Decomposition in soil and chemical changes of maize roots with genetic variations affecting cell wall quality

Summary Roots of brown-midrib (F2bm1 and F292bm3) maize mutants and their normal isogenic counterparts (F2 and F292) were used to evaluate the changes in chemical cell wall features with regard to polysaccharides, lignin composition and interconnecting phenolic acids during root degradation in soil. To this end, the chemical variability of roots of brown-midrib mutants and their normal counterparts was compared and its subsequent impact on carbon (C) mineralization determined under controlled conditions. The bm1 mutation mainly caused an increase in lignin content and a decrease in polysaccharide content of maize roots whereas the bm3 mutation caused only a decrease in polysaccharide content. The lignin composition of bm roots differed from that of normal lines and the proportion of cell wall ester-linked hydroxycinnamic acids was also different. C mineralization kinetics differed markedly between the genotypes. Certain relevant factors concerning root decomposition in soil were studied from the relationships between the chemical characteristics of maize roots at different stages of decomposition and C mineralization rates. The Klason lignin-to-glucose ratio (KL/Glu), the Klason lignin-to-arabinoxylans ratio (KL/AX) and the arabinose-to-xylose ratio (A/X) were proposed as promising predictive indicators of C mineralization kinetics. Future estimations of soil residue decomposition could be improved by taking these initial chemical criteria into account on a wider range of residues. Décomposition dans le sol et évolution de la qualité chimique des racines de maïs présentant des modifications génétiques de la qualité des parois cellulaires' Résumé Les racines des maı¨s mutants brown-midrib (F2bm1 et F292bm3) et celles de leurs ligne´es isoge´niques normales (F2 et F292) ont e´te´utilise´es pour e´valuer les modifications des caracte´ristiques chimiques des parois cellulaires, a`travers la composition des polysaccharides, de la lignine et la nature des acides phe´noliques, au cours de la de´gradation des racines dans le sol. Pour cela, nous avons examine´, en conditions controˆle´es, l'impact d'une variabilite´de la qualite´chimique des racines, en comparant les mutants bm et leurs ligne´es isoge´niques normales, sur la mine´ralisation du C. La mutation bm1 engendre principalement une augmentation de la teneur en lignine et une diminution de la teneur en polysaccharides dans les racines de maı¨s alors que la mutation bm3 cause uniquement une diminution de la teneur en polysaccharides. Dans les racines des mutants bm, la composition de la lignine ainsi que les proportions en acides hydroxycinnamiques este´rifie´s des parois cellulaires diffe`rent de celles des ligne´es non mutantes. Les cine´tiques de mine´ralisation du C varient fortement entre les ge´notypes. Les relations entre les caracte´r-istiques chimiques des racines de maı¨s a`diffe´rents stades de de´composition et les taux de mine´ralisation du C ont permis d'e´tudier certains facteurs pertinents concernant la de´composition des racines dans le sol. Les rapports lignine Klason sur glucose (KL/Glu), lignine Klason sur arabinoxylanes (KL/AX) et arabinose sur xylose (A/X) ont e´te´identifie´s comme e´tant de bons indicateurs de pre´diction des cine´tiques de mine´ralisation du C. La prise en compte de ces crite`res de qualite´chimique initiale sur une plus large gamme de re´sidus pourrait ame´liorer l'estimation de la de´composition des re´sidus dans le sol

