Transverse and axial resolution of femtosecond laser ablation

Femtosecond lasers are capable of precise ablation that produce surgical dissections in vivo. The transverse and axial resolution of the laser damage inside the bulk are important parameters of ablation. The transverse resolution is routinely quantified, but the axial resolution is more difficult to measure and is less commonly performed. In some in vivo samples, fine dissections can also be difficult to visualize, but in vitro samples may allow clear imaging. Using a 1040-nm, 400-fs pulsed laser, we performed ablation inside agarose and glass, producing clear and persistent damage spots. Near the ablation threshold of both media, we found that the axial resolution is similar to the transverse resolution. We also ablated neuron cell bodies and fibers in C. elegans and demonstrate submicrometer resolution in both the transverse and axial directions, consistent with our results in agarose and glass. Using simple yet rigorous methods, we define the resolution of laser ablation in transparent media along all directions.

Transverse and Axial Resolution of Femtosecond Laser Surgery

Femtosecond lasers are capable of precise ablation inside transparent media, including glass and in vivo samples. The transverse and axial resolution of damage inside the bulk are important parameters of ablation. The transverse resolution is straightforward to measure, but the axial resolution is much more difficult to measure and rarely performed. Using a 1040-nm, 400-fs pulsed laser, we performed ablation inside glass with a transverse and axial resolution of 0.75 µm. By fitting damage spot measurements to theoretical predictions, we find an ablation threshold of 6.4 x 1012 W/cm2. We also ablated neuron cell bodies and fibers in C. elegans and demonstrate submicrometer resolution in both the transverse and axial directions, consistent with our results in glass. Using simple yet rigorous methods, we define the resolution of laser ablation in transparent media along all directions.

Pre-stack Time Migration Processing for Block A of Putaohua Oilfield

According to the reservoir and structural characteristics of Heidimiao, this paper combines fine pre-stack pre-processing and small-panel pre-stack time migration, and optimizes targeted methods and parameters to obtain the seismic data with higher resolution and better amplitude retention. Compared with the previous processing results, the migration imaging of the new data has been improved, and the geological phenomenon of the whole area is clear. The fracture system is reasonable, the fracture points are crisp, and the imaging of small faults is clear. The wave group characteristics of the new treatment are obvious, and the transverse resolution, longitudinal resolution and signal-to-noise ratio are improved obviously. By using relative amplitude preserving and VTI pre-stack time migration, the signal to noise ratio and resolution of seismic processing results have been greatly improved, and the interlayer information is more abundant, which can meet the needs of target interpretation.

Polyethylene-Carbon Composite (Velostat®) Based Tactile Sensor

The progress observed in ‘soft robotics’ brought some promising research in flexible tactile, pressure and force sensors, which can be based on polymeric composite materials. Therefore, in this paper, we intend to evaluate the characteristics of a force-sensitive material—polyethylene-carbon composite (Velostat®) by implementing this material into the design of the flexible tactile sensor. We have explored several possibilities to measure the electrical signal and assessed the mechanical and time-dependent properties of this tactile sensor. The response of the sensor was evaluated by performing tests in static, long-term load and cyclic modes. Experimental results of loading cycle measurements revealed the hysteresis and nonlinear properties of the sensor. The transverse resolution of the sensor was defined by measuring the response of the sensor at different distances from the loaded point. Obtained dependencies of the sensor’s sensitivity, hysteresis, response time, transversal resolution and deformation on applied compressive force promise a practical possibility to use the polyethylene-carbon composite as a sensitive material for sensors with a single electrode pair or its matrix. The results received from experimental research have defined the area of the possible implementation of the sensor based on a composite material—Velostat®.

Numerically focused optical coherence microscopy with structured illumination aperture

In optical coherence microscopy (OCM) with a given numerical aperture (NA) of the objectives the transverse resolution can be increased by increasing the numerical aperture of illumination (NAi). However, this may also lead to attenuation of the signal with defocus preventing the effective numerically focused 3D imaging of the required sample volume. This paper presents an approach to structuring the illumination aperture, which allows combining the advantages of increased transverse resolution (peculiar to high NAi) with small attenuation of the signal with defocus (peculiar to low NAi) for high-resolution numerically focused 3D imaging in OCM.

Detection of early osteoarthritis in canine knee joints 3 weeks post ACL transection by microscopic MRI and biomechanical measurement

Purpose: To detect early osteoarthritis (OA) in a canine Pond–Nuki model 3 weeks after anterior cruciate ligament (ACL) transection surgery, both topographically over the medial tibial surface and depth-dependently over the cartilage thickness. Methods: Four topographical locations on each OA and contralateral medial tibia were imaged individually by magnetic resonance imaging (MRI) at 17.6 µm transverse resolution. The quantitative MRI T2 relaxation data were correlated with the biomechanical stress-relaxation measurements from adjacent locations. Results: OA cartilage was thinner than the contralateral tissue and had a lower modulus compared to the contralateral cartilage for the exterior, interior, and central medial tibia locations. Depth-dependent and topographical variations were detected in OA cartilage by a number of parameters (compressive modulus, glycosaminoglycan concentration, bulk and zonal thicknesses, T2 at 0° and 55° specimen orientations in the magnet). T2 demonstrated significant differences at varying depths between OA and contralateral cartilage. Conclusion: ACL transection caused a number of changes in the tibial cartilage at 3 weeks after the surgery. The characteristics of these changes, which are topographic and depth-dependent, likely reflect the complex degradation in this canine model of OA at the early developmental stage.

Multimodal probe for optical coherence tomography epidetection and micron-scale indentation

We present a multimodal ferrule-top sensor designed to perform the integrated epidetection of Optical Coherence Tomography (OCT) depth-profiles and micron-scale indentation by all-optical detection. By scanning a sample under the probe, we can obtain structural cross-section images and identify a region-of-interest in a nonhomogeneous sample. Then, with the same probe and setup, we can immediately target that area with a series of spherical-indentation measurements, in which the applied load is known with a [Formula: see text]N precision, the indentation depth with sub-[Formula: see text]m precision and a maximum contact radius of 100[Formula: see text][Formula: see text]m. Thanks to the visualization of the internal structure of the sample, we can gain a better insight into the observed mechanical behavior. The ability to impart a small, confined load, and perform OCT [Formula: see text]-scans at the same time, could lead to an alternative, high transverse resolution, Optical Coherence Elastography (OCE) sensor.