GOBI-IR — White Light Interferometer for GDD (IR, 900–2400 nm)

Our White Light Interferometer GOBI uses spectrally resolved interferometry to accurately measure the Group Delay Dispersion (GDD) of multi-layered ultrafast optics. The device has been developed at the Max-Planck-Institute of Quantum Optics (Garching, Germany) to characterize and refine some of the most advanced coatings to date.

Combining spectral with temporal information and the possibility to accumulate multiple passes over the same optic ensures reliable results. Spectrally resolved detection makes reference lasers — together with any related test-sample restrictions on specific reflection or transmission bands — obsolete. This opens the full spectral range to characterize even ultra-broadband or advanced narrowband coatings. The flexible optical setup can measure mirrors and transparent samples under angles of incidence variable between 0 and 70 degrees.

GOBI-IR (Infrared version) covers 900–2400 nm — the dedicated tool for characterizing infrared and mid-IR ultrafast coatings, including those for Cr:ZnSe, Ho:YAG, OPCPA pump-probe systems and other long-wavelength femtosecond sources. Spectral accuracy: 4 nm.

Key Product Features

• Direct spectrally dispersed measurement with a spectrometer
• No need for reference lasers, no requirements on specific reflectivity
• Ultrabroad spectral coverage — see Specifications tab for the three available versions
• s and p polarization measured separately
• Angle of incidence: 0° and 5–70°
• Measurement of single mirrors or mirror pairs
• Laptop and user-friendly software interface included
• Compact 45 × 45 cm² footprint

Working Principle

GOBI is based on a Michelson interferometer with an incoherent white light (WL) source. Data is acquired by scanning the delay of one arm and spectrally recording the evolving interference pattern. Fully automated analysis yields the spectral phase and GDD. The spectrometer directly provides the spectrally-resolved information, avoiding artefacts from time-domain reconstruction; it also provides an intrinsic calibration reference for the delay scan, so that no additional reference lasers are required. This makes GOBI suitable for any optics measurements in the detection range without the need to cover a reference laser wavelength in transmission or reflectance.

Sample Measurements

In contrast to other devices, GOBI is able to resolve strong GDD oscillations. Examples of GDD measurements compared with theoretical design include:

• Ultrabroadband PC70 mirrors — UFI's unique double-angle design, measured at 5° and 19° angle of normal incidence, together with the average.
• Pulse-compression mirror PC1921 — for the infrared.
• High-dispersive HD73 mirror — −3000 fs² per bounce at 1030 nm.

Note: differences between measured and theoretical curves reflect tolerances in the manufacturing process of the coatings.

References

1. M. Th. Hassan et al., "Optical attosecond pulses and tracking the nonlinear response of bound electrons," Nature 530, 66–70 (2016).
2. E. Fedulova et al., "Highly-dispersive mirrors reach new levels of dispersion," Optics Express 23 (11), 13788–13793 (2015).
3. V. Pervak, "Recent development and new ideas in the field of dispersive multilayer optics," Applied Optics 50 (9), C55–C61 (2011).