From Photonics Rules of Thumb: Optics, Electro-Optics, Fiber Optics, and Lasers, Second Edition
LASER BEAM QUALITY
Beam quality is defined as
= (unitless) the wavefront error WFE expressed in waves
= Strehl ratio (unitless)
= RMS wavefront error in waves for errors less than about 1/5 of a wave
The best beam focusing and collimation that can be obtained is derived from the diffraction theory for plane and Gaussian beams encountering sharp-edged apertures, as described in virtually every optics and laser book. In those analyses, it is assumed that the wavefront is ideal and that there are no tilt or higher-order aberrations in the phase front. The concept of beam quality has been developed to deal simply with the additional impact of nonuniform phase fronts in those beams. In a wide variety of applications, this definition is used to characterize the spreading that will be encountered in focused or parallel beams, beyond that associated with diffraction.
There are many other definitions of beam quality, so the reader is cautioned to understand what is meant by "BQ" in a particular application.
These characterizations of a laser beam are effective measures when the beam is nearly diffraction limited. A typical guide is that Strehl ratio and beam quality can be related to the RMS wavefront error (regardless of the composition of the aberrations) if the errors are less than ?/5 (some references use ?/2 ? as the standard). For highly aberrated beams, it may be difficult to establish the beam quality. For example, using...
Products & Services
Topics of Interest
LASER BEAM SCINTILLATION Variance in the irradiance from a beam caused by turbulence can be estimated as follows for the special case of a horizontal beam path: where ? 2 t = 0.31 C n 2 k 7/6 L...
18.104.22.168 Second harmonic conversion of the phase-locked array The frequency doubler for the 100-J / pulse phase-locked laser system is a scaled version of that used for the 30-J / pulse...
Since the discovery of the laser in the 1960s, a great amount of research activity has led to an impressive increase of the overall performances of the sources emitting in the visible or in the...
22.214.171.124 Output beam quality In order to extract high-beam-quality output from the phase conjugated amplifier system, a high-quality input pulse must be provided. In ideal operation, the...
126.96.36.199 Operation with an SBS phase conjugator By replacing the Pockels cell in the regenerative amplifier ring with a 90o quartz rotator as depicted in Fig. 5.5, an injected pulse from...