High-resolution free-electron laser spectroscopy

Thesis/Dissertation · Wed Jan 01 04:00:00 EST 1992

OSTI ID:6886379

Szarmes, E B

The broad and continuous turnability of the rf linac-driven free-electron laser (FEL), coupled with its high power picosecond time structure, has greatly enhanced the research capabilities in the field of infrared spectroscopy. However, the duration of the optical pulses is often too long to probe ultrafast processes, and the spectral structure of the optical beam, with closely spaced longitudinal modes in a bandwidth determined by the Fourier transform of the short pulses, poses a significant limitation for experiments requiring high spectral resolution. The temporal resolution can be improved by operating the FEL with electron pulses whose energy varies linearly with time; the resulting optical pulses possess substantial frequency chirps and are susceptible to pulse compression in an external dispersive delay line. The spectral resolution can be enhanced by using an intracavity Michelson interferometer to couple successive optical pulses so that they build up from noise with a definite phase relationship; the longitudinal modes in the output beam are then separated by the rf frequency of the linac and can be individually filtered for applications in high resolution spectroscopy. This dissertation develops small signal analyses for each of these modes of operation, and reports the results of numerical pulse propagation simulations whose parameters were chosen to guide the design of feasible experiments on the Mark III FEL. Chirp-pulse simulations using modest energy chirps have demonstrated a x15 compression ratio at saturated power levels for 3.4 ps optical pulses at 3.35 [mu]m, and coupled pulse simulations have indicated substantial longitudinal mode reduction on microsecond time scales. The author also developed a derivation of FEL coupled mode equations using conventional mode locked laser theory, and solved them numerically in the frequency domain. Finally, the author reports the first operation of a Michelson mirror resonator on the Mark III FEL.

• Research Organization: Stanford Univ., CA (United States)
• OSTI ID: 6886379
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400102* -- Chemical & Spectral Procedures
440600 -- Optical Instrumentation-- (1990-)
47 OTHER INSTRUMENTATION
CONTROL
ELECTROMAGNETIC PULSES
ELECTROMAGNETIC RADIATION
EXPERIMENT PLANNING
FREE ELECTRON LASERS
FREQUENCY CONTROL
INFRARED SPECTROMETERS
INTERFEROMETERS
LASER SPECTROSCOPY
LASERS
MEASURING INSTRUMENTS
MICHELSON INTERFEROMETER
PLANNING
PULSES
RADIATIONS
RESOLUTION
SPECTROMETERS
SPECTROSCOPY