Optical lasers all operate according to the same fundamental principles despite the fact that there is considerable variation in the details, particularly in regard to scaling. Small, hand-held laser pointers may be energized by single AAA dry cells while the largest lasers are huge machines powered by nuclear reactors.
All lasers consist of resonant cavities. Light bounces off reflective surfaces at either end, confined to a single frequency by the resonant property of the enclosure. The laser beam emerges at one end through a partially reflective port. A key part of the picture is an energy source sitting nearby. It injects light or electrical power into the enclosure on a continuous basis. This device is known as the laser pump, and without it there can be no laser action.
The light that emerges is confined to a single frequency and is polarized, meaning the waveforms oscillate along a single plane. Not only is the frequency uniform (a simple filter would do that), but the waveforms are accurately synchronized. For this reason, the light rays do not interfere with one another. Consequently, the beam does not spread in a widening cone, unlike the light from a conventional parabolic reflector. Accordingly, when a laser beam is aimed at a distant target, the full power transfers to a tiny area.
The most powerful lasers available today are rated at 500 trillion watts. That is 1,000 times more power than that used in the U.S. at any given instant. This is possible only because the laser beam is emitted in pulses of short duration, so the comparison can be misleading. Nevertheless, the intensity of the beam is awesome – an earth-based laser is capable of blasting rock on the surface of the moon.
Many lasers, including short pulse machines, have been specifically designed for military purposes. A high-powered narrow beam can cause immense destruction in real time at a remote location.
An extremely high-powered laser built for non-military purposes sits at the Berkeley Lab Accelerator (BELLA). It fired a 40 femtosecond pulse on July 20, 2012, at that instant becoming the world’s most powerful laser. Each pulse had a compressed output energy of 42.2 joule, for a total power output of the laser of 1 petawatt.
The Berkeley laser was developed to operate in conjunction with particle accelerators, which require a highly localized (spatially and temporally) pulse of energy. This is accomplished by the production of electron density waves, moving through plasma. The ensuing laser beam travels through gas or plasma enclosed in sapphire or other crystalline material. Free electrons are accelerated to high energy levels in short pulses. That accounts for their intensity.
Filed Under: Test & Measurement Tips