Optical fiber laser induced fluorescence spectroscopy as a citrus canker diagnostic.

Citrus canker is a serious disease caused by Xanthomonas citri subsp. citri bacteria, which infects citrus plants (Citrus spp.) leading to large economic losses in citrus production worldwide. In this work, laser induced fluorescence spectroscopy (LIF) was investigated as a diagnostic technique for citrus canker disease in citrus trees at an orchard using a portable optical fiber based spectrometer. For comparison we have applied LIF to leaves contaminated with citrus canker, citrus scab, citrus variegates chlorosis, and Huanglongbing (HLB, Greening). In order to reduce the noise in the data, we collected spectra from ten leaves with visual symptoms of diseases and from five healthy leaves per plant. This procedure is carried out in order to minimize the environmental effect on the spectrum (water and nutrient supply) of each plant. Our results show that this method presents a high sensitivity (approximately 90%), however it does present a low specificity (approximately 70%) for citrus canker diagnostic. We believe that such poor performance is due to the fact that the optical fiber collects light from only a small part of the leaf. Such results may be improved using the fluorescence imaging technique on the whole leaf.

Electric field effects in the excitation of cold Rydberg-atom pairs.

In this work, we study the role of the ac Stark effects on the excitation of nS1/2 cold Rydberg atoms produced in a rubidium magneto-optical trap. We have observed an atomic population in the nP3/2 state after excitation of nS1/2 for 29

Detection of mechanical and disease stresses in citrus plants by fluorescence spectroscopy.

We have investigated the detection of mechanical and disease stresses in citrus plants (Citrus limonia [L.] Osbeck) using laser-induced fluorescence spectroscopy. Due to its economic importance we have chosen to investigate the citrus canker disease, which is caused by the Xanthomonas axonopodis pv. citri bacteria. Mechanical stress was also studied because it plays an important role in the plant's infection by such bacteria. A laser-induced fluorescence spectroscopy system, composed of a spectrometer and a 532 nm 10 mW excitation laser was used to perform fluorescence spectroscopy. The ratio of two chlorophyll fluorescence bands allows us to detect and discriminate between mechanical and disease stresses. This ability to discriminate may have an important application in the field to detect citrus canker infected trees.

PDT experience in Brazil: A regional profile.

The success of PDT and its establishment into the existent hall of therapeutic modalities depends on the collection of reported experiences from around the world. In that sense, it is important to report approaches taken by different countries and what their views are on the future of PDT. Following this idea, we present our clinical experience in photodynamic therapy (PDT) in Brazil, as well as the experimental advances coming up in parallel with clinical implementation. This report is a consequence of pioneering work in a collaborative program involving the Physics Institute in São Carlos, São Paulo State (SP), Brazil, the Medical School of the University of São Paulo, Ribeirão Preto, SP, Brazil and the Cancer Hospital Amaral Carvalho, Jaú, SP, Brazil. This collaborative program, begun in 1997, with the first patient treated in 1999, has treated over 400 patients by late 2004. About 80% of lesions were located in the head and neck or skin, but experience is being built in esophagus, bladder, gynecology, and cutaneous recurrence of breast cancer, among others. The overall results have shown to be compatible with previously reported data. Modifications, whose goal is to improve patient benefit and optimize results, are being implemented as we gain experience. In parallel with the clinical development, several laboratories have started studying experimental whose purpose is to analyze the clinical results and to contribute to the worldwide effort to bring PDT to the forefront of therapies offered to patients. We present the overall results of our 5 years experience as well as the whole implementation process.

Observation of ultracold ground-state heteronuclear molecules.

We report the observation of translationally ultracold heteronuclear ground-state molecules in a two-species magneto-optical trap containing 39K and 85Rb atoms. The KRb molecules are produced via photoassociation and detected by multiphoton ionization. We had characterized their temperature and measured their formation rate constant. We believe that the two-species trap could be used as a reliable source of ultracold molecules to be captured by electrostatic, magnetic, or optical traps. This possibility will certainly motivate further investigation of quantum collective effects as well as high-resolution spectroscopy of the rovibrational level structure of cold heteronuclear molecular systems.

Rydberg cold collisions dominated by ultralong range potential.

