Decoherence due to XPM-assisted Raman amplification for polarization or wavelength offset pulses in all-normal dispersion supercontinuum generation

We report the importance of cross-phase modulation (XPM) on the coherence of a low-energy probe pulse co-propagating with a high-energy pump pulse that generates incoherent supercontinuum in all-normal dispersion (ANDi) fiber due to Raman amplification of quantum noise. By investigating numerous fiber and pulse parameters, we show consistently that for weak probe pulses, the XPM from the pump is the dominant influence on the degradation of the probe coherence. We show that the faster decoherence at the pump leading edge means that the probe coherence is reduced more significantly when the probe has a higher group velocity, i.e., when an orthogonally polarized probe is aligned to the fast (lower refractive index) axis of the fiber or when a co-polarized probe has a longer central wavelength. Simulations show that this effect occurs for both polarization-maintaining (PM) and non-PM ANDi fibers and can result in a probe decoherence rate that is higher than that of the pump. These previously unreported results extend our earlier scalar simulations showing incoherent supercontinuum within a single pulse

Noise-related polarization dynamics for femto and picosecond pulses in normal dispersion fibers

We report how the complex intra-pulse polarization dynamics of coherent optical wavebreaking and incoherent Raman amplification processes in all-normal dispersion (ANDi) fibers vary for femto and picosecond pump pulses. Using high temporal resolution vector supercontinuum simulations, we identify deterministic polarization dynamics caused by wavebreaking and self-phase modulation for femtosecond pulses and quasi-chaotic polarization evolution driven by Raman amplification of quantum noise for picosecond pulses. In contrast to cross-phase modulation instability, the Raman-based polarization noise has no power threshold and is reduced by aligning the higher energy polarization component with the lower index axis of the fiber. The degree of polarization stability is quantified using new time domain parameters that build on the spectrally averaged degree of coherence used in supercontinuum research to quantify the output spectral stability. We show that the spectral coherence is intrinsically linked to polarization noise, and that the noise will occur in both polarization maintaining (PM) and non-PM fibers, spanning a broad range of pulse energies, durations, and fiber birefringence values. This analysis provides an in-depth understanding of the nonlinear polarization dynamics associated with coherent and incoherent propagation in ANDi fibers

Higher adherence to a Mediterranean diet Is associated with improved insulin sensitivity and selected markers of inflammation in individuals who are overweight and obese without diabetes

Insulin resistance (IR) and chronic low-grade inflammation are risk factors for chronic diseases including type 2 diabetes (T2D) and cardiovascular disease. This study aimed to investigate two dietary indices: Mediterranean Diet Score (MDS) and Dietary Inflammatory Index (DII®), and their associations with direct measures of glucose metabolism and adiposity, and biochemical measures including lipids, cytokines and adipokines in overweight/obese adults. This cross-sectional study included 65 participants (males = 63%; age 31.3 ± 8.5 years). Dietary intake via 3-day food diaries was used to measure adherence to MDS (0–45 points); higher scores indicating adherence. Energy-adjusted DII (E-DII) scores were calculated with higher scores indicating a pro-inflammatory diet. IR was assessed using hyperinsulinemic euglycemic clamps, insulin secretion by intravenous glucose tolerance test, adiposity by dual-energy X-ray absorptiometry, and circulating cytokine and adipokine concentrations by multiplex assays. Higher MDS was associated with greater insulin sensitivity (β = 0.179; 95%CI: 0.39, 0.318) after adjusting for age, sex and % body fat, and lower NF-κB, higher adiponectin and adipsin in unadjusted and adjusted models. Higher E-DII score was associated with increased total cholesterol (β = 0.364; 95%CI: 0.066, 0.390) and LDL-cholesterol (β = 0.305; 95%CI: 0.019, 0.287) but not with adiposity, glucose metabolism, cytokines or adipokines. Greater MDS appears to be associated with decreased IR and inflammatory markers in overweight/obese adults

Supercontinuum generation with femtosecond pulse fiber amplified VECSELs

We present a mode-locked VECSEL emitting 400-fs pulses at a 3 GHz repetition rate at 1040 nm, amplified by a cascaded ytterbium doped fiber amplifier system to an average power of 40 W. The 3-ps duration amplified pulses are recompressed to their original 400-fs duration using a high-throughput transmission grating compressor. The recompressed pulses are used to generate supercontinuum with two different photonic crystal fibers (PCFs); an all-normal dispersion PCF and a PCF with a zero-dispersion wavelength at 1040 nm, creating spectra with 20 dB bandwidths of 200 nm with 3.9 W average power and 280 nm with 2.5 W average power respectively

Simulations and experiments showing the origin of multi-wavelength mode locking in femtosecond, Yb-fiber lasers

