Reflectivity of transient Bragg reflection gratings in fiber laser with laser-wavelength self-sweeping: erratum.

This erratum presents a correction to the computed reflection spectra of transient fiber Bragg gratings that are spontaneously built-up in the ytterbium-doped fiber of the fiber laser with laser wavelength self-sweeping. The corrected spectra have high reflectivity reaching values up to 100%. Therefore, they still more support the conclusion drawn in the original paper that self-sweeping is an important mechanism for triggering the self-Q-switched regime with giant pulse generation.

Reflectivity of transient Bragg reflection gratings in fiber laser with laser-wavelength self-sweeping.

We present a method for the estimation of the reflection spectra of transient gratings in rare-earth doped fiber lasers having a self-sweeping of laser wavelength. We show that high reflectivities of several tens of percent can be achieved. An example of this is demonstrated through the use of an experimental Yb-doped Fabry-Perot fiber laser. The gratings' spectra are highly asymmetric due to the apodization of the refractive index modulation. The importance of the self-sweeping regime for triggering self-Q-switched laser instabilities is discussed.

Fiber-optic pH detection in small volumes of biosamples.

Determining the pH values of microscopic plant samples may help to explain complex processes in plants, so it is an area of interest to botanists. Fiber-optic probes with small dimensions can be used for this purpose. This paper deals with the fiber-optic detection of the pH values of droplets of plant xylem exudate based on ratiometric fluorescence intensity measurements with an internal reference. For this purpose, novel V-taper sensing probes with a minimum diameter of around 8 µm were prepared that enable the delivery of fluorescence signal from the detection site on the taper tip to the detector. The taper tips were coated with pH-sensitive transducer (8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt; HPTS) and a reference [dichlorotris-(1,10-phenanthroline) ruthenium (II) hydrate (Ru-phen dichloride)] immobilized in a xerogel layer of propyltriethoxysilane and (3-glycidoxy)propyl trimethoxysilane. The prepared probes were sensitive to pH values mainly in the range from 6.0 to 9.0. In the pH range 6-9, the results were limited by measurement errors of about 0.2 pH units, and in the pH range 5-6 by measurement errors of about 0.5 pH units. Using the developed V-taper sensing probes, the pH values of in vivo and in vitro samples of small volumes (~6 µl) of exudate were measured. The results were validated by comparison with conventional electrochemical pH measurements.

Monitoring the growth and stress responses of yeast cells by two-dimensional fluorescence spectroscopy: first results.

S. cerevisiae growth and responses to different treatments were monitored by two-dimensional fluorescence spectroscopy, which simultaneously detects the fluorescence of a number of cells' own fluorophores. Growth curves of cultures of free cells were measured by means of tryptophan fluorescence in nonfluorescent culture medium and a flow-through system at a suitable excitation/emission beam geometry. Fast responses of the cells to anaerobic-aerobic transition or addition of glucose, methanol or cyanide, which could not be measured in this system because of the time delay inherent in transporting the cells from the culture flask to the cuvette, were monitored with cells immobilized in alginate. The major fluorescence changes caused by these treatments belonged to NAD(P)H which is a good indicator of the redox state of the cells.