Laser cavity for generation of variable-radius rings of light.

We report a laser cavity that has a ring as its output mode. The radius of the ring can be scanned by tuning the laser frequency. This design can be implemented in any tunable laser with large gain and can be useful when ring illumination patterns are needed. As an example, we demonstrate this new cavity configuration by using a side-pumped grazing-incidence dye laser.

Electromechanical analogs of human reflexes.

The conclusion to be drawn from our modeling is that the combined stretch and tendon reflexes alone can endow artificial muscle with a springlike feel as well as give it a baseline tone. In response to questions that motor physiologists often ask as to what variables the system controls, the answer here is clear: the stretch and tendon reflexes act together to maintain both a tension set-point and a length set-point, but in so doing they also give the system a springlike feel because of the existence of a servo error. The main goal of our studies is to understand the integration of reflexes, and thus far we have only begun to explore the two lowest-level spinal reflexes. We are in the process of expanding this work by developing a much more refined arm explicitly modeled after the human arm. This new arm is to be activated by a minimum of 10 muscles, each of which is reflexively driven, and it will allow us to explore the integration of higher-level reflex action such as automatic inhibition of antagonists and facilitation of synergists.

Novel geometry for single-mode scanning of tunable lasers.

We describe a geometry that allows for the single-mode scanning of lasers that use a diffraction grating as the dispersive element. It is observed that under the right conditions a rotation of the tuning element can provide changes simultaneously in cavity length and diffraction angle that exactly match the requirements needed for continuous single-mode scanning. As a case study, the method is applied to the grazing-incidence pulsed dye laser.

Single-mode operation of grazing-incidence pulsed dye laser.

A variation of the grazing-incidence pulsed dye laser is presented. This laser has been operated in a single longitudinal cavity mode with a single-shot linewidth of less than 300 MHz and a time-averaged linewidth of 750 MHz. The single-mode conversion efficiency of the laser is 2% using Rhodamine 6G dye.

Spectrally narrow pulsed dye laser without beam expander.

We have developed a simplified version of the side-pumped pulsed dye laser which has a spectral halfwidth of 1.25 GHz and a peak power of 10 kW at 600 nm. The basic laser consists of only four components (output mirror, dye cell, diffraction grating, and tuning mirror) and is exceptionally easy to align. Since the beam expander has been eliminated, the laser cavity can be made quite compact. Under the condition of reduced gain, the laser has been operated in a single mode.