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Numerous studies focus on cancer therapy worldwide, and although many advances have been recorded, the complexity of the disease dictates thinking out of the box to confront it. This study reviews some of the currently available ionizing (IR) and non-ionizing radiation (NIR)-based treatment methods and explores their possible combinations that lead to synergistic, multimodal approaches with promising therapeutic outcomes. Traditional techniques, like radiotherapy (RT) show decent results, although they cannot spare 100% the healthy tissues neighboring with the cancer ones. Targeted therapies, such as proton and photodynamic therapy (PT and PDT, respectively) present adequate outcomes, even though each one has its own drawbacks. To overcome these limitations, the combination of therapeutic modalities has been proposed and has already been showing promising results. At the same time, the recent advances in nanotechnology in the form of nanoparticles enhance cancer therapy, making multimodal treatments worthy of exploring and studying. The combination of RT and PDT has reached the level of clinical trials and is showing promising results. Moreover, in vitro and in vivo studies of nanoparticles with PDT have also provided beneficial results concerning enhanced radiation treatments. In any case, novel and multimodal approaches have to be adopted to achieve personalized, enhanced and effective cancer treatment.

The discovery of coherent laser light in 1960 shifted and expanded the biomedical applications of radiation to the non-ionizing part of the electromagnetic spectrum. As in the case of ionizing radiation, but considering the laser specific features, the effective, safe and ethically acceptable use of biomedical laser technology requires interdisciplinary collaboration between physicists, engineers and physicians. This should extend at the research, preclinical and clinical level, inspiring at this time the dynamic discipline of Medical Physics in new areas. With this work we aim to introduce the interested reader in the need of dosimetry in medical applications of laser radiation, as this field is still unexplored. After some necessary definitions, we give a brief review of the basic biophysical mechanisms of coherent light-matter interactions. The manuscript focuses on biomedical laser applications in diagnosis and therapy (i.e. in Theranostics). From the vast field of laser theranostic applications we have chosen some experimental and theoretical results - examples of quantification of the laser effect, particularly relevant to soft and hard tissue laser ablation, laser induced photodiagnosis and photodynamic therapy of cancer. These topics intend to highlight the important role of Medical Physicists in the optimization of well-established laser based clinical procedures and mainly emerge the necessity of the relevant dosimetry for each application. Finally, we hope that this effort is going to give food for thought and highlight the importance of deep knowledge of the physics behind some everyday medical applications.

The necessity for decentralization of diagnostic technology, from a biomedical laboratory to near the patient sites, has driven the research community to engage the new generation smartphones with novel diagnostic and detection platforms. In this work, we will use state-of-the-art knowledge and state-of-the-art technology to construct an innovative platform on mobile devices with a future outlook of in vivo intervention. Specifically, we have built a low-cost smartphone-based microscopy technique by applying optics principles. With this technique we revealed the ability to identify PMMA beads circulating in a microfluidic channel, comparing its performance with the results obtained with an optical trapping device. The proposed platform could act as a detection and image analysis station for rapid and sensitive imaging of human cell collections from body fluids (biomedical diagnosis) or for screening of the water quality in remote areas (environmental pollution monitoring).

In oncology, cancer radiotherapy is a well-established therapeutic technique for more than 100 years and, worldwide, about two-thirds of all cancer patients will undergo conventional X-rays or gamma-rays therapy, as monotherapy or as part of their treatment, to destroy tumor cells by damaging their DNA. As the high energy electromagnetic waves based radiotherapy is not equally effective in all types and location of cancerous tumors, radiotherapy using accelerator based hadron beams is a well-established alternative, especially for deep-placed tumors, as a result of the well-known Bragg peak phenomenon. External proton beam radiation therapy is most commonly used in the treatment of pediatric, central nervous system and intraocular cancers. To overcome the major obstacle of the very expensive proton production facilities (through accelerators) in building of proton cancer treatment medical centers, the use of high-power lasers for particle radiation production was proposed. The recent development of lasers with ultrashort pulses (e.g. with pulse lengths around 30 fs) resulted in particle acceleration from the rear side of a laser-irradiated thin foil, based on their unique properties and laser-matter interaction mechanisms. In this review work, we aim to present the progress toward laser-driven radiotherapy, as well as to discuss if and how the radiobiological effectiveness of particle radiation generated by lasers differs from that provided by other conventional techniques. We will discuss the expectations and limitations in anti-cancer laser-driven proton therapy, reported in literature over the last decade. In the framework of the national project HELLAS-CH, we will present some of the preliminary efforts on the combined photodynamic and ionizing radiation action, with ultra-fast laser pulses, on tissue simulators and biological samples.

