A theoretical and experimental investigation of the operation of a harmonic gyrotron at submillimeter wavelengths is reported. Using a waveguide cavity with an iris at the output end of the straight section, 14 different second-harmonic modes were observed with frequencies of 301-503 GHz, output powers of 1-22 kW, and a 12-MHz emission frequency bandwidth. The highest output power was 22 kW, with a total efficiency of 3.5% at 467 GHz, and an output power of 15 kW with a 6% efficiency was obtained at 417 GHz. Research was conducted using a 65-75 kV up to 10-A electron gun with a 1/1.5- mu s pulse length and a 4-Hz repetition rate, which produced a helical electron beam in magnetic fields of up to 14 T. These results represent the first operation of a high-power harmonic gyrotron in the submillimeter region. >

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Submillimeter-wave harmonic gyrotron experiment

Matrix-assisted laser desorption and ionization in the OH and CO absorption bands of aliphatic and aromatic matrices: dependence on laser wavelength and temporal beam profile

We describe a new method for etching patterns in silver, copper, or gold, or other plate metal thin films. A pattern of a hard mask is placed onto the surface of the thin film, followed by a step of reactive ion etching using a plasma formed using a gas feed of some combination of some amounts of methane (CH 4 ) and hydrogen (H 2 ), and some or no amount of Argon (Ar). The areas of silver, copper or gold not covered by the hard mask are etched while the hard mask protects those areas that will form the raised portions of thin film in the final structure.

Patterning thin metal films by dry reactive ion etching

A method is disclosed for irradiating a biological sample with far infrared (FIR) irradiation, including providing tunable FIR irradiation, removing X rays from the irradiation, and irradiating at least one biological sample with the tunable FIR irradiation, wherein at least a component of the biological sample undergoes at least one of a conformational change or a phase change in response to the irradiating. An FIR irradiation device is disclosed, including an FIR source producing an FIR irradiation having a tunable wavelength, the source being capable of continuous-wave output, and a filter receiving the irradiation from the source.

Applying far infrared radiation to biological matter

A device couples energy from an electromagnetic wave to charged particles in a beam. The device includes a micro-resonant structure and a cathode for providing electrons along a path. The micro-resonant structure, on receiving the electromagnetic wave, generates a varying field in a space including a portion of the path. Electrons are deflected or angularly modulated to a second path.

Structures and methods for coupling energy from an electromagnetic wave

The invention envisages control devices acting on the laser to vary in time the electron/photon interaction, means proceeding to a State I in which they alter the optimal conditions for laser amplification; and a State II in which that reestablish said optimal conditions, which control devices permit the improvement of the peak amplitude and stability of the laser pulses and the rate and stability of the pulse period. According to another aspect of this invention, the two states are alternated, preferably periodically or almost periodically. The duration of State I should be selected by comparison with the characteristics of the electron packet and, in particular of the relaxation time observed for said packet. If the duration of State II is set to a value to be comparable to or longer than the electron relaxation time, the peak amplitude of the laser pulses is increased. The duration of State II should be selected by comparison with the natural macropulse width. If the duration of the State II is set to a value shorter than the natural duration of the laser macropulses, the repetition rate of the laser pulses can be increased.

Free electron laser

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.

The Stanford Mark III infrared free electron laser

Following the first storage ring Free Electron Laser (FEL) acheived between 1983 and 1986 in the visible on ACO, new experiments are under developpment on the new ring Super-ACO for extending the radiation from the visible to the UV and VUV ranges. For FEL experiments, Super-ACO is operated at 600MeV, with two stabilized opposite bunches, separated by 120ns. The permanent magnet optical klystron consists in two undulators of 10 periods of 13cm each, and a 0.5m long dispersive section in the middle, with a maximum deflection parameter K value of 5.75. The 18m long optical cavity and the mirrors were set-up at the end of January. A specific "low emittance" optics provides 2% of gain at 600MeV. The laser oscillation was acheived on Super-ACO in February at 633nm with 2A of bandwidth. Tunability results from the undulators gap change. The FEL remains down to 3mA per bunch. Except from the microtemporal structure due to the storage Ring, the macrotemporal structure seems to be continuous, showing the high stability of the positron beam.

Status of the free-electron laser experiment on the Super-ACO storage ring

Les quelques observations signalees dans la litterature montrent qu'une impulsion Laser induit dans divers milieux materiels tels que l'air, l'eau, les solides cristallins (par exemple quartz), ou au contraire amorphes (par exemple plexiglas), egalement dans divers milieux biologiques, des vibrations acoustiques dans une large gamme de frequences. Nos experiences montrent qu'il est possible d'exploiter cet effet en vue d'une nouvelle methode de demodulation d'un faisceau Laser par des couches minces de sulfure de cadmium ayant la particularite de fournir une tension piezoelectrique avec un temps de reponse comparable a celui obtenu avec des photodiodes au silicium. Ce nouveau procede de detection permet de demoduler un faisceau Laser sans perturber sa propagation, le prelevement d'energie s'effectuant par l'intermediaire des vibrations acoustiques induites dans les milieux materiels dans lesquels le faisceau se propage.

https://hal.archives-ouvertes.fr/jpa-00205975/document

Quelques expériences relatant l'induction d'ondes acoustiques dans divers milieux matériels traversés par ou ayant subi l'impact d'impulsions laser

Le laser est constitue d'un anneau de stockage (1) dont une section en liqne droite (18) est equipee d'un onduleur (2). Deux miroirs (M31 et M32) definissent une cavite optique (3) coaxiale a l'onduleur (2). En agissant sur une cavite hyperfrequence (5) de l'anneau de stockage, on peut controler dans le temps l'interaction electrons/photons, et ameliorer par la l'amplitude de crete des impulsions laser et/ou les taux de repetition ainsi que leurs stabilites.

Michel Velghe

Papers

Free electron laser

The Stanford Mark III infrared free electron laser

Status of the free-electron laser experiment on the Super-ACO storage ring

Quelques expériences relatant l'induction d'ondes acoustiques dans divers milieux matériels traversés par ou ayant subi l'impact d'impulsions laser

Laser à électrons libres perfectionné