Depolarization Compensator Compensates depolarization in the gain medium

We offer a new solution to solve the depolarization loss issue – a depolarization compensator.

It is a spatially variable wave plate (SVWP), fabricated knowing the level of depolarization, its origin, and amplified laser beam parameters.

This method is more beneficial than others, such as an intracavity quarter-wave plate, intracavity Faraday rotator, classical depolarization compensation layout with two identically pumped and relay-imaged gain media, and different crystal cut directions [1].

Due to the unique properties of precisely point-by-point inscribed nano-gratings, our depolarization compensator is flexible and versatile, and it can be widely adjusted according to customer needs.

ADVANTAGES VS. ALTERNATIVES

  • No absorption
  • Very low scattering
  • Custom and continuous point by point patterns
  • Maximum power extraction possibility without additional beam quality degradation
  • Flexibility to compensate different amounts of depolarization by stacking more than one element
  • Saves space, is easy to handle
  • Significantly lower price

WOP solution – depolarization compensator

Thermal effects in a high-power laser’s gain medium create predictable axially symmetric temperature gradients. Temperature gradients generate mechanical stresses in pumped crystal, which lead to induced birefringence.

Generated optical anisotropy causes significant power losses if a laser system contains polarization-sensitive elements (eg Brewster plates, Faraday rotators).

Workshop of Photonics | WOP, in a joint effort with Ekspla Ltd., based on Ekspla Ltd invention EP3712664 (A1), developed and verified a solution to solve the depolarization loss issue – an optical element that compensates distortion of original polarization in the gain medium.

A subpicosecond laser system was investigated, featuring fiber CPA-based seed laser FemtoLux 30 (Ekspla) and a double-pass end-pumped Yb:YAG crystal power amplifier [1].

The key novelty of the system was the application of depolarization compensation using a specially designed spatially variable wave plate or SVWP, which allowed the extraction of nearly maximum power from such an amplifier without additional beam quality degradation.

To the best of our knowledge, this method has been applied for the first time [1].

Depolarization compensator. Left: Two-dimensional distribution map of the orientation of fast and slow axes. Right: Retardance profile.

Our proposed depolarization compensation method – a depolarization compensator – is more beneficial compared to other methods, such as intracavity quarter-wave plate, intracavity Faraday rotator, classical depolarization compensation layout with two identically pumped and relay-imaged gain media, and different crystal cut directions.

The reasons are [1]:
  • the substrate of spatially variable wave plate (SVWP) is fused silica, providing low bulk absorption of laser radiation and featuring a significantly lower nonlinear refractive index, as compared to a Faraday rotator, thus minimizing thermal effects and nonlinear interaction in high-intensity lasers;
  • the SVWP element is compact (6 mm in thickness, usually 25.4 mm in diameter), whereas Faraday rotator material is usually at least 20 mm in length;
  • there is the possibility to compensate for depolarization in the highly pumped gain medium, which is not the case using a simple approach with a quarter-wave plate;
  • it is not overly sensitive to alignment and specific configuration;
  • it is very practical, as induced/compensated depolarization level can be tuned by either changing the incident laser beam size or stacking a few SVWPs in the same optical layout.

References

  1. Veselis, L., Burokas, R., Ulčinas, O., Gertus, T., Michailovas, K., & Michailovas, A. (2021). Depolarization compensation with a spatially variable wave plate in a 116 W, 441 fs, 1 MHz Yb: YAG double-pass laser amplifier. Applied Optics, 60(24), 7164-7171
  2. Michailovas Andrejus, Depolarization Compensator, EP3712664 (A1), 2019 03 20
  3. Aivaras Kazakevičius, Raimundas Burokas, Rokas Danilevičius, and Andrejus Michailovas, “Ultrafast 10 mJ, 100 W laser system featuring a directly laser written depolarization compensation element,” Opt. Express 32, 15326-15335 (2024)
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WORKSHOP OF PHOTONICS
Mokslininku st. 6A, Vilnius, LT-08412, Lithuania

Phone: +370 5 215 7551
E-mail: [email protected]

Company details

Altechna R&D, UAB
Company code 301502628
VAT code LT100006155012
Bank – SEB 70440
LT87 7044 0600 0770 8092