How to Build a Laser Death Ray
The aspect ratio of a laser drilled hole is defined as the ratio of the hole's width to the hole's depth. A hole that is 0.5 cm wide at its entrance and tapers to a final depth of 10 cm has an aspect ratio of 20.
As a hole is being drilled, material which is ablated from the bottom of the hole by the laser can be re-deposited on the sides. Ejecta from the laser escaping through a deep, narrow hole can also interfere with the incoming laser beam. In addition, the hole itself blocks off the outer fringes of the laser, resulting in less light reaching the bottom of the hole, less energy absorption, and thus the next step of the hole is of narrower width, leading of a constricting taper as the hole gets deeper. All of these effects serve to limit the depth of the holes created by heat rays and blasters. Ray beams may be immune to these effects, since their plasma is transparent to theri high energy radiation, and the beam maintains a plasma channel for the remainder of the beam to shine through.
Practical experience with laser machining is that aspect ratios of 10:1 are easily acheivable, while the largest practical aspect ratios are about 20:1. Under highly controlled conditions, machined holes can obtain aspect ratios of 40:1 or even 100:1, but conditions in the field are not likely to allow such very deep holes for most death ray applications.
In laser machining, drilling in vacuum has been shown to allow larger aspect ratio holes than in air, because there is no air to impede and slow the escape of the ejecta. Space combat with death rays may allow somewhat deeper holes than combat in air.
In addition, higher power pulses and shorter duration pulses allow higher aspect ratio holes. Blasters are characterized by very short, high power pulses. It is thus reasonable to guess that blasters could routinely reach aspect ratios of 20:1, 30:1, or even more.
The recommendation for bullets intended for personal defense and police use is a penetration of 30 cm in human tissue, to allow reliable penetration of vital organs despite uncertain positioning of the target, intervening obstacles, and other uncertainties of combat. Anti-personnel death rays will need to meet similar requirements. This argues that laser sidearms and infantry weapons will make holes at least 1 cm to 1.5 cm wide in human targets.