Eric B. Szarmes

Generation of Bessel beams using a 4-f spatial filtering system

We demonstrate a simple and straightforward method of producing Bessel beams using a 4-f spatial filtering system that requires no specialized optical components. The experiment employs the established technique of diffraction from a thin ring source, but the ring source is produced by the high-pass filtering of a uniformly illuminated circular aperture, yielding Bessel beams with a central spot radius of less than 35μm which persist over a distance of 160mm. The experiment unifies diffraction theory, Fourier optics, and the properties of Bessel beams in a manner appropriate for an advanced undergraduate laboratory.

Use of inverse tapering to optimize efficiency and suppress energy spread in an RF-linac free-electron laser oscillator

We have studied the operation of tapered undulator free-electron lasers using a realistic numerical model which accurately accounts for short-pulse effects, mode pulling, and coupled electron-optical beam instabilities. Our simulations are based on the Maxwell-Lorentz equations of motion, incorporating realistic optical resonator modes and electron density fluctuations, and accurately track the phase and energy of the electrons throughout their entire interaction with the optical pulse. The studies assume a 2-m taperable undulator with a normalized vector potential of roughly unity, driven by an electron beam from either a thermionic or photocathode microwave gun. Inverse tapering was found to provide greater extraction efficiency and optical power than conventional tapering in moderate gain systems using thermionic injector technology, and yielded over four times the extraction efficiency of an untapered undulator with minimal effect on the energy spread of the electron beam. In contrast, little improvement in efficiency or power output was observed using a photocathode injector due to loss of coherence at high gain. The remarkable spectral stability, laser power output, and reduced energy spread achievable using inverse tapering in moderate gain systems are discussed with respect to applications in remote sensing and spectroscopy.

Van de Graaf-based 13.5 nm inverse-Compton light source

We review the factors governing the performance of inverse-Compton light sources in the extreme-ultraviolet (EUV) region. While the use of an optical storage cavity and the minimization of the laser pump focal spot area remain critical to the optimization of power and brightness in the EUV, the appearance of a strong space charge forces at the low electron energies required for operation in the EUV sets an independent lower limit to the focal spot area, and therefore an upper limit to source power and brightness. These limitations are at least partially compensated by the very high average electron currents realizable at these lower electron energies. Based on these considerations, we describe the design and estimated performance of an EUV inverse-Compton scattering light source optimized for average power output and brightness consistent with the limits imposed by the capabilities of existing materials, laser pumps, and radio frequency power sources.

Remote sensing applications of a free-electron laser lidar

A high average power and high spectral brightness free-electron laser (FEL) being developed at the University of Hawaii as a lidar transmitter for atmospheric and oceanic research. The FEL will be tunable from the UV to the mid-infrared. Peak power in the picosecond long micropulses of the FEL will reach 10 s of MW, and these will average to the order of 100 kW over the 5 microsecond long macropulses. The repetition rate of the micropulses will be in the range 1 to 3 GHz during one macropulse, and the macropulses will repeat at 180 Hz. The unique pulse structure of the FEL output with high pulse power will allow exploitation of non-linear optical spectroscopic techniques for identifying various types of aerosols and pollutants in the atmosphere. The wide tunable range in the mid-IR region will allow sensitive detection of chemical species by operating the FEL transmitter in the differential absorption lidar (DIAL) mode, and the high spectral brightness will allow unprecedented signal-to-noise ratio.

Broadband tunable scanning IR-range etalon for FEL applications

A broadband, tunable, scanning IR-range etlon for FEL applications was designed, developed and tested. The design details and the results of the experimental tests are described and discussed.