A stable and self-starting femtosecond breathing-pulse Yb-fiber oscillator is reported, modelocked using the nonlinear polarisation evolution mechanism. A bifurcation between two distinct modes of operation is demonstrated experimentally, producing pulses with a single central wavelength in one state, or following adjustment of the intra-cavity waveplates, the emission of pulses with three distinct central wavelengths. The maximum bandwidth was 72 nm at the -10 dB level and the pulses were compressible externally to 70 fs with energies of 0.75 nJ. The multi-wavelength pulses reported here are significantly shorter than the pico-second pulses previously observed from similar modelocked multi-wavelength sources. Vector simulations based on the nonlinear Schrödinger equation show that the multi-wavelength behaviour is produced by overdriving the nonlinear polarisation evolution based saturable absorber at the peak of the pulse, leading to transmission of the two wings of the strongly chirped pulse. This new insight shows clearly that the three pulses output in the multi-wavelength state are coherent. The agreement between simulation and experimental data shows nonlinear polarisation evolution based modelocked fiber lasers are a suitable platform for studying the nonlinear dynamics underlying the bifurcation of the output

Computer-automated design of mode-locked fiber lasers

We automate the mode-locked fiber laser design process using a modified genetic algorithm and an intuitive optimization loss function to control highly accurate polarization resolved simulations of laser start-up dynamics without user interaction. We reconstruct both the cavity designs and output pulse characteristics of experimentally demonstrated Yb-fiber all-normal dispersion, dispersion-managed, and wavelength-tuneable all-anomalous dispersion Tm-fiber femtosecond lasers with exceptional accuracy using minimal prior knowledge, and show that our method can be used to predict new cavity designs and novel mode locking states that meet target pulse requirements. Our approach is directly applicable to a broad range of mode locking regimes, wavelengths, pulse energies, and repetition rates, requires no training or knowledge of the loss function gradients, and is scalable for use on supercomputers and inexpensive desktop computers

Efficient high-harmonic generation from a stable and compact ultrafast Yb-fiber laser producing 100 micro-joule, 350 fs pulses based on bendable photonic-crystal fiber

The development of an Yb3+-fiber based chirped-pulse amplification system and the performance in the generation of extreme ultraviolet (EUV) radiation by high-harmonic generation is reported. The fiber laser produced 100 µJ, 350 fs output pulses with diffraction limited beam quality at a repetition rate of 16.7 kHz. The system used commercial single-mode, polarization maintaining fiber technology. This included a 40 µm core, easily packaged, bendable final amplifier fiber in order to enable a compact system, to reduce cost, and provide reliable and environmentally stable long term performance. The system enabled the generation of 0.4 µW of EUV at wavelengths between 27-80 nm with a peak at ~45 nm using xenon gas. The EUV flux of ~1011 photons per second for a driving field power of 1.67 W represents state-of-the-art generation efficiency for single-fiber amplifier CPA systems, corresponding to a maximum calculated energy conversion efficiency of 2.4 x 10-7 from the infra-red to the EUV. The potential for high average power operation at increased repetition rates and further suggested technical improvements are discussed. Future applications could include coherent diffractive imaging in the EUV, and high-harmonic spectroscopy

Yb-fiber amplifier pumped idler-resonant PPLN optical parametric oscillator producing 90 femtosecond pulses with high beam quality

An idler-resonant femtosecond optical parametric oscillator (OPO) with near-diffraction-limited beam quality (M2 ~ 1.05) at ~2.4 µm is demonstrated. The OPO is synchronously pumped by a femtosecond Yb-fiber amplifier system providing 130 fs pulses with an average power of 4.5 W at 1,050 nm and delivers 90 fs pulses with maximum average powers of 600 mW for the idler and 670 mW for the signal. Tunability is demonstrated across idler (signal) wavelengths from 2.2 to 2.6 µm (1.76 - 2.0 µm), limited only by the OPO mirrors. As a demonstration of the utility of the source, the idler pulses are used to generate a supercontinuum from 1,600 to 3,200 nm in a silicon-core fiber

GO/Fe3O4/SO3H Nano-Catalysts for Waste Cellulose Conversion

We report supercontinuum generation using a mode-locked VECSEL emitting 400-fs pulses at a 3-GHz repetition rate, amplified with a cascaded ytterbium-doped fiber amplifier system up to 40 W of average power. The pulses were then recompressed to their original duration via a high throughput transmission grating compressor, and used to generate supercontinuum in two samples of photonic crystal fiber (PCF); an all-normal dispersion PCF, and a PCF with a zero dispersion wavelength of 1040 nm, creating spectral bandwidths of 200 nm and 515 nm respectively