Properties of a microjoule-class fiber oscillator mode-locked with a SESAM

Energy scaling of ultrafast Yb-doped fiber oscillators has experienced rapid progress largely driven by many applications that require high average power femtosecond pulses. The fundamental challenge for ultrafast fiber lasers relies on the control of excessive nonlinearity, which limits pulse energy. The development of all-normal dispersion laser cavities based on large-mode-area photonic crystal fibers (PCFs) has enabled significant energy scaling [1-3]. In particular, up to microjoule energy levels have been achieved from rod-type fiber-based oscillators [2-3]. In such lasers, pulse shaping is dominated by the strength of the mode-locking mechanism which determines the pulse properties. In this contribution, we report the generation of high-energy sub-picosecond pulses from a highly normal dispersion fiber laser featuring an Yb-doped rod-type PCF and a large-mode-area PCF [Fig.1(a)]. Passive mode-locking is achieved using saturable absorber mirrors (SAMs). We study the influence of the SAM parameters on performances obtained in this new class of fiber oscillators. The structures exhibit 20 % modulation depths and 500 fs relaxation time with resonant and antiresonant designs. The antiresonant SAM structures ensure absorption bandwidths 45 nm while the resonant structures exhibit 20 nm bandwidths. Stable mode locking with average powers as high as 15 μW at 15 MHz repetition rate, corresponding to microjoule energy level are obtained with all the structures. However, pulse properties and pulse shaping mechanism distinguish between resonant and antiresonant designs. Using a broadband antiresonant SAM leads to generation of highly-chirped pulses with 30 ps duration and 10 nm spectral width [Fig.1(b)]. The output pulses are extra-cavity dechirped down to 550 fs duration. By increasing the strength of the mode-locking mechanism through the combination of the SAM with the NPE process, we obtain shorter pulses with slightly boarder spectra. Indeed, the output pulse duration is decreased from 30 ps to 13 ps by adjusting the wave-plates settings. The dechirped pulse duration is then shortened to 450 fs. We note that the current laser performances are limited to 1 J by the available pump power. Using a resonant SAM structure, the output pulse duration is decreased to 7 ps [Fig.1(b)]. This pulse shortening results from the spectral filtering induced by the limited SAM bandwidth. All these results are in good agreement with numerical simulations which will be discussed in this communication. © 2011 IEEE

Sub-picosecond microjoule-class fiber lasers

We study the impact of the mode-locking mechanism on the performances of a microjoule-class all-normal dispersion fiber laser featuring large-mode-area photonic crystal fibers. © 2011 OSA

High-energy femtosecond photonic crystal fiber laser

We report the generation of high-energy high-peak power pulses in an all-normal dispersion fiber laser featuring large-mode-area photonic crystal fibers. The self-starting chirped-pulse fiber oscillator delivers 11 W of average power at 15:5 MHz repetition rate, resulting in 710 nJ of pulse energy. The output pulses are dechirped outside the cavity from 7 ps to nearly transform-limited duration of 300 fs, leading to pulse peak powers as high as 1:9 MW. Numerical simulations reveal that pulse shaping is dominated by the amplitude modulation and spectral filtering provided by a resonant semiconductor saturable absorber. © 2010 Optical Society of America

Femtosecond microjoule-Class ytterbium fiber lasers

We report the generation of 830 nJ energy from a mode-locked all-normal dispersion fiber laser featuring large-mode-area photonic crystal fibers. After external compression, 550 fs pulses with 1.2 MW peak power are demonstrated. © 2011 OSA

Diode-pumped ultrafast Yb:KGW laser with 56 fs pulses and multi-100 kW peak power based on SESAM and Kerr-lens mode locking

A high-power sub-60 fs mode-locked diode-pumped Yb:KGW laser based on hybrid action of an InGaAs quantum-dot saturable absorber mirror and Kerr-lens mode locking was demonstrated. The laser delivered 56 fs pulses with 1.95 W of average power corresponding to 450 kW of peak power. The width of the generated laser spectrum was 20.5 nm, which was near the gain bandwidth limit of the Yb:KGW crystal. To the best of our knowledge, these are the shortest pulses generated from the monoclinic double tungstate crystals (and Yb:KGW laser crystal in particular) and the most powerful in the sub-60 fs regime. At the same time, they are also the shortest pulses produced to date with the help of a quantum-dot-based saturable absorber. High-power operation with a pulse duration of 90 fs and 2.85 W of average output power was also demonstrated

High gain amplification up to 100 mJ to 3 J using Yb³⁺:YAG slab-based cat’s-eye cavities under variable seed and operating conditions

We demonstrate the optical architecture of a fairly compact design at 1030 nm for linear amplification, which enables the combination of very high gains and output energies in a single stage to be operated at room temperature. Gains and energies are experienced in the nanosecond regime up to 20 dB and 120 mJ, respectively, at the same time. This design makes use of a thick slab of Y b 3 + : Y A G in a scalable cat’s-eye cavity, provided there is uniform edge-pumping and fine control of a number of relevant spatial characteristics regarding the pump and the cavity. Highly variable operating conditions are considered for a comprehensive benchmark of the optical performance. They involve single 3 ns long seed pulses with an energy of 1 mJ, accordingly to more or less gain saturation, together with long bursts of stretched picosecond-long pulses. This gives access to kilowatt-class pulse trains of duration 3–5 ms, with a total energy of up to 3 J and an optical efficiency of 20%–25%, prior to more complete gain saturation.</jats:p