Optical Link as an Alternative for MRI Receive Coils: Toward a Passive Approach.

Objective: The objective of this work was to propose an alternative solution to NMR signal transmission by replacing the coaxial cables of the receiver radiofrequency (RF) coil in the context of MRI so as to improve safety. Starting from the analysis of previous studies and reports on the topic, the difficulty of supplying power wirelessly to an RF coil was identified. To avoid this difficult task, the development of a passive analog optical link was studied.

Sub-wavelength terahertz imaging through optical rectification.

We record a sub-wavelength terahertz image of a caster sugar grain thanks to optical rectification in the sample excited with a femtosecond laser beam. The lateral spatial resolution of this technique is given by the laser spot size at the sample and here its measured value is 50 μm, i.e.

Full electro-optic terahertz time-domain spectrometer for polarimetric studies.

We present a terahertz (THz) time-domain spectrometer dedicated to polarimetric studies. THz pulses are generated through optical rectification in a ⟨111⟩-cut cubic crystal. The ⟨111⟩ crystal cut produces a THz polarization state similar to that of the exciting laser beam.

Electro-optic probe for real-time assessments of RF electric field produced in an MRI scanner: Feasibility tests at 3 and 4.7 T.

During magnetic resonance imaging (MRI) examinations, the average specific absorption rate (SAR) of the whole body is calculated as an index of global energy deposition in biological tissue without taking into account the presence of metallic implants or conductive materials. However, this global SAR calculation is not sufficient to ensure patient safety and a local SAR measurement should be carried out. Several measurement techniques have already been used to evaluate the local SAR, in particular electric field (E-field) probes, but the accuracy of the measurements and the resolutions (spatial and temporal) depend strongly on the measurement method/probe.

Electric field and temperature measurement using ultra wide bandwidth pigtailed electro-optic probes.

We present pigtailed electro-optic probes that allow a simultaneous measurement of high frequency electric fields and temperature using a unique laser probe beam. This has been achieved by the development of a novel probe design associated with a fully automated servo-controlled optical bench, initially developed to stabilize the electric field sensor response. The developed electro-optic probes present a stable response in outdoors conditions over a time duration exceeding 1 h, a frequency bandwidth from kHz to tens of GHz with a sensitivity of 0.

High-finesse Fabry-Perot electro-optic sensors with enhanced sensitivity and high spatial resolution.

We present a high-finesse optical cavity containing a LiTaO(3) electro-optic crystal, devoted to free-space electric field characterization. Theoretical considerations will show that the modulation depth is directly related to the transversal components of the field to be measured, thus opening the way to vectorial mapping of the electric field using a single electro-optic crystal. Also, a discussion about noise and sensitivity will be given.