We present the results of a proof-of-principle experiment to demonstrate the generation of tunable radiation from a laser-ionized gas-filled capacitor array. This scheme directly converts a static electric field of wave number k 0 into coherent radiation pulses of frequency v 2 p ͞2k 0 c, where v p is the plasma frequency. The radiation frequency can be tuned by varying gas pressure and /or capacitor spacing. In this experiment, well-polarized, short (less than 5 ns) microwave pulses have been generated over a frequency range of 6 to 21 GHz. The frequency of the detected signal, as measured with cutoff waveguides, scales linearly with the plasma density, and the relative power of the signal scales quadratically with the dc bias voltage in agreement with the theory. [S0031-9007(96)01789-9]

The dc to ac radiation converter is a new device in which a relativistic ionization front directly converts the static electric field of an array of alternatively biased capacitors into a pulse of tunable radiation. In a proof-of-principle experiment frequencies between 6 and 21 GHz were generated with plasma densities in the 10 12 cm Ϫ3 range and a capacitor period 2dϭ9.4 cm. In the present experiment, short pulses with frequencies between 39 and 84 GHz are generated in a structure with 2dϭ2 cm. The frequency spectra of these pulses are measured using a diffraction grating. The spectra are discrete, and their center frequency varies linearly with the gas pressure prior to ionization ͑or plasma density͒, as expected from theory. Their relative spectral width is around 18%, consistent with the expected number of cycles ͑six͒ contained in the pulses. An upper limit of 750 psec ͑bandwidth detection limited͒ is placed on the pulses length. The emitted frequency increases from 53 to 93 GHz when the capacitors are connected by pair to obtain a effective array period of 4 cm.

No abstract

The output radiation of a dc to ac radiation converter is characterized. A relativistic ionization front passing through a capacitor array of period dϭ1 cm produces short pulses of tunable radiation between 39 and 84 GHz with a gas pressure between 0 and 30 mT. The frequency spectra of the produced pulses are discrete and exhibit full widths at half maximum between 12% and 28%, consistent with the expected width for six cycles' pulses. An upper bound of 750 ps ͑detection bandwidth limited͒ is placed on the pulse widths. These are the shortest pulses produced by a source of coherent radiation in this frequency range.

Experimental observation of pulsed radiation ranging from ∼20 GHz to above 100 GHz during the hollow cathode discharge phase of operation of a back-lighted thyratron is reported. The discharge is operated with 120 mTorr Ar gas at 20 kV initial voltage. Pulsed radiation was observed for ∼50 ns, and an electron beam with energy of ∼20 keV was also observed. The observations are correlated with plasma processes predicted in recent computer simulations. The sudden turn-off of the radiation is believed to be a result of plasma expansion and sheath contraction inside the hollow cathode region. A method for varying the pulse length is discussed.

A variable pulse-length electron-beam source capable of 100’s μs pulse is reported. Long-pulse electron-beam generation was based on the hollow cathode discharge mode of operation of the back-lighted thyratron and achieved by the modification of circuit parameters that control the discharge. With 75 mTorr Ar and 20 kV applied voltage, the electron beam went through a transient phase before reaching a steady-state long-pulse generation. During the transient phase, a fast-decaying voltage (20–2 kV) and a pulse of 2.5 A and 130 ns FWHM electron beam were observed. The self-extracted long-pulse electron beam has a duration ∼100 μs, energy ∼2 keV, and current density ∼10 A/cm2. The results demonstrate the feasibility of controlling the electron-beam pulse length. The device is simple, robust, and compatible with a plasma environment.

We intend to carry out a series of plasma lens experiments at the Final Focus Test Beam facility at SLAC. These experiments will be the first to study the focusing of particle beams by plasma focusing &vices in the parameter regime of interest for high energy colliders, and is expected to lead to plasma lens designs capable of unprecedented spot sizes. Plasma focusing of positron beams will be attempted for the first time. We will study the effects of lens aberrations due to various lens imperfections. Several approaches will be applied to create the plasma required including laser ionization and beam ionization of a working gas. At an increased bunch population of 2.5x lOlo, tunneling ionization of a gas target by an electron beam -an effect which has never been observed before -should be significant. The compactness of our device should prove to be of interest for applications at the SLC and the next generation linear colliders.

Abstraci -The feasibility of measuring four profile parameters, i.e., total etch depth, critical dimension (CO), thickness of remaining poly hard mask, and sidewall angle, for the metal-0 trench of DRAM by a single technique was investigated in this study. Broad band spectroscopic ellipsometry was used to provide non-destructive profile information. The results prove its capability for providing the required profile information, traditionally measured on 4 different metrologV tools, by a single measurement. This capability could significantly simplih the process flow for metal-0 trench.