Melles Griot Optics Guide - Real Beam Propagation

Gaussian Beam Optics

Real Beam Propagation

In the real world, truly Gaussian laser beams are very hard to find. Low-power beams from helium neon lasers can be a close approximation, but the higher the power of the laser, the more complex the excitation mechanism (e.g., transverse discharges,

Laser Modes

The Propagation Constant

Incorporating M² Into the Propagation Equations

flash-lamp pumping), and the higher the order of the mode, the more the beam deviates from the ideal.

To address the issue of non-gaussian beams, a beam quality factor, M ², has come into general use.

For a typical helium neon laser operating in TEM₀₀ mode, M ² <1.1. Ion lasers typically have an M ² factor ranging from 1.1 to 1.7. For high-energy multimode lasers, the M ² factor can be as high as 10 or more. In all cases, the M ² factor affects the characteristics of a laser beam and cannot be neglected in optical designs, and truncation, in general, increases the M ² factor of the beam.

In Laser Modes, we will illustrate the higher-order eigensolutions to the propagation equation, and in The Propagation Constant, M ² will be defined. The section Incorporating M ² into the Propagation Equations defines how non-Gaussian beams propagate in free space and through optical systems.

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