Dermatologic Scar Assessment With Stereoscopic Imaging and Digital Three-Dimensional Models: A Validation Study.

BACKGROUND AND OBJECTIVE: We evaluated a new handheld stereoscopic imaging system capable of visualizing scars with digital three-dimensional (3D) models and providing automated morphometric estimates. The objective was to validate the repeatability and accuracy of intra- and inter-investigator scan results. STUDY DESIGN/MATERIALS AND METHODS: Engineered metal plates with depressed and elevated model scars (n = 72) were scanned six times by one investigator. In vivo hypertrophic and atrophic scars (n = 15) were scanned once by three investigators. The repeatability of morphometric estimates was assessed using coefficients of variation (CVs) to compare the variation among multiple scan results for both models and in vivo scars, with 0% reflecting a perfect match. Scar estimates from digital 3D reconstructions were compared with the known dimensions of physical model scars and with ruler measurements of in vivo scars. RESULTS: A total of 48 model scars and 12 in vivo scars were eligible for automated analyses with the imaging system's proprietary software. Intra-investigator scan results for the model scars were repeatable, with low variance for all parameters: volume, area, length, and depth/height (CV: 1.8-3.1%). By comparison, inter-investigator scans of real in vivo scars resulted in slightly higher median CVs (4.4-7.3%; P < 0.05). 3D model scar estimates correlated well with the known physical dimensions of model scars for all parameters (P < 0.001) and accurately reflected the measurements of in vivo scars (P < 0.001). The six in vivo scars situated on the chest and abdomen showed the highest inter-investigator variation, due to respiratory movement artifacts. CONCLUSION: Stereoscopic imaging of scars generates accurate and repeatable measurement estimates that show little intra- and inter-investigator-based assessment variation. The best results are achieved by minimizing subject movement. Lasers Surg. Med. © 2020 Wiley Periodicals LLC.

Phase locking and coherent combining of high-order-mode fiber lasers.

Efficient free-space configurations for phase locking and coherent addition of two fiber lasers, each operating with a high-order mode, are presented. Experimental results reveal that when the two fiber lasers are coupled, the polarization and modal distribution of one are imposed on the other. Coherent addition with a combining efficiency larger than 90% was achieved.

Simulataneous coherent and spectral addition of fiber lasers.

A new approach for the simultaneous coherent and spectral addition of a two-dimensional array of fiber lasers is presented. A combining efficiency of over 80% and a combined beam profile with M(2)=1.15 were experimentally obtained with an array of four fiber lasers. This approach can lead to significant upscaling in fiber laser additions.

Loss enhanced phase locking in coupled oscillators.

Phase locking, which is achieved by transferring some energy from one oscillator to the others, strongly depends on the coupling strength between the oscillators. Typically, the coupling strength must be above a certain threshold in order to achieve phase locking. Here we show how this threshold can be significantly reduced when phase-dependent losses are introduced into the oscillators. Specifically, the coupling strength can be reduced by at least an order of magnitude, thereby substantially decreasing the needed transfer of energy between oscillators. The resulting enhancement of phase locking does not only influence the laser research area, but also affects many other areas that involve coupled ensembles.

Efficient coherent addition of fiber lasers in free space.

An efficient technique in which fiber lasers are coherently added in free space is presented. Since the high power of the combined output light propagates in free space rather than inside, fiber optical damage and deleterious nonlinear effects are substantially reduced. Two different configurations are investigated. One involves conventional intracavity coupling between the lasers. The other is a novel configuration where the coupling is done out of the combined cavities. The latter configuration requires much less coupling for obtaining the same output power, so the damage to the fiber is further reduced.

Radio frequency photonic filter for highly resolved and ultrafast information extraction.

We present a method and devices for highly resolved carrier and information extraction of optically modulated radar signals. The extraction is done by passing the optical beam through a monitoring path that constitutes a finite impulse response filter. Replications of the monitoring signal realize the required spectral scan of the filter. Despite the fact that the filter configuration is fixed, each replication experiences different spectral filtering. The radar carrier is detected by observing the energy fluctuations in a low-rate output detector. The RF information is extracted by positioning a low-rate tunable filter at the detected carrier frequency.

Improving the output beam quality of multimode laser resonators.

Multimode laser operation is usually characterized by high output power, yet its beam quality is inferior to that of a laser with single TEM00 mode operation. Here we present an efficient approach for improving the beam quality of multimode laser resonators. The approach is based on splitting the intra-cavity multimode beam into an array of smaller beams, each with a high quality beam distribution, which are coherently added within the resonator. The coupling between the beams in the array and their coherent addition is achieved with planar interferometric beam combiners. Experimental verification, where the intra-cavity multimode beam in a pulsed Nd:YAG laser resonator is split into four Gaussian beams that are then coherently added, provides a total increase in brightness of one order of magnitude. Additional spectral measurements indicate that scaling to larger coherent arrays is possible.