Prediction of pulse-to-pulse intensity fluctuation characteristics of high power ultrafast fiber amplifiers

Cataloged from PDF version of article.We report on the experimental characterization and theoretical prediction of pulse-to-pulse intensity fluctuations, namely, intensity noise, for ultrafast fiber amplifiers. We present a theoretical model with which the intensity noise of a Yb-doped fiber amplifier can be predicted with high accuracy, taking into account seed and pump noise, as well as generation of amplified spontaneous emission. Transfer of pump and seed signal modulations to the amplified output during fiber amplification are investigated thoroughly. Practically, our model enables design and optimization of fiber amplifiers with regards to their intensity noise performance. As a route to reducing noise imparted by pump diodes in a double-clad amplifier, we show the use of multiple, low-power diodes is more beneficial compared to a single, high-power diode due to the largely uncorrelated nature of their individual noise contributions. (C) 2014 AIP Publishing LLC

Home Is Where You Hang Your Hat: Host Town Identity, But Not Hometown Identity, Protects Against Mental Health Symptoms Associated with Financial Stress

Debt and financial insecurity are associated with stress, low self-worth, and poor health. Joining and identifying with social groups (social identification) promotes better health and higher self-esteem. Here, we examined whether identifying with one's local neighborhood protected people from developing mental health symptoms associated with financial stress. We analyzed data from a general population survey (Study 1, N = 4319) and a student mental health survey (Study 2, N = 612) conducted in the North West of England. We administered measures of financial stress, self-esteem, neighborhood identity, and mental health, and conducted moderated mediation analyses to test our predictions. Study 1 (population survey) demonstrated that stronger identification with one's local neighborhood attenuated the adverse effects of financial stress on self-esteem and subsequent mental health. Study 2 (student survey) showed that strong host town identities buffered students from mental health symptoms related to financial stress. Strong hometown identities, however, showed no buffering effect. The findings suggest that one way financial stress impacts mental health is by eroding self-esteem. Identifying with one's current place of residence appears to disrupt this pathway, while identifying with one's previous place of residence does not provide the same psychological protection. Read More: https://guilfordjournals.com/doi/10.1521/jscp.2018.37.3.15

Doping management for high-power fiber lasers: 100 W, few-picosecond pulse generation from an all-fiber-integrated amplifier

Cataloged from PDF version of article.Thermal effects, which limit the average power, can be minimized by using low-doped, longer gain fibers, whereas the presence of nonlinear effects requires use of high-doped, shorter fibers to maximize the peak power. We propose the use of varying doping levels along the gain fiber to circumvent these opposing requirements. By analogy to dispersion management and nonlinearity management, we refer to this scheme as doping management. As a practical first implementation, we report on the development of a fiber laser-amplifier system, the last stage of which has a hybrid gain fiber composed of high-doped and low-doped Yb fibers. The amplifier generates 100 W at 100 MHz with pulse energy of 1 mu J. The seed source is a passively mode-locked fiber oscillator operating in the all-normal-dispersion regime. The amplifier comprises three stages, which are all-fiber-integrated, delivering 13 ps pulses at full power. By optionally placing a grating compressor after the first stage amplifier, chirp of the seed pulses can be controlled, which allows an extra degree of freedom in the interplay between dispersion and self-phase modulation. This way, the laser delivers 4.5 ps pulses with similar to 200 kW peak power directly from fiber, without using external pulse compression. (C) 2012 Optical Society of Americ

Influence of modulation of pump and seed signals on fiber amplification of broadband pulses

We report on characterization of the transfer of pump and seed signal modulations, including noise, during fiber amplification. We demonstrate experimentally and theoretically that pump (signal) modulations are transferred only below (above) a cut-off frequency. © 2010 Optical Society of America

Ultrafast micromachining of Cu and Si at ultra-high repetition rates with pulse bursts

We report a novel ultrafast burst mode fiber laser system, which can deliver pulses at ultra-high repetition rates in order to systematically investigate micromachining efficiency on copper and silicon samples. © 2015 IEEE

Ablation-cooled material removal at high speed with femtosecond pulse bursts

We report exploitation of ablation cooling, a concept well-known in rocket design, to remove materials, including metals, silicon, hard and soft tissue. Exciting possibilities include ablation using sub-microjoule pulses with efficiencies of 100-mJ pulses. © OSA 2015

Global haplotype partitioning for maximal associated SNP pairs

<p>Abstract</p> <p>Background</p> <p>Global partitioning based on pairwise associations of SNPs has not previously been used to define haplotype blocks within genomes. Here, we define an association index based on LD between SNP pairs. We use the Fisher's exact test to assess the statistical significance of the LD estimator. By this test, each SNP pair is characterized as associated, independent, or not-statistically-significant. We set limits on the maximum acceptable proportion of independent pairs within all blocks and search for the partitioning with maximal proportion of associated SNP pairs. Essentially, this model is reduced to a constrained optimization problem, the solution of which is obtained by iterating a dynamic programming algorithm.</p> <p>Results</p> <p>In comparison with other methods, our algorithm reports blocks of larger average size. Nevertheless, the haplotype diversity within the blocks is captured by a small number of tagSNPs. Resampling HapMap haplotypes under a block-based model of recombination showed that our algorithm is robust in reproducing the same partitioning for recombinant samples. Our algorithm performed better than previously reported models in a case-control association study aimed at mapping a single locus trait, based on simulation results that were evaluated by a block-based statistical test. Compared to methods of haplotype block partitioning, we performed best on detection of recombination hotspots.</p> <p>Conclusion</p> <p>Our proposed method divides chromosomes into the regions within which allelic associations of SNP pairs are maximized. This approach presents a native design for dimension reduction in genome-wide association studies. Our results show that the pairwise allelic association of SNPs can describe various features of genomic variation, in particular recombination hotspots.</p