Large Capture Range Research Articles

Development of a broadband laser in the UV region

A frequency comb in the UV region with a bandwidth greater than 100 MHz is generated by successive frequency shifts of a single mode laser by an acousto-optic modulator coupled to a passive ring cavity. The obtained spectrum is particularly suitable for laser cooling when a large velocity capture range is required as in the case, for example, of ions confined in a storage ring.

Snakes, shapes, and gradient vector flow

Snakes, or active contours, are used extensively in computer vision and image processing applications, particularly to locate object boundaries. Problems associated with initialization and poor convergence to boundary concavities, however, have limited their utility. This paper presents a new external force for active contours, largely solving both problems. This external force, which we call gradient vector flow (GVF), is computed as a diffusion of the gradient vectors of a gray-level or binary edge map derived from the image. It differs fundamentally from traditional snake external forces in that it cannot be written as the negative gradient of a potential function, and the corresponding snake is formulated directly from a force balance condition rather than a variational formulation. Using several two-dimensional (2-D) examples and one three-dimensional (3-D) example, we show that GVF has a large capture range and is able to move snakes into boundary concavities.

Sharp edge broad-band lasers for "white-light" cooling in storage rings

We have developed broad-band laser sources which show a sharp edge in their spectra and are particularly suitable for ``white-laser'' cooling of ions in storage rings. They allow for a very large velocity capture range by maintaining the same cooling rate allowed by the single mode lasers. A large fraction of the circulating ions are expected to be cooled both in coasting and bunched beams. The device, which does not use an active medium, can easily operate at any frequency from UV to IR spectral region.

Generation of a frequency comb with a sharp edge of adjustable intensity and frequency

A frequency comb is generated by successive frequency shifts of a single mode laser by an acousto-optic modulator coupled to a passive ring cavity. The cavity design and the laser-cavity coupling have a very high efficiency and allow for a perfect control of both the frequency and the intensity of the sharp edge. A second acousto-optic modulator can be used to double the comb bandwidth. The obtained spectrum is particularly suitable for laser cooling when a large velocity capture range is required as it is the case, for example, of ions confined in a storage ring.

Transverse laser cooling of ions in a storage ring

We propose a method for a direct transverse laser cooling of ions in a storage ring and we discuss its application to 7Li + and 24Mg + ions studied in present storage rings. The key idea consists in the use of a broad-band laser, which, impinging transversely on the ion beam to be cooled, causes phase-space compression through resonance radiation pressure. Our technique, by allowing simultaneous resonant excitation of almost all ions regardless of their velocity, compensates for the short laser-ion interaction time and gives a very large capture range.

A simple frequency discriminator circuit for offset locking of lasers

Describes a frequency-lock circuit. The components used are readily available and the circuit can be easily reproduced. The design gives a fast loop response and large capture range, thus making it ideal for locking potentially noisy laser systems. In addition it is free from the problems of drift often associated with frequency-locked circuits. The authors have used the design to offset-lock two carbon dioxide lasers giving a resultant beat note only 500 Hz wide. The quality of the lock is independent of the size of the offset while the technique is adaptable to lasers in all parts of the spectrum, being limited only by the response of a suitable beat detector.

A CMOS analog continuous-time delay line with adaptive delay-time control

A CMOS analog continuous-time delay line composed of cascaded first-order current-domain all-pass sections is discussed. Each all-pass section consists of CMOS transistors and a single capacitor. The operation is based on the square-law characteristic of an MOS transistor in saturation. The delay time per section can either be controlled by an external voltage or locked to an external reference frequency by means of a control system which features a large capture range. Experimental verification has been performed on two setups: an integrated cascade of 26 identical all-pass sections and a frequency-locking system breadboard built around two identical on-chip all-pass sections. >

An exponential voltage-controlled oscillator improves the performance of a phase-locked loop

A design example is worked out to demonstrate how to stabilize a phase-locked loop containing an exponential voltage-controlled oscillator. It is shown that this kind of loop can be designed with an arbitrarily large capture range, a wide lock-in range, and a short transient receovery-time constant.