The introduction of new upconverting nanoparticles (UPCNPs) in the tumor area is being investigated worldwide as a solution for deep tissue theranostics interventions. Moreover, as the development of biophotonics techniques permits bioimaging in nanoscale, both photodynamic and photothermal sensing should be achieved even at cellular level with minimum perturbation, i.e., in absence of any physical contact between cells and sensing units at a single-cell level via optical tweezers. In our work, we discuss the biophotonic upconversion mechanism of nanoparticles’ excitation/emission at cellular level, under laser trapping conditions, via considering laser radiation of NIR (specifically at λ = 808 nm) for optimal penetration in biological tissues. Moreover, a theoretical simulation model will be presented for evaluation of the electric field distribution in optically trapped particles. Water soluble UPCNPs with maximum absorbance wavelength at λ = 808 nm and emission at 545 nm and 660 nm will be studied. The photoluminescence of biocompatible UPCNPs could provide a promising powerful tool for PDT single-cell analysis and/or for photothermal enhancement and sensing in an optical tweezers’ platform.

Photodynamic therapy (PDT) is a non-invasive procedure mainly used for treatment of malignancies. It is based on cytotoxic products generation after the excitation of absorbed photosensitizing drugs by non-ionizing radiation. The wavelength chosen is usually in the 620 - 700 nm region, resulting in limited tissue penetration depth. The relatively low irradiance values and the treatment time that, in most cases, lasts for a few minutes result in limited photothermal effects, which are usually overlooked. Therefore, in this study we computationally assess the temperature distribution during PDT in a cancer bearing mouse model. A user-friendly application is created that could be used in the treatment planning step of PDT. It receives as input various parameters, such as laser power, beam radius, irradiation time, body temperature and returns the maximum tissue temperature and irradiance values. Furthermore, it offers visualization of the generated effects through the spatial distribution of temperature, irradiance, acute necrosis and damaged tissue percentage that are presented in the form of interactive 3D plots. The conducted simulations reveal that 43 °C, which are in the hyperthermia range, are difficult to be excessed in PDT clinical practice, although topical thermal effects are observed.

As one of the major health problems for mankind is cancer, any development for the early detection and effective treatment of cancer is crucial to saving lives. Worldwide, the dream for the anti-cancer procedure of attack is the development of a safe and efficient early diagnosis technique, the so called “optical biopsy”. As early diagnosis of cancer is associated with improved prognosis, several laser based optical diagnostic methods were developed to enable earlier, non-invasive detection of human cancer, as Laser Induced Fluorescence spectroscopy (LIFs), Diffuse Reflectance spectroscopy (DRs), confocal microscopy, and Optical Coherence Tomography (OCT). Among them, Optical Coherence Tomography (OCT) imaging is considered to be a useful tool to differentiate healthy from malignant (e.g. basal cell carcinoma, squamous cell carcinoma) skin tissue. If the demand is to perform imaging in sub-tissular or even sub-cellular level, optical tweezers and atomic force microscopy have enabled the visualization of molecular events underlying cellular processes in live cells, as well as the manipulation and characterization of microscale or even nanoscale biostructures. In this work, we will present the latest advances in the field of laser imaging and manipulation techniques, discussing some representative experimental data focusing on the 21th century biophotonics roadmap of novel diagnostic and therapeutical approaches. As an example of a recently discussed health and environmental problem, we studied both experimentally and theoretically the optical trapping forces exerted on yeast cells and modified with estrogen-like acting compounds yeast cells, suspended in various buffer media.

Measurement of the transmission laser radiation from Q-switched and free-running Er:YAG lasers operating at 2.94 μm through fluoride glass multimode optical fibers of 448, 465 and 620 μm core diameter were performed. Attenuation measurements were obtained as a function of the laser energy input, of the bending angle and of the radius of curvature. The fibers exhibited low attenuation under straight and bent conditions. The output beam quality was also studied using the appropriate beam profiler. The output beam profiles showed a central multi-spiked energy distribution.

