John M. J. Madey

Stimulated Emission of Bremsstrahlung in a Periodic Magnetic Field

The Weizsacker‐Williams method is used to calculate the gain due to the induced emission of radiation into a single electromagnetic mode parallel to the motion of a relativistic electron through a periodic transverse dc magnetic field. Finite gain is available from the far‐infrared through the visible region raising the possibility of continuously tunable amplifiers and oscillators at these frequencies with the further possibility of partially coherent radiation sources in the ultraviolet and x‐ray regions to beyond 10 keV. Several numerical examples are considered.

Relationship between mean radiated energy, mean squared radiated energy and spontaneous power spectrum in a power series expansion of the equations of motion in a free-electron laser

SummaryTo lowest order in the electric field and the inverse electron energy, the classical mean energy radiated by electrons in a free-electron laser with a symmetric magnet is equal to one-half the derivative, with respect to energy, of the classical mean squared radiated energy. The integral for the mean squared energy is also shown to be identical to the integral for the classical spontaneous power spectrum.RiassuntoPer l’ordine inferiore nel campo elettrico e per energia elettronica inversa, l’energia media classica emessa dagli elettroni in un laser a elettroni liberi con un magnete simmetrico è uguale a metà della derivata, rispetto all’energia, dell’energia irradiata quadratica media classica. Si è mostrato anche che l’integrale per l’energia media quadratica è identica all’integrale per lo spettro classico di potenza spontaneo.РезюмеВ низщем порядке по электрическому полю и обратной величине энергии электрона классическая средняя знергия, излучаемая электронами в свободном электронном лазере с симметричным магнитом, равна половине производной по знергии от классической среднадратичной излучаемой энергии. Показывается, что интеграл для среднеквадратичной энергии является идентичным интегралу для классического спонтанного степенного спектра.

The Stanford Mark III infrared free electron laser

Abstract We have built and operated a compact infrared free electron laser using a conventional linear accelerator and a broadband optical cavity. The gain was measured to be 28% and saturation was obtained with a 2.5 μs macropulse. The laser was tuned from 3.1 to 2.6 μm by changing the undulator gap. Coherent spontaneous radiation at the fifth and seventh harmonics was seen.

A Free Electron Laser

This paper includes a brief review of the theory of stimulated bremsstrahlung by relativistic electrons in a periodic magnetic field, a discussion of the possibilities for a classical interpretation, and a description of the apparatus under construction in W. W. Hansen Laboratories of Physics.

A free electron laser-photoemission electron microscope system (FEL-PEEM)

We report first results from our effort to couple a high resolution photoemission electron microscope (PEEM) to the OK-4 ultraviolet free electron laser at Duke University (OK-4/Duke UV FEL). The OK-4/Duke UV FEL is a high intensity source of tunable monochromatic photons in the 3–10 eV energy range. This tunability is unique and allows us to operate near the photoemission threshold of any samples and thus maximize sample contrast while keeping chromatic berrations in the PEEM minimal. We have recorded first images from a variety of samples using spontaneous radiation from the OK-4/ Duke UV FEL in the photon energy range of 4.0–6.5 eV. Due to different photothreshold emission from different sample areas, emission from these areas could be turned on (or off) selectively. We have also observed relative intensity reversal with changes in photon energy which are interpreted as density-of-state contrast. Usable image quality has been achieved, even though the output power of the FEL in spontaneous emission mode was several orders of magnitude lower than the anticipated full laser power. The PEEM has achieved a spatial resolution of 12 nm.

Reducing the sensitivity of a free‐electron laser to electron energy

A technique is described which allows a free‐electron laser to utilize an electron beam with a wide energy spread. A laser using this technique can be powered by a greater variety of electron sources than would otherwise be possible. In addition, the techniques ease some of the problems encountered when designing a laser to operate in conjunction with a storage ring.

Status report on the Stanford Mark III infrared free electron laser

Abstract We review recent experimental results from the Stanford Mark III infrared FEL. More than 900 h of lasing operation have achieved from 2.0 to 5.5 μm and continuous gap tuning has been achieved over the design range of 1.7:1. Micropulses with peak powers as high as 2 MW and pulse lengths as short as 500 fs have been measured. A multiple output coupler arrangement has been tested which allows variation of the output coupling from 0.1% to 7% in a matter of a few minutes. Accelerator performance will also be discussed and the results of recent improvements to the microwave gun will be presented. The measured brightness of this gun is in excess of 10 12 A/cm 2 which is sufficient for operation in the UV.

Superconducting helically wound magnet for the free‐electron laser

Theoretical and experimental studies conducted by the Stanford Free Electron Laser group have resulted in the first operation of a free-electron laser amplifier and free-electron laser oscillator. Two superconducting helically wound periodic magnetics have been constructed for use with the laser. In this paper we present a discussion of design considerations and test results for the two magnets. The tests included measurement of the magnitude and the variation of the transverse magnetic field with radius in the bore of the magnets, the critical current, and the intensity, angular distribution, and spectrum of the spontaneous radiation emitted by electrons moving through the field.

A review of the Stanford Mark III infrared FEL program

Abstract The performance of the Mark III infrared FEL with a new microwave gun will be reviewed. Operation of the accelerator is now close to design values. The Mark III has provided over 2000 hours of laser time to experiments in FEL physics, materials science and medical physics. Highlights of the experimental program will be presented and the new facility at Duke will be described.

Giant laser pulses in the Duke storage ring UV FEL

Abstract We have studied the dynamics of giant pulse generation in the Duke UV FEL with peak power of several gigawatts. The giant pulses will be provided by a FEL gain modulation technique developed for the OK-4 UV FEL at Novosibirsk, Russia. A new mechanism for “super-pulse” generation was discovered during these studies. It allows the generation of peak power up to 10 GW using the “phase space” refreshment of the electron beam caused by synchrotron motion [V. Litvinenko et al., to be published]. We have developed a new macro-particle code for giant pulse simulation including all known mechanisms of storage ring FEL interaction. Results of these giant pulse simulations are presented in the paper.