlights
1953—Motz observes coherent mm radiation from undulator [556]
1971–1973—Madey low-gain FEL theory [557, 558]
1976–1977—Madey demonstrates low-gain FEL at 10.6 μ [562, 563]
1980—Kondratenko and Saldin: High-gain SASE concept [564]
1984—Bonifacio, Pellegrini, and Narducci SASE theory [565]
1985—LBNL/Livermore SASE demonstration at 1 cm [566]
1998—UCLA/Los Alamos SASE demo at 12 μ [567]
2001—Argonne “LEUTL” SASE demonstration at 520 and 385 nm [568]
2002—DESY SASE at 98 nm [569]
2005—TESLA test facility (FLASH): Soft X-ray FEL at 32 and 4.2 nm [570]
2012–2016—FERMI HGHG seeded FELs: 65–20 nm to 4 nm [571]
2009—LCLS hard X-ray FEL at 1.5 Å [572]
2012—SACLA FEL at 0.6 Å [573]
2017—European XFEL: high repetition rate XFEL [574]
12.4 FEL Physics
Free-electron lasers offer enormous improvements in peak brightness. The fundamental mechanism behind the “FEL process” involves the interaction between the
electrons oscillating through an undulator and the synchrotron radiation that these
electrons produce. It is achieved by (1) using bunches that are three orders of
magnitude shorter, (2) achieving an ultralow electron beam emittance that creates
a diffraction limited source, and (3) having very long undulators that allow development of a microbunch structure on the overall bunch so that the electrons radiate
coherently.
12.4 FEL Physics
297
Hard X-ray FELs have only appeared in the last decade, but they represent the
culmination of more than half a century of research. As far back as 1953, Motz used
an electron bunch length shorter than the radiation wavelength to observe coherent
radiation in the mm wavelength range from an undulator and a 5 MeV electron beam
[556]. In the early 1970s, Madey’s group demonstrated the FEL concept in the
infrared using using a 24 MeV electron beam [557, 558]. Once “Self-Amplified
Spontaneous Emission” or “SASE” theory was developed, it became clear that
mirror-free FELs were possible, and the next few decades saw a progression of
SASE demonstrations from 1 cm to 1 Å. The world now has five hard X-ray FELs
(Appendix Table M.1 and Fig. 12.8), doubtless with upgrades and additional sources
to come. More on the history of FEL development can be found in reviews by
Pellegrini [559, 560] and Madey [561].
A Selective History of FEL Highlights
1953—Motz observes coherent mm radiation from undulator [556]
1971–1973—Madey low-gain FEL theory [557, 558]
1976–1977—Madey demonstrates low-gain FEL at 10.6 μ [562, 563]
1980—Kondratenko and Saldin: High-gain SASE concept [564]
1984—Bonifacio, Pellegrini, and Narducci SASE theory [565]
1985—LBNL/Livermore SASE demonstration at 1 cm [566]
1998—UCLA/Los Alamos SASE demo at 12 μ [567]
2001—Argonne “LEUTL” SASE demonstration at 520 and 385 nm [568]
2002—DESY SASE at 98 nm [569]
2005—TESLA test facility (FLASH): Soft X-ray FEL at 32 and 4.2 nm [570]
2012–2016—FERMI HGHG seeded FELs: 65–20 nm to 4 nm [571]
2009—LCLS hard X-ray FEL at 1.5 Å [572]
2012—SACLA FEL at 0.6 Å [573]
2017—European XFEL: high repetition rate XFEL [574]
12.4 FEL Physics
Free-electron lasers offer enormous improvements in peak brightness. The fundamental mechanism behind the “FEL process” involves the interaction between the
electrons oscillating through an undulator and the synchrotron radiation that these
electrons produce. It is achieved by (1) using bunches that are three orders of
magnitude shorter, (2) achieving an ultralow electron beam emittance that creates
a diffraction limited source, and (3) having very long undulators that allow development of a microbunch structure on the overall bunch so that the electrons radiate
coherently.
12.4 FEL Physics
297