Microfluidic devices provide a platform with wide ranging applications from environmental monitoring to disease diagnosis. They offer substantive advantages but are often not optimized or designed to be used by nonexpert researchers. Microchannels of a microanalysis platform and their geometrical characterization are of eminent importance when designing such devices. We present a method that is used to optimize each microchannel within a device using high-throughput particle manipulation. For this purpose, glass-based microfluidic devices, with three-dimensional channel networks of several geometrical sizes, were fabricated by employing laser fabrication techniques. The effect of channel geometry was investigated by employing an optical tweezer. The optical trapping force depends on the flow velocity that is associated with the dimensions of the microchannel. We observe a linear dependence of the trapping efficiency and of the fluid flow velocity, with the channel dimensions. We determined that the highest trapping efficiency was achieved for microchannels with aspect ratio equal to one. Numerical simulation validated the impact of the device design dimensions on the trapping efficiency. This investigation indicates that the geometrical characteristics, the flow velocity, and trapping efficiency are crucial and should be considered when fabricating microfluidic devices for cell studies.

Background/purpose: Laser-induced autofluorescence spectroscopy provides excellent possibilities for medical diagnostics of different tissue pathologies including cancer. However, to create the whole picture of pathological changes, investigators collect spectral information from patients in vivo or they study different tumor models to obtain objective information for fluorescent properties of every kind of healthy and diseased tissue. Therefore, it is very important to find the most appropriate, and close to the human skin, animal samples from the fluorescence point of view, which will allow the extrapolation of the animal data to human spectroscopic diagnostics. Methods: In the present work, we examined the autofluorescence properties of different animal skin tissues, which are considered as the most common skin models. A nitrogen laser was used as an excitation source. Samples of healthy mouse, chicken and pig skin in vivo and/or ex vivo were studied and were compared with results obtained from investigations of healthy human skin in vivo. Results and conclusion: Specific features of the recorded spectra are discussed and the possible origin of the obtained fluorescence signals is proposed. Quantitative evaluation of data extrapolation for each skin type is also depicted.

Two different kinds of chalcogenide glass IR fibers were evaluated relative to transmission of pulsed IR radiation produced by several laser sources in the wavelength range from 1 to 10 μm. Fibers composed either from As–Se–Te or from As 2 S 3 glass, of 250, 500, 750 and 1000 μm and 250, 750 and 1000 μm core diameters were studied, respectively. Attenuation measurements were obtained as a function of the laser energy input and as a function of curvature, wherever this was possible. The output beam quality was also studied using a beam profiler. The lasers used were a Q-switched Nd:YAG laser, emitting at 1.06 μm, a free-running or Q-switched Er:YAG laser emitting at 2.94 μm and a tunable pulsed CO 2 laser emitting in the range of 9.3–10.6 μm. The fibers exhibited better behavior when tested with the Er:YAG laser and they were found fragile in pulsed radiation from the Nd:YAG and the CO 2 laser. The output beam profiles generally showed a central multi-spiking energy distribution.

The field of optical trapping has dramatically grown due to implementation in various arenas including physics, biology, medicine and nanotechnology. Certainly, optical tweezers are an invaluable tool to manipulate a variation of particles, such as small dielectric spheres, cells, bacteria, chromosomes and even genes, by highly focused laser beams through microscope. As the main disadvantage of the conventional optical trapping systems is the diffraction limit of the incident light, plasmon assisted nanotrapping is reported as a suitable technique for trapping sub-wavelength metallic or dielectric particles. In this work, firstly, we report briefly on the basic theory of plasmon excitation, focusing on the interaction of nanoscale metallic structures with laser light. Secondly, experimental and numerical simulation results are also presented, demonstrating enhancement of the trapping efficiency of glass or SiO2 substrates, coated with Au and Ag nanostructures, with or without nanoparticles. The optical forces were calculated by measuring the particle’s escape velocity calibration method. Finally, representative applications of plasmon assisted optical trapping are reviewed, from cancer therapeutics to fundamental biology and cell nanosurgery.

Biomedical laser light dosimetry relies on spatial light distribution measurements in combination with the appropriate laser–tissue interaction model that may be used to determine the tissue optical coefficients and the fluorophore concentration from its fluorescence spectra. Therefore, modelling of light transport in tissue, for optimization of laser dosimetry, requires the development of simple theoretical models and the experimental implementation in tissue-simulating phantoms, with known optical and fluorescence properties. Low cost phantoms were used, based on agar dissolved in water as the transparent matrix. The latter is loaded with various amounts of Intralipid and fluorophores as light scatterer and absorbers, respectively. The optical properties of these phantoms were measured at two different visible wavelengths. By comparing the fluorescence emission spectra of the turbid samples containing the same fluorophore in different concentrations, we can calculate the concentration. In addition, the evaluation of the scattering and absorption coefficients allow us to predict the spatial distribution of the light intensity inside and outside of the phantom. It seems that the Monte Carlo simulation is an effective and relatively simple mathematical approach for tissue optical properties evaluation.

