Table of contents

An effective supercontinuum (SC) generation is demonstrated by injecting picosecond self Q-switched mode-locked Nd:GdVO₄ laser pulses into a 1-m long microstructured fiber. The laser is operated at wavelength 100-nm away from the longer zero-dispersion of this dual zero-dispersion wavelength microstructured fiber. The phenomena of modulation instability, stimulated Raman effect, and dispersive wave can be sequentially observed from experimental results, leading to spectral broadening as pumping increases.

Dynamic multiphoton resonances in ultra-short super-intense laser pulses consisting of 50-200 field periods are considered numerically for a two-level system. The impact of non-resonant (Bloch-Siegert) and carrier-envelope effects on the dynamics of a two-level system was studied numerically, and conditions for complete population inversion were derived. The widths of multiphoton resonances increase with the increasing of the laser field. Results do not depend practically on the pulse duration. Effective resonance frequencies for multiphoton resonances increases strongly in a super-intense field. Multiphoton resonances are shifted and unified with each other in super-intense laser fields.

560 TW peak power has been achieved experimentally using a Cr:forsterite master oscillator at 1250 nm, a stretcher, three optical parametrical amplifiers based on KD*P crystals providing 38 J energy in the chirped pulse at 910 nm central wavelength, and a vacuum compressor providing 43 fs pulse duration. To our knowledge, it is a world-record OPCPA system and one of the five most powerful laser systems currently available.

On the base of the phase shifted fiber Bragg grating of 4 cm length written in the active non-PM Yb-doped fiber, a resonator with distributed feedback (DFB) has been formed. The single frequency single polarization unidirectional generation with the output power up to 4.5 mW has been obtained. The spectral and energy performances of the single frequency DFB fiber laser depending on the pump laser parameters and ways of pump wave coupling have been investigated. The competition between orthogonal polarization states has been also studied, and the single polarization regime of 0.5 mW power has been achieved.

A broadband hybrid two-stage fiber amplifier module, constructed of an erbium-doped fiber amplifier (EDFA) and a semiconductor optical amplifier (SOA) in series, is proposed and investigated experimentally. In the proposed amplifier, a short length erbium-doped fiber (EDF) was used in first stage for the pre-amplifier to increase the gain and reduce the noise figure. Therefore, the proposed hybrid amplifier not only enhances gain value, but decreases the noise figure. Moreover, the proposed amplifier can achieve 110 nm amplification bandwidth between 1500 and 1610 nm, when the entire gain are large than 11 dB and noise figure are less than 8 dB for -25 dBm input saturation power. Moreover, the performance of gain and noise figure in the proposed fiber amplifier has also been discussed.

A multi-wavelength erbium-doped fiber laser based on a Sagnac loop filter which is formed by a birefringent and highly nonlinear photonic crystal fiber (PCF), a 3-dB optical coupler and two polarization controllers is proposed. The PCF Sagnac loop filter is used as a comb filter and power-stabilizing and -equilibrizing component in the multi-wavelength erbium-doped fiber laser. Stable multi-wavelength lasing at room temperature is achieved, owing to the contributions of both the birefringent property and the four-wave mixing effect of the PCF.

The basic purpose of research was the creation of crystal fibers for application as temperature gauges for severe environments. Single crystal fibers of sapphire and YAG with sensitive zone doped by Cr ions were successfully grown up by the Laser Heated Pedestal Growth method. The results of temperature measurements are presented for a range 25-4000° C. Those temperature dependences of luminescence lifetime and spectra of Cr³⁺-ions in the crystal fibers are consistent with the data observed with bulk samples, being grown by Czochralski technique.

We report the delivery of high-energy nanosecond pulses (10 ns pulse width) from a Q-switched Nd:YAG laser through the fundamental mode of a hollow-core photonic crystal fiber at 1064 nm. At a pressure of 450 mbar, energies greater than 1 mJ were delivered in a single spatial mode through the hollow-core fiber, coupling efficiencies over 80% were demonstrated.

All-fiber Raman fiber source emitting at 1254 nm was realized. For the first time to pump Raman converter we have applied Yb:Bi pulsed fiber laser. The P-doped fiber was used as an active medium of the Raman converter. The conversion slope efficiency of 70% and the peak power of 12 W were observed.

Various fruit, vegetables and plants contain a high amount of carotenoids such as beta-carotene, lycopene, lutein, zeaxanthin, and other antioxidants in different concentrations and combinations. These substances used by nature are an effective defense mechanism against the destructive action of free radicals, which are the result of the negative influence of the environment. It was found that the peel of fruit and vegetables usually contains a higher amount of carotenoids than the pulp. Humans cannot synthesize carotenoids by itself, thus, they should be applied systemically with a supplementation rich in these substances. The diet, based on the consumption of a high amount of carotenoid rich products, increased the concentration of carotenoids in the human skin. Taking into consideration the results of previous studies, there is a strong correlation between the appearance of the skin concerning furrows and wrinkles and the level of carotenoid lycopene obtained in the skin. The present results demonstrate that a diet rich in products, which contain a high amount of carotenoids, can be an efficient strategy to reduce skin aging. In the present study, resonance Raman spectroscopy was used as a fast non-invasive optical method for the determination of the carotenoid antioxidant substances in fruit, vegetables and for the determination of the influence of a carotenoid rich diet on the antioxidant level of the human skin.

When the carious tissue is eliminated either by conventional methods (with burs) or with lasers, the risk of accidentally damage the surface of adjacent teeth may occur, which hypothetically could lead to a more susceptible surface for caries formation. This in vitro study aims to evaluate the caries resistance of the dental enamel surface irradiated by the Nd:YAG laser applied in conditions simulating accidental exposition. Thirteen third molars were used in this study. The experimental groups were: G1: sound control and control + carious; G2: contact Nd:YAG laser at 0.75, 1, 2, or 3 W; 10 Hz; 3 sec (27, 35, 71, and 106 J/cm²); G3: same parameters from G2 + caries artificial induction through the demineralization and demineralization (DES/RE) dynamic model. The caries resistance analysis was evaluated by the superficial morphological aspect through SEM images and also by Ca/P proportion through energy dispersive X-ray spectroscopy (EDX). The micrograph images showed that the Nd:YAG laser changed the normalmorphology of the enamel prisms resulting in a melted and re-solidified surface intensified with the power increase. Significant statistical differences were observed applying the Kruskal-Wallis statistical test (p ⩽ 0.01) among the Nd:YAG laser irradiated groups and the control with caries regarding the Ca/P proportion. As an exception, this was not observed when 3 W; 10 Hz; 3 sec; 106 J/cm² was applied and posteriously submitted to a cariogenic challenge. The results indicate that the Nd:YAG laser accidental irradiation at low power settings did not represent risks to the enamel caries resistance.

In the present study, the ability of a shampoo formulation containing caffeine as well as the fluorescent dye fluorescein to penetrate into hair follicles was investigated by in vivo laser scanning microscopy. A contact time of two minutes between the shampoo and the skin surface was sufficient for the formulation to penetrate deeply into the hair follicles and to remain there for up to 48 hours, even after washing. As hair follicles are surrounded by a close network of capillaries, dendritic cells and stem cells, they represent an important target for drug delivery. The results of the present study demonstrated that in vivo laser scanning microscopy is an efficient tool for the investigation of the dermatopharmacokinetics of topically applied molecules and their penetration pathways, as the method yields space- and time-resolved measurements.

Using normal rat liver we investigated the depth of necrosis induced by photodynamic therapy when different light doses and photosensitizer (Photogem®) concentrations. All experiments were done with a fluence rate of 250 mW/cm². Photosensitizer concentration was varied from 1.0, 1.5, 2.0, and 5.0 mg/kg of body weight and it was administered through the left tail vein. For each photosensitizer concentration the light dose was varied from 10, 50, 100, 150, and 200 J/cm². Each experimental point was done using five animals. The depth of necrosis analysis allows us to determine the threshold dose and compare its value with the existent results in the literature. Our result suggested a value about 3 times higher than the conventionally adopted value. It indicates the dependence of such value with the employed concentration photosensitizer.

The use of simple models to understand basic features of the PDT (Photodynamic Therapy) may contribute to the solid establishment of dosimetry in PDT enhancing its use in the clinical management of cancers and others lesions.

To present a new concept of outcome analysis after immediate reconstruction of traumatic lesions of the frontal branch of the facial nerve. With the aid of laser surface scanning, changes induced by frontal muscle contraction, i.e. frowning, in skin surface area on the forehead were measured in nine patients after repair of traumatic transection of the frontal branch of the facial nerve and in 10 healthy volunteers. With laser surface scanning analysis, consistent changes in surface area on the forehead were measured in both patients and healthy volunteers. Symmetry of 74±15% in forehead wrinkling was obtained 12 months after coaptation of the transected nerve. Laser surface scanning is a promising tool to assess outcome after repair of facial nerve laceration. It is easy to use, yields reproducible results and might be used in the future for other procedures.