In this work we measure the time evolution of the population resulting from energy-transfer collisions as a function of the energy difference between the entrance and exit collisional channels using a sample of cold Rydberg atoms produced in a rubidium magneto-optical trap. The 34S(1/2) population, produced by collisions between atoms in the 33P(3/2) state, is monitored as a function of time through the pulsed-field ionization technique. The experimental results are compared with a recent published model based on a two-body interaction considering an attractive potential [Phys. Rev. A 65, 023405 (2002)]]; which is calculated according to a recent Letter by Boisseau et al. [Phys. Rev. Lett. 88, 133004 (2002)]]. The agreement is remarkable, which suggests the existence of such ultralong range potential proposed by Boisseau et al.

Spectral response for laser enhancement in hepatic regeneration for hepatectomized rats.

BACKGROUND AND OBJECTIVES: The low intensity laser therapy (LILT) has been widely used in all medical fields due to its therapeutic effects in reparative process, pain relief, and biostimulation. Even though there is a therapeutic window of wavelengths for clinical application, little has been done concerning the frequency spectrum response to biological effects. In this work, we investigate the dependence of different wavelengths irradiation in the enhancement of the tissue regeneration after partial hepatectomy in Wistar rats. STUDY DESIGN/MATERIALS AND METHODS: The proliferating cell nuclear antigen (PCNA) labeling index and the respiratory control (oxygen consumption in extracted mitochondria) were the tests used to evaluate the liver regeneration after laser irradiation with different wavelengths. RESULTS AND CONCLUSIONS: The results show a correlated spectral response that can be explained based on the combined effect of light penetration on biological tissues and the biomolecular excitation efficiency for each wavelength used.

Characterization of light penetration in rat tissues.

OBJECTIVE: The goal of this study is to determine the optical properties of different rat tissues with respect to spatial intensity variation and light distribution. We are interested mainly in the wavelength of 630 nm. Nevertheless, for liver tissue we have used 514 nm and 670 nm as well. BACKGROUND DATA: In the past, many articles have been written about the interaction of lasers with rat tissues. However, the technique of imaging the light distribution allows us to obtain the spatial scattering as well as an effective attenuation coefficient for the light intensity. METHODS: Slices of different rat tissues were placed between two microscope slide mounts (spaced by 3 mm). A laser beam was irradiated on the sandwiched tissue. A CCD camera placed on the side, orthogonal to the beam path, recorded the intensity distribution of the scattered light. Analysis of this spatial intensity profile allowed determining the variation of the intensity as the light penetrates the tissue. RESULTS: We have found that abdominal wall fat presents the lowest exponential decay when compared with liver, muscle, and kidney. The obtained values provided good data about the light distribution in those tissues when irradiated with a nondiffuse laser beam. For all tissues, we observed a spherical light distribution and exponential decay. Cirrhotic liver shows much stronger decay than healthy liver. These results are useful for several applications of laser for biostimulation a phototherapy.

Laser enhancement in hepatic regeneration for partially hepatectomized rats.

BACKGROUND AND OBJECTIVE: The bio-stimulation effect of laser has been observed in many areas of Medicine. However, there are a few works which investigate its use for liver regeneration. Most of their results were inconclusive due to the use of high power lasers. This work was carried out to investigate the bio-stimulation effect of laser in liver regeneration using low power lasers. STUDY DESIGN/MATERIALS AND METHODS: We used Wistar male rats, which were irradiated with laser light (wavelength 590 nm and intensity of 50 mW/cm(2)) for 5 minutes after 70% hepatectomy. The respiratory mitochondrial activity, the serum level of aminotransferase and the PCNA were measured. RESULTS: Our results show a dramatic increase in the mitochondrial activity for the laser treated group at 24 hours after the hepatectomy. CONCLUSIONS: We conclude that the laser promotes a bio-stimulation effect on the early stages of liver regeneration without any detectable damage of the cells.

Alternative to the hyperfine-change-collision interpretation for the behavior of magneto-optical-trap losses at low light intensity.

Usually, the large trap loss rates observed in MOTs at the low light intensity regime have been associated with hyperfine change collisions (HCC). We propose an alternative mechanism to explain the sudden raise up of trap loss rates at low intensity without relying on HCC. Using the Gallagher-Pritchard model [Phys. Rev. Lett. 63, 957 (1989)] together with an intensity dependent escape velocity, we were able to reproduce qualitatively well some existing experimental results, including recent observations by Nesnidal et al. [Phys. Rev. A 62, 030701(R) (2000)]. This result reopens the discussion in order to better understand the physical mechanisms and their actual contribution to the trap losses.