Twenty-one teeth with one root canal were prepared by the step-back technique, divided into three groups, and split longitudinally. Group A served as a control. In group B, 20 to 150 pulses of 100 micros, 30 to 70 mJ per pulse at 1 to 4 Hz from a free-running Er:YAG laser were applied to the root-canal dentin. In group C, the Q-switched Er:YAG laser, with the same energy parameters and a 190-ns pulse duration was used. Scanning electron microscopy examination revealed that control specimens had debris and smear layer obscuring the dentinal tubules at all levels in the canals without crack formation. Both groups of laser-treated dentin were clean with opened dentinal tubules except around the lased area in which there was an intact smear layer. Cracks were observed in both laser groups with higher frequency in group C. In group B, craters with different depth levels at the root canal walls were produced and the energy apparently was distributed equally, because craters were well-shaped. In contrast, the ablation efficiency in group C was questionable with the parameters used in this study. Consequently, suitable parameters of the free-running Er:YAG laser must be found before its careful use as an adjunct in endodontic therapy.

The stimulated Raman scattering (SRS) beam spatial mode structure is studied in H2 and D2 gases, in a 60 cm-long high-pressure Raman cell, using a pulsed Nd:YAG laser at 266 nm. The conversion efficiencies of the first and second Stokes in H2, D2 and H2/D2 mixtures have been measured precisely in the 1–14 atm range. The SRS beam profiles were recorded for different gas pressures in the high-pressure Raman cell and interesting behaviour is revealed. Homogeneous SRS spatial profiles were obtained only for pressures higher than 7 atm. For lower pressures the profiles are either in the form of a ring or of a more complicated shape. The results are explained in terms of nonlinear self-focusing processes during the pump beam propagation in the Raman cell. Also, from our measurements, a more precise value of the nonlinear index of refraction for the H2 and D2 at 266 nm is proposed.

Potassium 4S1/2–6S1/2 two-photon excitation initiates the emission of several internally generated photons. For the first time two emission lines, one close to and one below the potassium 4P3/2 level, are reported for low pumping intensity. Radiation emitted below the 4P3/2 level is due to a parametric four-wave mixing process that uses the photons emitted at the 5P3/2–4S1/2 transition and a two-step four-wave mixing process generates the line emitted close to the 4P3/2 level.

Resumen del trabajo presentado en el International Multidisciplinary Microscopy Congress (INTERM2013), celebrado en Antalya (Turquía), del 10 al 13 de octubre de 2013, Micromanipulation of dielectric objects, from polystyrene spheres to living cells, is achieved when radiation pressure forces create stable trapping by highly focused laser beams through microscopes. However, the impressive history of optical trapping is shadowed by the light diffraction limit, as research currently has focused on materials below the micron scale, requiring stronger optical confinement and higher intensities than can be provided by the conventional optical tweezers. Recently, plasmonic nanostructures have entered the field, either to assist or enhance it. In this study, we present experimental results on using localized fields of metallic structures for efficient trapping, with various patterns (dots, fringes and squares). The patterns were produced by laser interferometry on almost continuous Ag or Au films on glass and glass covered by an amorphous Al2O3 layer (10 nm thick) respectively. We have calculated the optical forces by measuring the particle’s escape velocity. The results show that the effective quality factor Q in the patterned metal film is enhanced by a factor >10, with respect to the unpatterned metal film and a factor >100, with respect to an uncoated glass. In addition, mathematical simulation of plasmonic fields is investigated to confirm and explain theoretically, the experimentally observed plasmonic enhancement., RP acknowledges a grant from the JAE-doc program co-funded by European Social Fund. This work has partially been supported by MAT2011-28345-C02-02 (Spain) projects.

