Ernest E. Bergmann

uv TEA laser with 760‐Torr N2

A simple reliable transversely excited atmospheric (TEA) laser operating with moderate repetition rates at 337 nm using commercial‐grade N2 at 1 atm is described. Preliminary results for a range of operating voltages and channel spacings are presented. The laser’s pulse width is about 1 nsec. Best electrical efficiency to date is 0.039% at 8.8 kV. At 21 kV, 355 μJ/pulse is obtained. Above 16.7 kV, the unfocused output will pump a dye solution to superradiance at a distance of 1.5 m. For supply voltages less than 10 kV, a novel configuration for preionization is described.

Compact TEA N2 laser

A novel pulsed uv laser that operates with pure N2 at 1 atm pressure is described. The length of the laser channel is only 25 cm, yet the laser is capable of producing over 0.5 MW peak power with less than 20 kV supplied to the circuit. Its simple construction should encourage widespread duplication.

Coherent uv from a TEA N2 laser system

A technique is described to couple and synchronize two transversely excited atmospheric (TEA) nitrogen lasers in an oscillator‐amplifier configuration to obtain spatially coherent 1‐nsec pulses at 337 nm with an energy/pulse of several hundred microjoules. The technique should be adaptable to other very high gain laser systems whose operation terminates so quickly as to render optical resonators impractical.

Optical resonators with paraxial modes.

The theory of a large class of optical resonators has been developed in a compact form by the means of raising and lowering differential operators (commonly used in quantum mechanics). The theory is applicable to any cavity for which paraxial ray theory may be applied successfully and where losses, aperturing, and aberrations can be ignored. The resonator need not be planar (so that image rotation may occur), the optical elements may be astigmatic and the optic axis incompletely defined (such as when dispersive prisms are used). A discussion of existence and uniqueness of paraxial (pencillike) modes is provided, including the modification of the theory when degeneracies are present. It is proved that unstable cavities do not possess paraxial modes.

Measurement of nanosecond HV transients with the Kerr effect

A technique for measuring the high‐voltage transients associated with low inductance, pulsed gas discharges is described. Measurements are made directly at the 10‐kV level with a transmission line Kerr cell and narrow‐width, pulsed dye laser, synchronized with the test discharge. The data indicates a temporal resolution of 2 ns.

Schlieren and interferometric study of a laser triggered air spark in the nanosecond regime

The growth of the plasma column and the electron density in an atmospheric air spark are studied by photographs. A 1‐ns nitrogen laser provides the light source and the trigger. The relative timing is controlled by an adjustable light path length. It was found that the spark bridges the 0.5‐mm gap during the first 5 ns. The plasma column diameter then grew linearly with time for 25 ns at a speed of 10.5 km s−1. The electron density in the ionized channel is found from interferograms; it reached a maximum value of 6.5×1019 cm−3 at 8 ns.

Nanosecond evolution of a low‐inductance air spark

The expansion of the shock front of a laser‐triggered, atmospheric air spark was studied by shadow photography with a transversely excited atmospheric UV nitrogen laser. It was found that the shock front of the short spark (0.5 mm) was cylindrical. Within a few nanoseconds of spark formation the diameter of the spark channel grows linearly with time and the index of refraction is less than in the surrounding gas. The shock velocity was measured to be 7 km/s (Mach 20).

Simple Kinematic Laser Mirror Mount

A simple kinematic laser mirror mount is described which permits one to orient an optical component about vertical and horizontal axes which, to lowest order, pass through the center of the component. The use of magnets permits rapid interchange of optics without loss of orientation.

Collision‐induced transitions in neon

The interaction of 6328‐A laser radiation with excited atoms in a He‐Ne gas discharge leads to a sizeable change in the population of the 3s2 and 2p4 levels of Ne. Population of levels connected to the upper and lower laser levels through radiative and nonradiative electronic and/or atomic collisional processes will be perturbed also by the population changes of these two levels. By studying the intensity changes of spontaneous emission from the 3s2 and 3s3 levels as a function of current and pressure, we obtained the total relative atomic and electronic deexcitation rates of the 3s3 level. We also studied the collisional coupling between the 3s2 and 4d4 levels of Ne (the ion cores of which are in two different states) to find the total atomic and electronic deexcitation rates for the 4d4 level. The electronic coupling between these two levels was found to be weaker than between the 3s2 and 3s3 levels, suggestive of a weak selection rule.

Simple Phase Adjustment for ``Difference'' Holography

A simple, readily implemented method of changing the optical phase of the reference beam is described. A thin glass microscope coverslip is obliquely introduced into the beam. Slight tilting, which can be effected in complete darkness, produces the controlled phase change.