Source: PRIMES GmbH

Understanding Rayleigh Length in Laser Beams

What is Rayleigh Length?

The Rayleigh length (or Rayleigh range) of a laser beam is the distance from the beam waist where the beam radius is increased by a factor of the square root of 2. It is an important parameter for Gaussian beams and is determined by the beam waist radius and the wavelength of the laser beam.

Calculation of Rayleigh Length

The Rayleigh length can be calculated using the formula:

Rayleigh length = (π * Beam waist radius^2) / Wavelength

Effective Rayleigh Length

For beams with imperfect beam quality, the Rayleigh length is effectively decreased by the M2 factor, leading to larger beam divergence for a given beam waist radius.

Optimization of Beam Focusing

The Rayleigh length is crucial for determining the depth of focus when focusing a laser beam. It is recommended to focus the beam such that the Rayleigh length is of the order of the crystal length when interacting with optical elements like crystals for frequency doubling.

Stronger focusing can lead to higher optical intensities but over a shorter length due to increased beam divergence. Maintaining the (effective) Rayleigh length relative to the crystal length is essential for optimal performance.

Conclusion

Understanding the concept of Rayleigh length is vital for optimizing the performance of laser systems, particularly in applications involving beam focusing and interactions with optical elements.

Source: PRIMES GmbH
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