Quasi-simultaneous laser action in the UV (0.337 μm ) and the IR (10.6 μm ) was observed from a pulsed laser with a sliding discharge plasma cathode. The laser operates at atmospheric pressure, with a gas mixture of CO2/N2/He, at a 0.26/0.50/4.0 l min −1 flow rate. Output energies of 30 mJ in the IR and 0.35 mJ in the UV were obtained, from a laser discharge volume of 38.0×1.0×2.8 cm 3 . The optimum gas mixtures have been determined and the temporal behavior of the discharge parameters, the performance characteristics of the laser and the beam spatial distributions were investigated.

The interaction of picosecond laser radiation with human dental tissue was investigated in this study, in order to determine the ablation rates and the surface characteristics of the dentine by using scanning electron microscopy (SEM). Dentine ablation was performed by using tooth sections of different thicknesses (0.5–2.0 mm). Dental tissue samples were irradiated in air with the fundamental wavelength and first harmonic of a regenerative amplifier Nd:YAG laser system, at 1064 nm and 532 nm, respectively, with a pulse duration of 100 ps and a pulse repetition rate of 10 Hz. The results showed very clean craters surrounded by minimum melting of the surface of dentine when the 1064 nm pulses were used. In contrast, when the first harmonic 532 nm pulses were used, the SEM examinations revealed cracks and melting of dentine with irregular surface modification. Consequently, it seems that cleaning and shaping of the root canal walls during endodontic therapy with the picosecond Nd:YAG laser application may be possible in the future. The, as yet unexplored, field of the picosecond laser interaction with hard dental tissue is expected to be a potential alternative for powerful laser processing of biomedical structures.

), deuterium (D2), and mixtures of hydrogen and helium (H2/He), versus Raman gas pressure and input pump energy of the pulsed Nd:YAG laser at 355 nm, are reported. Photon conversion efficiencies of 50% and 27% are achieved at the first Stokes lines (S1) in H2 and D2, respectively. As a result, ultraviolet and visible laser light (274–503 nm) was generated with energies ranging from a few mJ up to several tens of mJ.

A circuit and discharge simulation is presented for a TEA HF laser operating with a He/SF 6 /C 3 H 8 gas mixture. A comparison of the simulated discharge voltage, current, resistance and input power with the corresponding experimental results is presented together with a discussion on the factors affecting the simulation accuracy.

A model of thermal laser ablation of soft tissues is developed taking into consideration two mechanisms: evaporation and liquid moving, due to vapour pressure gradient. Usually a soft tissue is modelled as a single-component material with thermal and optical properties very similar to those of water. We examined the non-stable kinetics of the evaporation process, for short-pulse infrared laser ablation of soft tissues, and we also calculated the average liquid velocity and the ablation rates under vapour pressure gradient. The theoretical results are in good agreement with previous reported experimental data on gelatin and polyacrylamide tissue phantoms

The ablative etching of nitrocellulose membranes with CO 2 ( λ = 10.6 μ m), Nd : YAG ( λ = 1.06 μ m) and XeCl ( λ = 308 nm) lasers has been studied. From etch rate measurements the threshold fluence was estimated and the energy deposition at threshold fluence was calculated for the three wavelengths. The electron microscope examination of the infra-red laser ablated areas reveals a fairly clean etching under CO 2 laser irradiation, confirming that melting of the crater surroundings cannot be considered as a criterion for the thermal mechanism. It is proposed that the CO 2 laser, which also possesses some operational advantages, compared with excimer lasers, can be effectively used for the clean ablation of the nitrocellulose film dielectric.

Ablation of gelatin samples was performed by using a semiconductively preionized TEA CO2 laser, emitting pulses of the lower TEM mode, 100 ns duration, at a repetition rate of 2.4Hz. Ablation rate experiments were performed at a range of fluences from 2J cm−2 to 10J cm−2. Assuming that the absorption coefficient is much larger than the scattering coefficient, experimental data were explained by simple models of ablation. The ablation depth per pulse and the specific absorption depth were calculated from the experimental data.

In this work, ablation experiments of ex vivo porcine cornea tissue were conducted with two solid state lasers (an Er:YAG laser and the 4th harmonic of an Nd:YAG laser, both in the ns pulse width range) emitting in mid infrared and ultraviolet part of the spectrum respectively, at moderate laser fluences. The cornea epithelium of each porcine eye was manually removed before the ablation. Histology analysis of the specimens was performed, in order to examine the microscopic appearance of the ablated craters and the existence of any thermal or mechanical damage caused by the midinfrared and the UV laser irradiation. For a detailed and complete examination of the morphology of the laser ablated corneal tissue, the surface roughness was investigated by scanning electron microscopy.

