An electro-optic effect is a change in the optical properties of a material in response to an electric field that varies slowly compared with the frequency of light. The term encompasses a number of distinct phenomena, which can be subdivided intoa) change of the absorption
Electro-absorption: general change of the absorption constants
Franz-Keldysh effect: change in the absorption shown in some bulk semiconductors
Quantum-confined Stark effect: change in the absorption in some semiconductor quantum wells
Electrochromic effect: creation of an absorption band at some wavelengths, which gives rise to a change in colour
Pockels effect (or linear electro-optic effect): change in the refractive index linearly proportional to the electric field. Only certain crystalline solids show the Pockels effect, as it requires lack of inversion symmetry
Kerr effect (or quadratic electro-optic effect, QEO effect): change in the refractive index proportional to the square of the electric field. All materials display the Kerr effect, with varying magnitudes, but it is generally much weaker than the Pockels effect
electro-gyration: change in the optical activity.
Electron-refractive effect or EIPM
Changes in absorption can have a strong effect on refractive index for wavelengths near the absorption edge, due to the Kramers–Kronig relation.Using a less strict definition of the electro-optic effect allowing also electric fields oscillating at optical frequencies, one could also include nonlinear absorption (absorption depends on the light intensity) to category a) and the optical Kerr effect (refractive index depends on the light intensity) to category b). Combined with the photoeffect and photoconductivity, the electro-optic effect gives rise to the photorefractive effect.
The term "electro-optic" is often erroneously used as a synonym for "optoelectronic".Main applications
3. Electro-optic field sensorsThe electro-optic Pockels effect in nonlinear crystals (e.g. KDP, BSO, K*DP) can be used for electric field sensing via polarisation state modulation techniques. In this scenario, an unknown electric field results in polarisation rotation of a laser beam propagating through the electro-optic crystal; through inclusion of polarisers to modulate the light intensity incident on a photodiode, a time-resolved electric field measurement can be reconstructed from the obtained voltage trace. As the signals obtained from vgccthe crystalline probes are optical, they are inherently resistant to electrical noise pickup, hence can be used for low-noise field measurement even in areas with high levels of electromagnetic noise in the vicinity of the probe. Furthermore, as the polarisation rotation due to the Pockels effect scales linearly with electric field, absolute field measurements are obtained, with no need for numerical integration to reconstruct electric fields, as is the case with conventional probes sensitive to the time-derivative of the electric field.
Electro-optic measurements of strong electromagnetic pulses from intense laser-matter interactions have been demonstrated in both the nanosecond and picosecond (sub-petawatt) laser pulse driver regimes. References
1. Castles, F. (2015-12-03). "Linear electro-optic effects due to high-order spatial dispersion". Physical Review A. American Physical Society (APS). 92 (6): 063804. arXiv:1503.04103. oi:10.1103/physreva.92.063804. ISSN 1050-2947.
2. Consoli, F.; De Angelis, R.; Duvillaret, L.; Andreoli, P. L.; Cipriani, M.; Cristofari, G.; Di Giorgio, G.; Ingenito, F.; Verona, C. (15 June 2016). "Time-resolved absolute measurements by electro-optic effect of giant electromagnetic pulses due to laser-plasma interaction in nanosecond regime". Scientific Reports. 6 (1): 27889. Bibcode:2016NatSR...627889C. doi:10.1038/srep27889. PMC 4908660. PMID 27301704.
3. Robinson, T. S.; Consoli, F.; Giltrap, S.; Eardley, S. J.; Hicks, G. S.; Ditter, E. J.; Ettlinger, O.; Stuart, N. H.; Notley, M.; De Angelis, R.; Najmudin, Z.; Smith, R. A. (20 April 2017). "Low-noise time-resolved optical sensing of electromagnetic pulses from petawatt laser-matter interactions". Scientific Reports. 7 (1): 983. Bibcode:2017NatSR...7..983R. doi:10.1038/s41598-017-01063-1. PMC 5430545. PMID 28428549.