Imaging of THz Photonic Modes by Scattering Scanning Near-Field Optical Microscopy.

We investigated the near-field distribution associated to the photonic mode of terahertz photonic micro-resonators by scattering scanning near-field optical microscopy. Probing individual THz micro-resonators concentrating electric fields is important for high-sensitivity chemical and biochemical sensing and fundamental light-matter interactions studies at the nanoscale. We imaged both electric field concentration predicted by numerical simulations and unexpected patterns that deviate from intuitive assumptions. We propose a scenario based on the combination of the near-field with the far-field pattern of the probe/resonator ensemble that is in excellent agreement with the experimental data and propose an image analysis procedure to recover the near-field of such structures.

Short bends using curved mirrors in silicon waveguides for terahertz waves.

Dielectric waveguides are capable of confining and guiding terahertz waves along sub-wavelength sized structures. A small feature size allows for a denser integration of different photonic components such as modulators, beam-splitters, wavelength (de)multiplexers and more. The integration of components on a small scale requires bending of the waveguides. In this paper we demonstrate a very short silicon 90°-bend, based on total internal reflection on an elliptically curved outer facet and a rounding of the inner corner joining two waveguides, with an average loss of 0.14 dB per bend in the 600-750 GHz range.

Over-wavelength pitch sized diffraction gratings for augmented reality applications.

Waveguide based optical combiners for augmented reality (AR) glasses are integrating several surface relief gratings (SRG) whose pitch sizes can be as small as 200 nm for the blue wavelength. All SRG components exploit the first diffraction order to couple in and out or to deviate the light. We present SRG using higher diffraction orders featuring over-wavelength pitch sizes. Our gratings use the edge wave (EW) diffraction phenomenon to steer light in the preferred far field direction.

Proposal for an integrated silicon-photonics terahertz gas detector using photoacoustics.

A design and multiphysical model is presented for an on-chip gas sensor that transduces terahertz gas absorption through sound generation into a mechanical motion that can be read out externally. The signal is triply enhanced by designing a structure that functions simultaneously as an optical, an acoustical and a mechanical resonator. The structure is made in high-resistivity silicon and can be fabricated using CMOS and MEMS fabrication technologies. The sensor is a purely passive element, so an external THz source and read-out are required. The chip has a footprint of 3 mm2. A detection limit of 234 ppb of methanol for a source power of 1 mW and an integration time of 1 ms is predicted.

Optomechanical resonating probe for very high frequency sensing of atomic forces.

Atomic force spectroscopy and microscopy are invaluable tools to characterize nanostructures and biological systems. State-of-the-art experiments use resonant driving of mechanical probes, whose frequency reaches MHz in the fastest commercial instruments where cantilevers are driven at nanometer amplitude. Stiffer probes oscillating at tens of picometers provide a better access to short-range interactions, yielding images of molecular bonds, but they are little amenable to high-speed operation. Next-generation investigations demand combining very high frequency (>100 MHz) with deep sub-nanometer oscillation amplitude, in order to access faster (below microsecond) phenomena with molecular resolution. Here we introduce a resonating optomechanical atomic force probe operated fully optically at a frequency of 117 MHz, two decades above cantilevers, with a Brownian motion amplitude four orders below. Based on Silicon-On-Insulator technology, the very high frequency probe demonstrates single-pixel sensing of contact and non-contact interactions with sub-picometer amplitude, breaking open current limitations for faster and finer force spectroscopy.

Multi-MHz micro-electro-mechanical sensors for atomic force microscopy.

Silicon ring-shaped micro-electro-mechanical resonators have been fabricated and used as probes for dynamic atomic force microscopy (AFM) experiments. They offer resotnance frequency above 10MHz, which is notably greater than that of usual cantilevers and quartz-based AFM probes. On-chip electrical actuation and readout of the tip oscillation are obtained by means of built-in capacitive transducers. Displacement and force resolutions have been determined from noise analysis at 1.5fm/√Hz and 0.4 pN/√Hz, respectively. Despite the high effective stiffness of the probes, the tip-surface interaction force is kept below 1 nN by using vibration amplitude significantly below 100pm and setpoint close to the free vibration conditions. Imaging capabilities in amplitude- and frequency-modulation AFM modes have been demonstrated on block copolymer surfaces. Z-spectroscopy experiments revealed that the tip is vibrating in permanent contact with the viscoelastic material, with a pinned contact line. Results are compared to those obtained with commercial AFM cantilevers driven at large amplitudes (>10nm).

A novel dog-bone oscillating AFM probe with thermal actuation and piezoresistive detection.

In order to effectively increase the resonance frequency and the quality factor of atomic force microscope (AFM) probes, a novel oscillating probe based on a dog-bone shaped MEMS resonator was conceived, designed, fabricated and evaluated. The novel probe with 400 µm in length, 100 µm in width and 5 µm in thickness was enabled to feature MHz resonance frequencies with integrated thermal actuation and piezoresistive detection. Standard silicon micromachining was employed. Both electrical and optical measurements were carried out in air. The resonance frequency and the quality factor of the novel probe were measured to be 5.4 MHz and 4000 respectively, which are much higher than those (about several hundreds of kHz) of commonly used cantilever probes. The probe was mounted onto a commercial AFM set-up through a dedicated probe-holder and circuit board. Topographic images of patterned resist samples were obtained. It is expected that the resonance frequency and the measurement bandwidth of such probes will be further increased by a proper downscaling, thus leading to a significant increase in the scanning speed capability of AFM instruments.

