Water deficit and salt stress diagnosis through LED induced chlorophyll fluorescence analysis in Jatropha curcas L.

LED induced chlorophyll fluorescence analysis is employed to investigate the effect of water deficit and salt stress upon the growth process of Jatropha curcas L.. Red(Fr) and far-red(FFr) chlorophyll fluorescence around 685 nm and 735 nm, respectively, were observed and examined as a function of the stress intensity(salt concentration and water deficit). The fluorescence ratio Fr/FFr which is a valuable nondestructive and nonintrusive indicator of the chlorophyll content of leaves was exploited to monitor the jatropha plants under stress. The data indicated that salinity plays a minor role in the chlorophyll concentration of leaves for NaCl concentrations in the 25 to 200 mM range. The fluorescence ratio also permitted the detection of damage caused by water deficit in the early stages of the plants growing process. A significant variation of the Fr/FFr ratio was observed in the first 10 days of the experiment, and before signs of visual stress became apparent. The results suggest that the Fr/FFr ratio is an early-warning indicator of water deficit stress.

Solitons in the region of the minimum group-velocity dispersion of single-mode optical fibers.

Pulses launched with their central wavelength in the region of the minimum-dispersion wavelength of a single-mode optical fiber exhibit a distinct spectral splitting due to the nonlinearity. As a solitary wave evolves, the corresponding central wavelength of this component frequency downshifts while the dispersive wave is upshifted, in qualitative agreement with theoretical prediction.

Raman amplification of modulational instability and solitary-wave formation.

The effect of synchrohous Raman gain in a single-mode fiber on a weak signal exhibiting modulational instability is shown spectrally and temporally to give rise to the rapid development of a single ultrashort solitary wave and a lowlevel dispersive pedestal.

Suppression and manipulation of the soliton self-frequency shift.

Direct experimental evidence is presented that shows that in the presence of bandwidth-limited amplification, specifically, stimulated Raman scattering in a single-mode silica fiber, the self-frequency-shifting effect exhibited by solitons can be effectively suppressed.

Soliton generation through Raman amplification of noise bursts.

Operating in a high-gain regime, solitons with durations of the order of 600 fsec have been generated through the synchronous Raman amplification of noise bursts with durations of the order of 100psec and inverse bandwidths in the regime of the generated solitons.

Generation of 33-fsec pulses at 1.32 microm through a high-order soliton effect in a single-mode optical fiber.

Pulse shortening by a factor of 2700x at 1.32 microm has been realized by means of a two-stage pulse compression. In the first stage, 90-psec pulses from a cw mode-locked Nd:YAG laser were compressed to ~1.5 psec by using a standard fiber-grating-pair configuration. Subsequent propagation of these pulses through ~20 m of single-mode optical fiber with a minimum dispersion at 1.27 microm led to a final pulse width of 33 fsec. This represents the shortest reported pulse generated at 1.32 microm by using the technique described above as well as the largest overall compression factor using optical fibers yet reported.

High-efficiency single-pass solitonlike compression of Raman radiation in an optical fiber around 1.4 microm.

Highly efficient conversion (as great as 60%) into the broad first Stokes Raman band around 1.4 microm the 90-psec pump pulses from a cw mode-locked Nd:YAG laser at 1.32 microm has permitted, through a solitonlike compression mechanism in a single span of standard (lambda(0) = 1.3 microm) single-mode optical fiber, the generation of highly stable pulses of ~100 fsec, with average powers of ~30 mW in the solitary waves, which depend on fiber length and pump power.

Cross-phase modulation of incoherent light in single-mode optical fibers.

When two optical incoherent beams copropagate in an optical fiber, the intensity-dependent refractive index couples the two beams through a nonlinear process known as cross-phase modulation. We show, for the first time to our knowledge, experimental evidence on cross-phase-modulation-induced correlation time reduction and a concomitant growth of the frequency components of the two copropagating incoherent waves in a singlemode optical fiber. Theoretical analysis agrees well with experimental data.

Subpicosecond-pulse generation through cross-phase-modulation-induced modulational instability in optical fibers.

We report subpicosecond-pulse generation at 1.319 microm in a single-mode optical fiber by modulational instability induced through cross-phase modulation by 1.06-microm pulses propagating in the normal dispersion regime. Pulse-repetition rates approaching 300 GHz were achieved.

2.3-ps pulses from a Kerr-lens mode-locked lamp-pumped Nd:YLF laser with a microdot mirror.

Pulses as short as 2.3 ps have been generated by passive mode locking of a lamp-pumped Nd:YLF laser with a microdot mirror mode locker for Kerr-lens mode-locking (KLM) saturable absorber action and a compact Gires-Tournois interferometer for dispersion compensation. KLM was initiated with an acousto-optic modulator. Average output powers of 800 mW have been achieved. This result demonstrates the potential use of KLM for generating near-bandwidth-limited pulses from high-power lamp-pumped sources.

Two-photon-resonant photoinduced second-harmonic generation in Er(3+)-doped germano-aluminosilicate optical fibers pumped at 1.319 microm.

The growth of a two-photon-resonant photoinduced second-harmonic signal at 660 nm in Er(3+)-doped GeO(2)-Al(2)O(3)-SiO(2) single-mode optical fibers pumped by a Nd:YAG laser at 1.319 microm is reported. Defect states in the band gap are optically excited through a resonant two-photon absorption process connecting the (4)I(15/2)-(4)F(9/2) energy levels of the erbium ions present in the fiber core. As a result a periodic X((2)) grating is formed, and efficient second-harmonic generation takes place. For erbium-free GeO(2)-doped silica test fibers no second-harmonic signal has been detected, even after hours of seeded preparation process.

Cascade Raman soliton fiber ring laser.

Pulses as short as 200 fsec at 1.5 microm and 230 fsec at 1.6 microm have been generated through a cascade Raman, solitonlike process in a fiber ring oscillator. A dispersion-shifted (lambda(0) = 1.46 microm) single-mode fiber was used as the gain medium, which was synchronously pumped by a cw mode-locked Nd:YAG laser operated at 1.32 microm.

Fourfold output power enhancement and threshold reduction through thermal effects in an Er(3+)/Yb(3+)-codoped optical fiber laser excited at 1.064 mum.

Thermally induced output power enhancement and threshold reduction in an Er(3+)/Yb(3+) -codoped optical fiber laser at 1.54mum pumped by 1.064-mu;m cw radiation is demonstrated. Steady fourfold output power increase and threshold decrease were achieved by heating of the Yb(3+) -sensitized Er(3+) -doped fiber laser medium in the temperature range 23-150 degrees C degrees . The laser efficiency thermal behavior is assigned to the temperature-dependent effective absorption cross section of the ytterbium sensitizer through the so-called multiphonon-assisted anti-Stokes excitation process.