Biophotonics techniques are applied to several fields in medicine and biology. The laser based techniques, such as the laser induced fluorescence (LIF) spectroscopy and the optical coherence tomography (OCT), are of particular importance in dermatology, where the laser radiation could be directly applied to the tissue target (e.g. skin). In addition, OCT resolves architectural tissue properties that might be useful as tumour discrimination parameters for skin as well as for ocular non-invasive visualization. Skin and ocular tissues are complex multilayered and inhomogeneous organs with spatially varying optical properties. This fact complicates the quantitative analysis of the fluorescence and/or light scattering spectra, even from the same tissue sample. To overcome this problem, mathematical simulation is applied for the investigation of the human tissue optical properties, in the visible/infrared range of the spectrum, resulting in a better discrimination of several tissue pathologies. In this work, we present i) a general view on biophotonics applications in diagnosis of human diseases, ii) some specific results on laser spectroscopy techniques, as LIF measurements, applied in arterial and skin pathologies and iii) some experimental and theoretical results on ocular OCT measurements. Regarding the LIF spectroscopy, we examined the autofluorescence properties of several human skin samples, excised from humans undergoing biopsy examination. A nitrogen laser was used as an excitation source, emitting at 337 nm (ultraviolet excitation). Histopathology examination of the samples was also performed, after the laser spectroscopy measurements and the results from the spectroscopic and medical analysis were compared, to differentiate malignancies, e.g. basal cell carcinoma tissue (BCC), from normal skin tissue. Regarding the OCT technique, we correlated human data, obtained from patients undergoing OCT examination, with Monte Carlo simulated cornea and retina tissues for diagnosis of ocular diseases.

Ablation rates measurements with free-running Er:YAG laser (λ=2.94 μm) were performed in hydrophilic acrylic intraocular lenses. We studied the role of water in the laser ablation mechanisms by using hydrophilic lenses with different concentrations of H20 and D20. A mathematical model simulated the experimental results.© (2007) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In recent years, lasers for optical trapping and micromanipulation of microscopic particles or cells and subcellular structures, both in vivo and in vitro, have gained remarkable interest in biomedical research and applications. On the other hand, a highly focused pulsed laser allows ablation and microdissection of biological material with high spatial resolution. In 1989 the microbeam field and the optical trapping field were merged by the first combination of laser microbeams and optical tweezers. Several laser sources are employed for the combination of a laser scalpel with an optical trapping device, under microscopic control. For example a pulsed laser microbeam that emits in the ultraviolet or the visible range of the electromagnetic spectrum can be used to form submicrometer cuts in biological material or to ablate parts specific cells. However, although the principles and the mechanisms of pulsed laser ablation have been well described for macroscopic interventions, the microbeam operation under microscopic guidance necessitates further investigation. In this work, we present the research and development efforts towards a pulsed UV microbeam laser system, the design and realization efforts towards a visible laser trapping system and the first results obtained on yeast cells by the combined system. The nitrogen laser microbeam setup, with special UV mirrors, lenses and a microscope in which ablation and the He-Ne optical tweezers are combined, performs the microsurgery and micromanipulation. This Uv laser based setup provides good spatial resolution for microdissection. The beam quality delivered by the laser is of great importance in microscopy controlled ablating operations and therefore was extensively studied.

Mid-IR lasers are already used successfully in numerous surgical operations. The Er:YAG and the HF laser, are the main laser sources emitting in the 3.0 μm range of the spectrum, and as this wavelength coincides with the peak of the water and other main soft and hard tissue components absorption curves, it is clear that these lasers would be very useful in numerous medical fields as dentistry, dermatology, angioplasty, ophthalmology etc. Recently, the development of flexible, low loss, able to deliver high power and safe to enter the human body waveguides and fibers for pulsed mid-infrared laser radiation initiated the efforts of the extension of laser surgery in the area of the minimally invasive endoscopy. The laser-induced fluorescence (LIF) is proposed for diagnosis in several pathologies, as in arterial atherosclerosis, in malignancy or for early dental caries detection. LIF is also investigated as a suitable method for monitoring the on line laser surgery interventions.

Conventional solid state laser pumping cavities has been used, after proper modification, in order to achieve efficient laser action by Cr:LiSAF crystals. The crystal samples were placed in the laser head, properly supported for efficient pumping to achieve satisfactory laser action. It has been proved that for a successful result a strong flash pumping source and a low output coupling is needed to help the low overall gain of the small Cr:LiSAF samples.

