Complete characterization of a Yb-based OPA at a high repetition rate using frequency resolved optical switching.

We demonstrate experimentally that frequency resolved optical switching (FROSt) can be used to characterize ultra-broadband pulses at high repetition rates up to 500 kHz. Specifically, we present the complete temporal characterization of an optical parametric amplifier (OPA), from the supercontinuum (SC) to the second stage of amplification. Simultaneous characterization of co-propagating signal and idler pulses enables retrieval of their group delay, as well as their temporal phase and intensity. Our study focuses on an extensive frequency range spanning the infrared region (1.2 to 2.4 µm) and confirms the strength and convenience of FROSt as a single tool for characterizing a wide range of pulses at high repetition rates.

Mid-infrared frequency domain optical parametric amplifier.

We report on an optical architecture delivering sub-120 femtosecond laser pulses of 20 µJ tunable from 5.5 µm to 13 µm in the mid-infrared range (mid-IR). The system is based on a dual-band frequency domain optical parametric amplifier (FOPA) optically pumped by a Ti:Sapphire laser and amplifying 2 synchronized femtosecond pulses each with a widely tunable wavelength around 1.6 and 1.9 µm respectively. These amplified pulses are then combined in a GaSe crystal to produce the mid-IR few-cycle pulses by means of difference frequency generation (DFG). The architecture provides a passively stabilized carrier-envelope phase (CEP) whose fluctuations has been characterized to 370 mrad RMS.

Comparison of psychometric properties of GOHAI, OHIP-14, and OHIP-EDENT as measures of oral health in complete edentulous patients aged 60 years and more.

OBJECTIVES: To compare the psychometric properties of three OHRQoL indicators (GOHAI, OHIP-14, and OHIP-EDENT) in a group of complete edentulous subjects and to explore the ability of these instruments to distinguish between individuals with different prosthetic and oral health status. METHODS: This was a cross-sectional study. Edentulous individuals aged 60 years and more were recruited between January 2019 and February 2020 in a medical and dental care centers. The Lebanese versions of GOHAI, OHIP-14, and OHIP-EDENT were used. External and internal consistencies were assessed using intraclass correlation coefficient (ICC) and Cronbach alpha, respectively. The concurrent validity was evaluated by testing the indicators against a proxy measure of a similar concept. To test their discriminative abilities, the ADD (GOHAI and OHIP) and SC (GOHAI and OHIP) scores were dichotomized according to the 25th and 75th percentile, respectively, and multivariate analyses were performed using sociodemographic, clinical, and subjective health parameters as explanatory variables. RESULTS: Two hundred and two edentulous subjects (age: 72.94 ± 7.378 years) were included. The proportion of subjects with no impact was lower for OHIP-EDENT (7.9%) compared to GOHAI (28.2%) and OHIP-14 (38.6%). Reproducibility was satisfactory for all OHRQoL tools since they were able to reproduce the results consistently in time (ICC > 0.80). The Cronbach alpha values were greater than 0.8 indicating acceptable internal consistency. The concurrent validity of the three tools was acceptable since subjects with lower OHRQoL score were less satisfied with their dentures and reported a higher need for self-rated therapy. Concerning the discriminant validity, OHIP-EDENT was more discriminant than OHIP-14 and GOHAI, since it was more able to identify patients with poor prosthetic issues or using instable denture. CONCLUSION: The OHIP-EDENT was more effective in identifying edentulous individuals with oral and prosthetic problems. Our results can help decide which dental instrument to use to assess the perception of oral health in edentulous individuals. More prospective studies are required to compare their evaluative properties.

10.4 kW coherently combined ultrafast fiber laser.

An ultrafast laser delivering 10.4 kW average output power based on a coherent combination of 12 step-index fiber amplifiers is presented. The system emits close-to-transform-limited 254 fs pulses at an 80 MHz repetition rate, and has a high beam quality (M2≤1.2) and a low relative intensity noise of 0.56% in the frequency range of 1 Hz to 1 MHz. Automated spatiotemporal alignment allows for hands-off operation.

Discrete dispersion scan setup for measuring few-cycle laser pulses in the mid-infrared.

In this work, we demonstrate a discrete dispersion scan scheme using a low number of flat windows to vary the dispersion of laser pulses in discrete steps. Monte Carlo simulations indicate that the pulse duration can be retrieved accurately with less than 10 dispersion steps, which we verify experimentally by measuring few-cycle pulses and material dispersion curves at 3 and 10 µm wavelength. This minimal measuring scheme using only five optical components without the need for linear positioners and interferometric alignment can be readily implemented in many wavelength ranges and situations.

Molecular gases for pulse compression in hollow core fibers.

We introduce hydrofluorocarbon molecules as an alternative medium to noble gases with low ionization potential like krypton or xenon to compress ultrashort pulses of relatively low energy in a conventional hollow core fiber with subsequent dispersion compensation. Spectral broadening of pulses from two different laser systems exceeded those achieved with argon and krypton. Initially 40 fs, 800 nm, 120 µJ pulses were compressed to few optical cycles duration. With the same approach a compression factor of more than 10 was demonstrated for an ytterbium-based laser (1030 nm, 170 fs, 200 µJ) leading to 15.6 fs.