Group Delay Dispersion (GDD) in Optical Mirrors
Group delay dispersion (GDD) is an important optical phenomenon observed in the study of wave propagation, especially in ultrafast laser optics. It refers to the variation in the timing of different parts of an ultrafast laser pulse as it reflects off optical components such as mirrors. Understanding GDD is crucial for analyzing how these reflective surfaces stretch or compress the pulse.
Ultrafast pulsed lasers have a broader spectrum than single wavelength lasers, typically around 750–850 nm. To achieve an ultrashort pulse, wavelengths within this range need to be overlayed.
The material and coatings of optical components used in a laser system affect the shape of a laser pulse. Since the refractive index of an optical material changes with the wavelength (known as dispersion) and given the broadband nature of ultrafast laser pulses, in such systems there is a strong propensity for pulse distortion.
Ideally no change of the refractive index is desired. The GDD provides a gauge of the effect that an optical coating or element has on the pulse shape. If the GDD is zero, no distortion of the pulse takes place. Please see Manx Photonics’s technical paper for a more scientific explanation of this phenomenon.
In simple terms, scientists and laser system users would prefer no pulse distortion and a flat response GDD. This would allow for the best reflected or transmitted pulse, that is all wavelengths reflected or transmitted at the same GDD.
The full Manx article shows the effect of GDD on specific types of mirrors.
Understanding and precisely controlling GDD is critical for ensuring optimal performance in ultrafast laser systems, where both controlling pulse shape and timing are paramount. However, meeting the increasing demand for broader bandwidths, higher reflectivity, flatter GDD responses, and greater LDT poses significant design challenges. Balancing all four factors often requires trade-offs, and achieving perfect performance across the board can be an intricate, if not impossible, task.
About Manx Precision Optics
Manx Precision Optics (MPO) manufactures optical components and precision optics. The company offers customized products as well as a wide range of off-the-shelf components at highly competitive prices. The main categories of MPO’s standard products are: coated optics (including components for ultrafast lasers), uncoated optics, and polarization optics.
MPO works with customers to determine the most suitable optical coatings for their specific applications. With years of experience and an intimate knowledge of thin film coatings design, MPO can produce customized, quality coatings according to unique specifications.
To request more information or a quotation for Manx Precision Optics products, contact IL Photonics.