Hard dental tissue laser applications, such as preventive treatment, laser diagnosis of caries, laser etching of enamel, laser decay removal and cavity preparation, and more recently use of the laser light to enlarge the root canal during the endodontic therapy, have been investigated for in vitro and in vivo applications. Post-ablative surface characteristics, e.g. degree of charring, cracks and other surface deformation, can be evaluated using scanning electron microscopy. The experimental data are discussed in relevance with the laser beam characteristics, e.g. pulse duration, beam profile, and the beam delivery systems employed. Techniques based on the laser illumination of the dental tissues and the subsequent evaluation of the scattered fluorescent light will be a valuable tool in early diagnosis of tooth diseases, as carious dentin or enamel. The laser induced autofluorescence signal of healthy dentin is much stronger than that of the carious dentin. However, a better understanding of the transmission patterns of laser light in teeth, for both diagnosis and therapy is needed, before the laser procedures can be used in a clinical environment.

Transmission measurements of Q-switched Er:YAG laser radiation, through cyclic olefin polymer-coated silver hollow glass waveguides, were performed under straight and bent conditions and the beam quality at the output of the waveguide was studied.

The autofluorescence spectra of hard dental tissues, both in normal and pathological areas were investigated in this study. The measurements were performed both on the intact hard tissues of the examined teeth, such as enamel, dentine, cementum, and root canal, and on the tissues pathologically affected by caries (superficial, intermediate, and deep). Various laser wavelengths (337 nm, 488 nm, and 514 nm) were used to irradiate the dental surfaces and a computer-controlled spectrograph captured the fluorescent spectra. The emission signals were stored, measured, analyzed and quantified in terms of wavelength distribution and the relative photon intensity. Results indicated that the fluorescent spectra from healthy enamel, dentine, and cementum were almost identical in form, depending on the excitation wavelength. The intact and affected hard tissues were greatly different in the integral fluorescent intensity. Healthy areas were found to produce the most pronounced fluorescent intensity, whereas the carious regions produced the weaker fluorescent intensity. Independently of the laser excitation wavelength, dentin regions were found to produce the most pronounced fluorescent intensity than any other dental component. The fluorescence signal of carious affected dental structure revealed a reed shifted spectral curve, more pronounced after 488 nm excitation. There was a pronounced red shift for deep caries (crown -- root caries), after ultraviolet laser excitation. Excitation with visible wavelengths did not produce such differences between intact and cervical, deep carious affected tissue. Using a monochromatic light source without any light output at the wavelengths of fluorescence, e.g. a laser with the appropriate filters, the difference in fluorescence between intact and carious enamel was generally easy to observe. Finally, we found that the blue line of an argon ion laser is preferable for superficial caries detection, while the ultraviolet emitting nitrogen laser induces better discrimination in deep caries diagnosis.

Potassium 4S1/2 - 6S1/2 two-photon excitation initiates the emission of several internally generated photons. For the first time two emission lines one close and one below the potassium 4P3/2 level are reported. Radiation emitted below the 4P3/2 - 4S1/2 level is due to a Parametric Four Wave Mixing (PFWM) process initiated by the internally generated radiation from 5P3/2 - 4S1/2 level. The line emitted close to the 4P3/2 level is produced by a two-step Four Wave Mixing (FWM) process. Direct one photon driving of 4S3/2 - 4P3/2 transition produces similar to HEP radiation.

In this paper we present the basic features of the laser remote sensing (lidar) system located at the National Technical University of Athens (NTUA), Greece. This compact and mobile lidar is in full operation since late 1999. This paper includes basic features of the lidar technique (technical description, temporal and spatial resolution, range etc.), a brief presentation of the instrumentation used and an outline of the algorithms applied to retrieve useful information from the backscattered lidar signals. We also present some examples of aerosol profiling measurements over Athens, which include monitoring of clouds and suspended aerosols (i.e. during Saharan dust and photochemical air pollution events), as well as the evolution of the Planetary Boundary Layer (PBL) over the Greater Athens Area (GAA).