Clinical practice guidelines for rest orthosis, knee sleeves, and unloading knee braces in knee osteoarthritis.

OBJECTIVE: To develop clinical practice guidelines concerning the use of bracing--rest orthosis, knee sleeves and unloading knee braces--for knee osteoarthritis. METHODS: The French Physical Medicine and Rehabilitation Society (SOFMER) methodology, associating a systematic literature review, collection of everyday clinical practice, and external review by multidisciplinary expert panel, was used. RESULTS: Few high-level studies of bracing for knee osteoarthritis were found. No evidence exists for the effectiveness of rest orthosis. Evidence for knee sleeves suggests that they decrease pain in knee osteoarthritis, and their use is associated with subjective improvement. These actions do not appear to depend on a local thermal effect. The effectiveness of knee sleeves for disability is not demonstrated for knee osteoarthritis. Short- and mid-term follow-up indicates that valgus knee bracing decreases pain and disability in medial knee osteoarthritis, appears to be more effective than knee sleeves, and improves quality of life, knee proprioception, quadriceps strength, and gait symmetry, and decreases compressive loads in the medial femoro-tibial compartment. However, results of response to valgus knee bracing remain inconsistent; discomfort and side effects can result. Thrombophlebitis of the lower limbs has been reported with the braces. Braces, whatever kind, are infrequently prescribed in clinical practice for osteoarthritis of the lower limbs. CONCLUSION: Modest evidence exists for the effectiveness of bracing--rest orthosis, knee sleeves and unloading knee braces--for knee osteoarthritis, with only low level recommendations for its use. Braces are prescribed infrequently in French clinical practice for osteoarthritis of the knee. Randomized clinical trials concerning bracing in knee osteoarthritis are still necessary.

Assessment of the test-retest reliability and construct validity of a modified WOMAC index in knee osteoarthritis.

OBJECTIVE: To assess the test-retest reliability and the construct validity of a modified version of the French-Canadian version of the WOMAC index. METHODS: Open prospective study conducted in departments of Rheumatology, Rehabilitation and Orthopedic surgery of a tertiary care teaching hospital. Eighty-eight patients with symptomatic knee osteoarthritis (OA) fulfilling the revised criteria of the American College of Rheumatology were included. The French-Canadian version of the WOMAC index was completed twice at a 3-h interval. Impairment outcome measures, patients' perceived discomfort in walking and handicap were recorded. An item-by-item analysis was performed. Test-retest reliability was assessed using the intra-class correlation coefficient (ICC) and the Bland and Altman method. Construct validity was investigated using the Spearman rank correlation coefficient and a factor analysis was performed. RESULTS: Eight questions assessing function (section C) and the two questions assessing stiffness (section B) had insufficient psychometric properties and were excluded. Although test-retest reliability of the questionnaire was fair to good (0.82, 0.85, for the WOMAC section A, and modified section C, respectively), construct validity could not be demonstrated. Factor analysis of the modified form of the WOMAC extracted four factors, which differed from the a priori stratification. However, factor analysis of the modified section C extracted two factors explaining 68.4% of the variance, which could be clinically characterized. CONCLUSION: Despite its good test-retest reliability, the modified WOMAC index is not valid for assessing pain and disability induced by knee OA in a French population. Section A and modified section C could be used separately to assess, respectively, pain and function.

Assessment of the test-retest reliability and construct validity of a modified Lequesne index in knee osteoarthritis.

OBJECTIVES: To assess the test-retest reliability and the construct validity of a modified version of the Lequesne index. METHODS: Patients with symptomatic knee osteoarthritis (OA) fulfilling the revised criteria of the American College of Rheumatology completed the Lequesne index twice at a 3-h interval. Impairment outcome measures and patients' perceived discomfort in walking and handicap were recorded. An item-by-item analysis was performed. Items having insufficient psychometric properties were excluded. Test-retest reliability was assessed using the intra-class correlation coefficient (ICC) and the Bland and Altman method. Construct validity was investigated using Spearman rank correlation coefficient and a factor analysis was performed. RESULTS: Eighty-eight patients were included. One question assessing pain (question IE) had a weak reliability (Kappa (kappa) = 0.39) and was excluded. The test-retest reliability of the modified questionnaire was excellent (ICC = 0.95). Expected convergent and divergent correlations were achieved except for visual analog scale pain (VAS P) and VAS handicap (VAS H) (0.46 and 0.40, respectively), and the "a priori" double stratification was confirmed by factor analysis, explaining 48.7% of the variance. CONCLUSION: The modified form of the Lequesne index has sufficient psychometric properties to be used to assess pain and function in knee OA in a French population.