Waveplates

Waveplates are vital devices actively used to manipulate the polarization of light. They achieve this manipulation by introducing retardation in birefringent crystals. When the electric field aligns at a 45-degree angle to the optical axis of the waveplate, it induces a phase delay, causing extraordinary polarization to experience a delay compared to ordinary polarization.  

The thickness of the waveplate determines the amount of retardation, allowing specific values like 180 degrees or 90 degrees. A λ/2 waveplate with 180-degree retardation alters the polarization direction by 90 degrees, while a λ/4 waveplate with 90-degree phase retardation generates circular polarization. Careful selection of the waveplate’s thickness enables achieving custom retardation values for specialized applications.  

Designing waveplates in various configurations is possible. The zero-order configuration, where two crystalline quartz plates optically contact with crossed optical axes, and the zero-order air-spaced configuration, employing crystalline quartz plates mounted with a spacer between them, are common options. Both configurations actively provide designed retardation across a broad wavelength bandwidth, typically exceeding 20 nm.

Certain applications, like long-pulse laser operations with power levels below tens of watts, actively utilize the multi-order configuration. This involves a single crystalline quartz waveplate with a typical thickness of approximately 1 mm.

To minimize surface reflections, crystalline quartz waveplates are actively coated with antireflection coatings, which reduce reflections to less than 0.2%. Achieving even higher transmission levels is possible with ion beam sputtering (IBS) coatings, which bring reflection values down to less than 0.1%.

The waveplates’ robustness is evident in their laser-induced damage threshold (LIDT) measurements, showing values exceeding 10 J/cm² when tested with a 1064 nm wavelength, 10 ns pulse duration, and 100 Hz repetition rate (according to the 10³-on-1 test, ISO 21254-2). This high LIDT actively ensures the waveplates’ reliability and suitability for demanding laser applications.