A pulsed Er:YAG laser and a preionised pulsed HF laser were used for the evaluation of the transmission properties of fluoride glass fibers as well as a cyclic olefin polymer-coated silver (COP/Ag) hollow glass and a silica hollow glass waveguide. Both lasers provided an output of 100 mJ/pulse, with a repetition rate of 1Hz at 3 μm wavelength. The pulse duration of the two lasers was 200 ns for the HF and 80μs for the Er:YAG. The evaluation of the fiber and waveguide properties include both straight and bend loss characteristics.

Laser beam deflection is a useful tool for studying the dynamics of the pulsed laser ablation mechanism, and has the advantage of being used as an in situ laser damage monitoring technique for both bulk and thin film polymeric and biological tissue samples. This work employs the photothermal deflection technique to study possible photo-acoustic phenomena during the excimer laser ablation of biocompatible polytetrafluoroethylene (PTFE) and to examine the crater surface quality by video microscopy.Although photo-acoustic phenomena are detected in the laser fluence threshold region, ablation is mainly the result of the photothermal process.

HF chemical lasers are of great interest as high power radiation sources in the 2.5 to 3.5μm range. Among their recent applications, requiring simple, compact, high power lasers, producing short pulses at high repetition rates are certain types of delicate laser surgery. A novel HF chemical laser design is described which fulfils all the requirements of delicate surgery. The performance characteristics of it are given and its advantages over the better known CO2 lasers as far as laser and tissue interaction, beam handling, delivery system and safety are analysed. These novel HF lasers, operating on SF6, C3H8 and He are operating with 12% efficiencies, specific energy extractions up to 36J/L and repetition rates up to 100Hz. To the best of our knowledge these figures compare very favourably with any corresponding figures reported update in the literature.

Intense laser operation is reported by a novel design of TEA laser heads employing double discharge and semiconductive preionisers-electrodes. Their performance, beam profile and electrical characteristics are presented and are compared to the characteristics of semiconductor or spark array preionised laser heads. These novel laser heads of minimum complexity are capable of producing N 2 laser pulses up to 12mJ of energy and efficiencies up to 0.11%, or CA 2 laser pulses up to 800 mJ of energy and efficiencies up to 5.6%, at pulse repetition rates up to 100 Hz. To the best of our knowledge, these figures compare favorably with any published figures, obtained from lasers of similar size.

A high current sliding discharge has been used to pump directly a N 2 :He mixture at an overall atmospheric pressure and produce laser output at 0.3371 μm and 0.3577 μm. In addition to that the sliding discharge has been used, to the best of our knowledge for the first time, to pump directly Ar and Xe and produce laser action at 1.79 μm, 1.27 μm and 0.912 μm from Ar:He mixtures and at 1.73 μm and 0.98 μm from Xe:He:Ar mixtures. The performance parameters of these lasers are given and among them their charging voltage, pressure and SF 6 addition dependence.

In this work optical tweezers with elliptical beam profiles have been developed in order to examine the effect of optical force on fresh red blood cells (RBC) in isotonic, hypertonic and hypotonic buffer solutions. Considering that the optical force depends essentially on the cell surface and the cytoplasmic refractive index, it is obvious that biochemical modifications associated with different states of the cell will influence its behaviour in the optical trap. Line optical tweezers were used to manipulate simultaneously more than one red blood cell.After we have been manipulated a RBC with an elliptical laser beam profile in an isotonic or hypertonic buffer, we noticed that it rotates by itself when gets trapped by optical tweezers and undergoes folding. Further shape deformations can be observed attributed to the competition between alignment and rotational torque which are transferred by laser light to the cell. In hypotonic buffer RBCs become spherical and do not rotate or fold since the resultant force due to rays emerging from diametrically opposite points of the cell leads to zero torque. Manipulation of fresh red blood cells in isotonic solution by line optical tweezers leads to folding and elongation of trapped RBCs. Membrane elasticity properties such as bending modulus can be estimated by measuring RBC’s folding time in function with laser power.

The plasma cathode design concept is applied to an Ar laser for the first time. The sliding discharge is used as a plasma cathode for the main laser discharge. The laser operates at atmospheric pressure with a gas mixture of Ar/He/SF6. Results concerning the dependence of the laser performance on the gas mixture flow rates and charging voltage are presented. The temporal behavior of the laser output is also presented. Output energies as high as 2 mJ, efficiency and specific energy extraction values up to 1.3×10−2% and 0.02 J/l respectively, at atmospheric pressure, are obtained. The spectroscopic examination of the output shows that lasing at 1.79 and 1.27 μm is obtained with approximately equal line intensities.