Six-orders-of-magnitude-spanning dispersion measurement via Kalman filtering-aided white-light interferometry.

Dispersion plays a great role in ultrafast laser oscillators, ultrashort pulse amplifiers, and many other nonlinear optical dynamics. Therefore, dispersion measurement is crucial for device characterization, system design and nonlinear dynamics investigation therein. In this work, we demonstrate a versatile approach, i.e., Kalman filtering-aided white-light interferometry, for group delay dispersion (GDD) characterization. Extended Kalman filter is adopted to track the cosine-like interferogram, and to eliminate the unintended bias and the envelope, providing a nearly ideal phase retrieval and GDD estimation. The measurement range could span from tens of fs2 to tens of ps2, with an uncertainty of about 0.1%, enabling precise GDD measurement for diverse optical components, ranging from a millimeter-thick glass slide to highly dispersive chirped fiber Bragg gratings. Benefited by the simplicity, convenient setup, and easy operation as well as relatively low cost, this approach would help photonic device characterization, dispersion management and nonlinear dynamics investigation in the laboratory and work plant.

Stretch tuning of dispersion in optical microfibers.

Dispersion management is vital for nonlinear optics and ultrafast lasers. We demonstrate that group velocity dispersion (GVD, or second-order dispersion, i.e., ß2) and group delay dispersion (GDD) in optical microfibers can be tuned simply by stretch due to their remarkable features of small diameter and diameter-dependent dispersion. We experimentally demonstrate that a pulling force of just a few mN would elongate the optical microfibers by up to 5%, bringing a significant change in the ß2 and GDD. This change can be increment or decrement, lying on the diameter of optical microfibers. Therefore, 10-cm-long optical microfibers would provide a GDD change of 104 fs2 when elongated by 5%, well in the elastic limit. Remarkably, this change is equivalent to the GDD (not GDD change) provided by a 0.5-m-long single-mode fiber. Experimental results and simulations show that the GDD change is due to the interplay between elongation, diameter shrink, and refractive index decrease. Benefited from the easy manipulation, tiny pulling force required, and full integration with conventional optical fibers, stretch tuning of dispersion in optical microfibers would find applications in dispersion management for ultrafast lasers and nonlinear optics.

Risk factors for the occurrence of infection in patients with oral squamous cell carcinoma after restorative reconstruction and its impact on recurrence and quality of life: a retrospective cohort study.

Background: Worldwide, there are approximately 300,000 new cases of oral squamous cell carcinoma (OSCC) and 100,000 deaths each year. The complexity of oral and maxillofacial structures leads to a high risk of surgical infection such as radical tumor resection and free flap reconstruction. Previous studies have shown that diabetes mellitus, previous radiotherapy, oral-neck communication, etc. are risk factors for postoperative infection, but the influence of time on prognosis has not been clarified in detail. This study supplements this aspect and provided a reference for improving the quality of life of patients. Methods: We retrospectively analyzed a total of 168 patients who developed OSCC from July 2014 to September 2019. According to the inclusion and exclusion criteria of this study, the general data questionnaire designed by ourselves was used to sort out the general characteristics and clinical data of the subjects. The t test, Chi-square test and binary logistic regression were used for statistical analysis. Surgical site infections (SSI) are defined as infections associated with surgical procedures. The quality of life was evaluated by the 36-Item Short Form Survey (SF-36) score. A 3-year follow-up was conducted by telephone, Email and outpatient review. Results: Among the 168 patients, the total number of postoperative infections was 22 (13.1%). Binary logistic regression analysis showed that body mass index (BMI) (OR =0.029, P=0.039), American Society of Anesthesiologists (ASA) classification (OR =21.443, P=0.042), preoperative radiotherapy (OR =19.993, P=0.022), Jaw resection status (OR =29.665, P=0.021), Perioperative transfusion (OR =29.148, P=0.020), preoperative white blood cell count (OR =1.763, P=0.017), albumin level (OR =0.853, P=0.033) were independent influencing factors between the two groups (P<0.05). Except for the social functioning and role-emotional dimensions, all dimensions of SF-36 in patients with infection were significantly lower than those without infection. Conclusions: The incidence of postoperative infection after restorative and reconstructive surgery for OSCC deserves the attention of clinicians. For high-risk infected persons, relevant anti-infection measures should be taken early against the infectious source, and the possibility of nosocomial infection should be attached great importance in clinical work. After discharge, patients should also actively do follow-up, education and other related work to reduce the incidence of postoperative infection.

Kalman filtering-enhanced short-delay self-heterodyne interferometry for linewidth measurement.

We demonstrate an extended Kalman filtering-enhanced linewidth measurement in short-delay self-heterodyne interferometry (SDSHI). We found that a modified SDSHI trace closely resembles a biased cosine wave, which would enable convenient linewidth estimation by its uniform envelope contrast without any correction factor. Experimentally, we adopted this approach for kHz laser linewidth measurement, taking advantages of extended Kalman filtering (EKF) to adaptively track the cosine wave. Apart from the measurement noise suppression, this approach could use as many data points as possible in the noisy trace to make a linewidth estimation at each tracked data point, from which we can deduce valuable statistical parameters such as the mean and standard deviation. This approach involves no more equipment than conventional SDSHI and sophisticated EKF so that it can be easily implemented. Therefore, we believe it will find wide applications in ultra-narrow laser linewidth measurement.

[Evaluation of the fracture of nickel-titanium rotary Protaper during root canal preparation].

PURPOSE: To assess clinical application of Nickel-titanium(NiTi) rotary instruments Protaper in preparation of curved root canals. METHODS: 281 curved canals from 169 extracted molars were instrumented by Protaper rotary instruments using crown-down technique. An analysis was carried out regarding the relationship between the broken files and canal distribution,degree of curvature of canals, and the relationship between amount of the broken files and the duration was also included. SPSS18.0 software package was used for statistical analysis. RESULTS: A total of 43 kits files were used in the preparation of 281 curved root canals, and broken files often happened in canals with curvature of >30° and very complex canals. CONCLUSIONS: The fracture of NiTi instruments is closely related to the anatomy of the root cana1. With the use of NiTi rotary instruments Protaper, curved root canals can be prepared effectively. Meanwhile, the problem of instrument separation should be prevented.