Page 505 - Tunable Lasers Handbook

9 Tunable Free-Electron Lasers 465
beamline. The user facility is now an international user facility and will provide
increased user time and more facilities for the users.

5.4 Princeton/Northrop-Grumman [3 1 ]
This compact facility, being constructed by Northrop-Grumman at Prince-
ton University, is designed to provide operation in the wavelength range of 5 to
15 pm 1vithL high-energy micropulses produced at 142.8 MHz. Initial operation
should be in the long-wavelength end of the design range since they are using a
permanent magnet wiggler from LANL. Later operation will use an 8-mm
period superferric undulator developed in collaboration with BNL. This will
allow operation down to the shortest wavelengths in the range. The facility will
be a university-based user facility rather than a national user facility.

5.5 Stanford University [55]

This user facility uses a superconducting accelerator to provide lasing in the
infrared from 3 to 15 pm with very long macropulses of several milliseconds and
a large separation between micropulses of 84.6 ns. The macropulses can occur at
up to 120 Hz. The long separation between micropulses allows for samples to
cool or relax between pulses and also allows the use of acousto-optic or electro-
optic witches to pick out single pulses with good contrast. The microbunches
have typically about 0.1 to 1 pJ of energy so the power in the laser beam delivered
to the lab is on the order of 1 to 10 W during the macropulse. The micropulse
length can be varied from one to several picoseconds in length so the peak power
is from 0.1 to 1 MW during the micropulses. The facility has three operational
lasers, with one operating in the near infrared from 3 to 8 pm, the second operat-
ing in the mid-infrared region from 5 to 15 pm. and the third operating in the far-
infrared region from 18 to 64 pm.
The spectral bandwidths range from 0.1 to 1%) FWHM. Due LO a rather low
gain. the laser must usually operate with dielectric optics so the user is generally
limited to the wavelength range of the set of mirrors for the length of a shift. The
mirrors cain be changed in a couple of hours to change the wavelength range.
The wavelength is changed by changing the electron beam energy.
The unique features of the Stanford facility include the following:
1. The wavelength is extremely stable. Using feedback techniques, it is
possible to hold the wavelength stable to 0.01% over hours. The user
can vary the wavelength over several percent using a single knob.
2. The wavelength can be slewed by several percent during the
macropulse in any pattern the user desires. This may be useful in
some vibrational studies.