Group Velocity Delay Compensators operate based on the principle of dispersion compensation, which aims to counteract the broadening of optical pulses that occurs as the pulses propagate through dispersive optical elements. Temporal dispersion leads to pulse stretching, wherein different spectral components of the pulse propagate at different velocities (the phenomenon is called Group Velocity Mismatch/GVM), causing the pulse to elongate in time. Group Velocity Delay Compensators enable precise manipulation of the group velocity of light pulses in the domain of femtosecond lasers, compensating for temporal dispersion effects and ensuring the generation of ultrashort pulses with minimal distortion.

North Optics offers off-the-shelf and custom Group Velocity Delay (GVD) Compensation Plates for femtosecond lasers. The group velocity delay compensators are optimized for offsetting the specified amount of time delay between the fundamental wavelength and the harmonic wavelength of orthogonal polarizations. As explained above, attributing to the group velocity mismatch between different wavelengths, a temporal dispersion exists between the fundamental and harmonic wavelengths. A time delay compensation plate introduces controlled amounts of dispersion opposite in sign to that of the dispersive elements, neutralizing the temporal dispersion and restoring the pulse duration to its original, shorter duration. 

The precise delay time can be controlled by rotating the compensator - changing the angle of incidence (AOI) of the laser beams to the plate. The recommended range of the AOI for North Optics’s Group Velocity Delay Compensators is +/-12°. We offer group velocity compensators made of two materials: Calcite group velocity delay compensators and Alpha-BBO group velocity delay compensators. The standard calcite and BBO crystal plates are rectangular with a 12mm clear aperture and mounted with a ring. Standard operating wavelengths include 800nm/400nm, 1030nm/515nm, and 600nm/300nm, while other custom-specified wavelengths and delay amounts can be tailored upon request. 

Application Notes:

1. The suggested angular tuning range for North Optics’s group velocity delay compensator is AOI +/-12°. However, if beam clipping at the edge of the compensator is not a concern, a more significant rotation can be applied to obtain an expanded delay range.

2. In calcite plates, the optical axis is positioned at a specific orientation that is not parallel to the faces of the plate. Therefore, it's crucial to account for the walk-off effect observed for e-polarized beams, as well as the displacement of both beams when operating at non-zero angles of incidence (AOI) in real-world application scenarios.

Common Specifications:

Basic Properties of Calcite:

Basic Properties of Alpha-BBO Crystal: