Vector vortex beams generated by q-plates as a versatile route to direct fs laser surface structuring

We report an experimental investigation on direct laser surface structuring with femtosecond vector vortex beams generated by means of q-plates with topological charges q = 1, 3/2, 2, 5/2. Structured light beams with spatially variant state of polarization and intensity are generated and applied to multi-pulse irradiation of a solid crystalline silicon target. The creation of a variety of surface structures, like laser induced periodic surface structures, multi-spot arrays and shaped ablation craters, is demonstrated by direct laser surface structuring with vector vortex beams at different values of q. The features of the surface structures are compared with the vector vortex beam characteristics at the focal plane, evidencing their relationship with the polarization and intensity profile of the laser beams. Our experimental findings show that vector vortex beams produced by q-plates can offer a valuable and versatile route to imprint unconventional surface structures on a solid target through a mask-free ablative process and step scan processing

Surface structures with unconventional patterns and shapes generated by femtosecond structured light fields

We present an investigation on ultrashort laser surface structuring with structured light fields generated by various q-plates. In particular, q-plates with topological charges q = 1, 3/2, 2, 5/2 are used to generate femtosecond (fs) vector vortex beams, and form complex periodic surface structures through multi-pulse ablation of a solid crystalline silicon target. We show how optical retardation tuning of the q-plate offers a feasible way to vary the fluence transverse distribution of the beam, thus allowing the production of structures with peculiar shapes, which depend on the value of q. The features of the generated surface structures are compared with the vector vortex beam characteristics at the focal plane, by rationalizing their relationship with the local state of the laser light. Our experimental findings demonstrate how irradiation with fs complex light beams can offer a valuable route to design unconventional surface structures

Surface micro-structuring with ultrashort laser pulses

The field of laser ablation was born with the invention of laser and it did not take long to be present in a variety of applications. The number of studies in this field grew very fast and it became increasingly more popular for manufacturing, chemical analysis, biology, medicine and so on. For many years the researchers explored the basic scientific understanding of the involved processes, meanwhile improving the instrumentations used and expanding the type of laser sources. With the advent of femtosecond (fs) pulse lasers the interests in laser-solid irradiation and ablation moved towards the use of ultrashort light pulses. Among the various phenomena involved in the interaction of ultrashort laser pulses and solid targets, the appearance of tiny reproducible surface patterns made this field much more popular and of interest also for technological and industrial applications. This thesis explores the formation of fs laser induced periodic surface structures (LIPSS), their morphological features, possible ways to control them by exploiting the influence of experimental parameters (wavelength, polarization, energy, etc. of the laser pulses) and illustrates few examples of interest for possible applications. The surface morphologies were fabricated experimentally and analyzed by different imaging characterization techniques using as targets silicon and copper plates as well as gold thin film on a silicon substrate. The thesis starts with a brief introductory chapter (Chapter 1) presenting the history of this innovative field of research, fs laser surface structuring. In addition, the essential models and theories along with experimental approaches used to realize the LIPSS and investigate their formation mechanisms are also summarized. Chapter 2 illustrates the experimental setups and techniques used to carry out the experiments as well as methods for the measurement of physical parameters such as threshold fluence and spot size of the laser beams exploited in the course of the thesis, namely the Gaussian and the vector vortex beams. In particular, the standard Gaussian beam and the vector vortex more complex spatial intensity profiles are considered. The optical vector vortex beams are generated by using a beam converter based on a q-plate that modifies the original Gaussian beam. The complex spatial structure of the state of polarization and shape of these complex light fs laser beams when fired on a silicon substrate, in air, allows producing very complex LIPSS patterns and shaped craters, as discussed in Chapter 3. The characteristics of such surfaces and the possibility to fabricate unconventional surfaces are discussed in detail. So far, the formation mechanisms of LIPSS with sub-wavelength spatial period, named as ripples, are well established. Within the framework of this thesis, I tried to gain more information on the physical processes involved in the generation of LIPSS with supra-wavelength period, named grooves, on a silicon target. In Chapter 4, the influence of experimental parameters like laser pulse repetition rate, laser wavelength and ambient pressure on the surface structures with special emphasis on the grooves is addressed. The results evidence that the appearance of “grooves” is very much dependent on the experimental conditions and provide in some cases (namely, low ambient pressure and high repetition rate) information that can be useful to unveil certain mechanisms involved in supra-wavelength LIPSS formation. Finally, in Chapter 5, I summarized results of experiments carried out on other materials, e.g. copper plate and gold thin film on silicon substrate, in the course of my thesis work. The main aim here is on the possibility of modifying the response of the material through laser processing. As a first example, texturing of copper surfaces, through scanning of the fs laser beam in ablation regime, brought up very interesting surface features composed of induced ripples and random oriented nanoparticles. The manufactured copper surfaces showed a degree of freedom in controlling the wetting response of the material. The second example concerns the possibility to fabricate two-dimensional THz metasurfaces by means of the mask-free fs laser surface structuring technique. The THz transmission response of the realized samples was measured in a collaborating laboratory and showed a good agreement with simulation addressing the possibility to design and realize such kind of THz optical components. Finally, preliminary experiments were carried out on CdZnTe, a direct and wide band gap ternary semiconductor alloy of possible interest for room-temperature detection of nuclear-radiation and infrared light and for which fs laser surface structuring has been scarcely investigated to date. To conclude, the observations based on the experiments carried out in the course of this thesis provide valuable and interesting results for supporting this challenging field of research supporting a deeper understanding and a larger control on the laser induced surface structures

Investigated inhibitory effect of aqueous extract of pistachio leaf (Pistacia atlantica) on the isolates of pathogenic Escherichia coli and Candida albicans from urinary and vaginal samples

Background and Aims: Pistacia atlantica is one of the medicinal plants native to Iran and known for its antimicrobial properties. Therefore, the present study aimed to investigate the antibacterial and antifungal effects of the aqueous extract of P. atlantica leaves on clinical isolates of Escherichia coli and Candida albicans in vivo. Materials and Methods: In this descriptive-cross-sectional study, the minimum inhibitory concentration (MIC) and minimum bactericidal/ fungicidal concentration (MBC/MFC) of aqueous extract of pistachio leaf were determined on 60 isolates of E. coli and 60 isolates of C. albicans, according to CLSI protocol at concentrations of 0.125-100 mg/ml. The obtained results were analyzed using R software at a significance level of 0.05. Results: The mean minimum inhibitory concentrations of coriander extract for E. coli and C. albicans clinical isolates were obtained at 45.3±1.0 and 43.7±1.1 mg/ml, respectively. The comparison of the minimum concentration of growth inhibitor and lethality of clinical isolates with standard E. coli strain was not significantly different (P=0.65); nonetheless, the standard strains of C. albicans were significantly different from the clinical isolates of this fungus (P<0.001). Conclusion: As evidenced by the results of the present study, the aqueous extract of P. atlantica leaves has inhibitory effects on the clinical isolates of E. coli and C. albicans. Therefore, it is possible to use the aqueous extract of this plant in isolation or in combination with other drugs to treat urinary tract and vaginal infections

Epidemiological and clinical profiles of acute poisoning in patients admitted to the intensive care unit in eastern Iran (2010 to 2017)

Abstract Background Acute poisoning is a common chief complaint leading to emergency department visits and hospital admissions in developing countries such as Iran. Data describing the epidemiology of different poisonings, characteristics of the clinical presentations, and the predictors of outcome are lacking. Such data can help develop more efficient preventative and management strategies to decrease morbidity and mortality related to these poisonings. This manuscript describes the epidemiology of acute poisoning among patients admitted to the intensive care unit (ICU) in Birjand, Iran. Methods This retrospective, cross-sectional study was conducted to characterize acute poisonings managed in the ICU during a 7-year period from March 2010 to March 2017 in a single center in Birjand, Iran. Patient characteristics, suspected exposure, the route of exposure, and outcome data were collected from hospital medical records. Results During the study period, 267 (64% male and 36% female) patients met inclusion criteria. Pharmaceutical medication (36.6%), opioids (26.2%) followed by pesticides (13.9%) were the most common exposures 38.2% of these cases were identified as suicide attempts. There were different frequencies in terms of xenobiotic exposure in relation to gender (p = 0.04) and the survival (p = 0.001). There was a significant difference between various xenobiotics identified as the cause of poisoning (p = 0.001). Mortality rate in our study was 19.5%. The incidence of outcomes was significantly higher in patients poisoned with opioids, pesticides, benzodiazepines, and tricyclic antidepressants (p < 0.05). The median length of hospital stay was higher in pesticide-poisoned patients (p = 0.04). Conclusion Opioids and pesticides were the most common exposures. The mortality rate of the poisoned patients in the ICU was proportionately high. The mortality rate due to opioid poisoning is a major concern and the most significant cause death due to poisoning in the region. Further monitoring and characterization of acute poisoning in Birjand, Iran is needed. These data can help develop educational and preventative programs to reduce these exposures and improve management of exposures in the prehospital and hospital settings

Effects of ambient air pressure on surface structures produced by ultrashort laser pulse irradiation

We report an experimental analysis addressing striking effects of residual air ambient pressure, from atmospheric conditions (103  mbar) to high vacuum (10-4  mbar), on the surface structures induced on a silicon target by direct femtosecond laser irradiation. We observe an interesting direct impact of the ambient pressure on the period and depth of the generated ripples as well as on the formation of microgrooves. Moreover, a significant correlation is observed between the ripples' period and depth. The change of pressure is accompanied by a variation of the degree of nanoparticle coverage, which is eventually recognized as an important factor for the development of the final surface structures. These results shed light on the intriguing mechanisms underlying the formation of the various surface textures, also evidencing that the ambient pressure can act as an effective parameter to tailor some characteristic features of the processed surface

Laser surface texturing of copper and variation of the wetting response with the laser pulse fluence

We report an experimental investigation on laser surface texturing of copper targets by Ti:Sa femtosecond laser pulses addressing their wetting response to water droplets. In particular, fs laser surface processing is used to developed hierarchical surface structures by writing parallel micro-trenches with a period of 50 μm at different laser pulse fluences. The laser irradiation simultaneously induces both the formation of laser induced periodic surface structures (LIPSS), in form of periodic ripples, and the random decoration with nanoparticles, resulting in the formation of a multiscale surface morphology. The morphological features of the samples are investigated and correlated with their wetting response through static contact angle measurements. Our findings evidence a progressive increase of the contact angle with the laser pulse fluence. The combination of the microscale trenches, written by laser line scanning, with the ripples patterns and the random nanoparticles decoration, formed on the surface, allow developing highly hydrophobic copper samples with contact angles reaching values around 160°, presenting potential interest for wettability applications