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The photoelastic dispersion coefficient represents the relationship between stress and the differences in refractive indices in a birefringent material. However, determining the coefficient using photoelasticity is challenging, as it is difficult to determine the refractive indices within photoelastic samples that are under tension. Here we present, for the first time, to our knowledge, the use of polarized digital holography to investigate the wavelength dependence of the dispersion coefficient in a photoelastic material. A digital method is proposed to analyze and correlate the differences in mean external stress with differences in mean phase. The results confirm the wavelength dependence of the dispersion coefficient, with an accuracy improvement of 25% compared to other photoelasticity methods.

We study the light–matter coupling by Raman scattering in colloidal suspensions composed by core–shell TiO2@Silica (Rutile@Silica) nanoparticles suspended in ethanol and water solutions. Strong enhancement of the Raman signal per particle is observed as [TiO2@Silica] is increased above a threshold, being stronger in ethanol suspensions. Moreover, above this [TiO2@Silica] threshold, the optical transmittance of the ethanol suspension starts to be considerably lower than in water, despite scattering strength being higher in water. These results are attributed to localization of light induced by strong correlation in the scatterers’ position as a consequence of the long-range Coulomb interaction between the TiO2@Silica nanoparticles. Light diffraction in TiO2@Silica suspensions (water and ethanol) shows strong correlation in the scatterers’ position (structure seemingly cubic), being stronger in ethanol than in water (longer-range Coulomb interaction). As a result, we demonstrate in these colloidal suspensions for the first time, to our knowledge, strongly enhanced light–matter coupling through correlation-induced localization with klT much higher than unity and in an ordered colloidal-photonic structure. This strong enhancement of light–matter coupling by localization of light opens an avenue for manufacturing powerful sensing tools.

We demonstrate two highly efficient Nd:YLiF4 lasers, achieving the highest efficiencies for Nd:YLF side-pumped at 800 nm.

Three laser resonators are demonstrated emitting at 1053 nm and pumped at 797 nm by volume Bragg grating-equipped diodes, achieving the highest reported efficiencies for Nd:YLF in a four-level system, to the best of our knowledge. A peak output power of 880 W is achieved by pumping the crystal with a diode stack of 1.4 kW of peak pump power.

When considering dynamically stable resonators, ring lasers are good choices because they have a stability interval that is twice as large as that of linear resonators and sensitivity to misalignment decreasing with pump power; however, the literature does not provide easy design guidelines. A ring resonator utilizing Nd:YAG side pumped by diodes allowed single-frequency operation. The output single-frequency laser had good output characteristics; however, the overall length of the resonator did not allow for building a compact device with low misalignment sensitivity and larger spacing between longitudinal modes which could improve single-frequency performance. Based on previously developed equations, which allow for ease of design of a ring dynamically stable resonator, we discuss how to build an equivalent ring resonator, aiming to building a shorter resonator with the same stability zone parameters. The study of the symmetric resonator containing a pair of lenses allowed us to find the conditions to build the shortest possible resonator.

A Nd:YAG rod single-frequency ring laser based on side-pumped commercial modules is presented. Thermally induced birefringence compensation was applied in a dynamically stable resonator providing 55.6 W of continuous, linearly polarized, TEM00 output. The particular case of a symmetric ring resonator containing one or two focusing rods and a pair of curved mirrors was analyzed and a design technique is presented, allowing for easy, continuous shaping of the stability limits by changing only the distances in the resonator.

Made available in DSpace on 2019-10-06T15:41:27Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-07-25 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Optical waveguide amplifiers have seen a growing interest in the last years due to their applications in telecommunication. This paper reports a notable increase of the relative gain of Yb3+/Er3+ codoped Bi2O3–GeO2 waveguides by introducing disorder in the form of silicon nanostructure as scattering centers. A photoluminescence enhancement of about 10 times for the 520 nm and 1530 nm emission bands is observed in the waveguides when the silicon nanostructures are introduced. Increase of the Yb3+/Er3+ effective absorption, due to the scattering provided by the silicon nanostructures, and decrease of [Bi+], caused by the introduction of silicon, are proposed as likely causes for the luminescence and gain enhancement. The pedestal waveguides were fabricated by RF-sputtering followed by optical lithography and reactive ion etching. RF-sputtering of silicon together with Yb/Er and Bi2O3–GeO2 glass, followed by heat treatment, produced Yb3+/Er3+ codoped Bi2O3–GeO2 waveguides with silicon nanostructures of size 25–30 nm. The resulting relative gain reached 5.5 dB/cm at 1542 nm representing an enhancement of 50% with respect to waveguides without silicon nanostructures. This strategy of introducing appropriate disorder may open an avenue for designing and manufacture of novel photonic devices in this emerging field of integrated optics. Centro de Lasers e Aplicações Instituto de Pesquisas Energéticas e Nucleares CNEN-IPEN/SP, Av. Prof. Lineu Prestes 2242 Escola Politécnica Universidade de São Paulo Faculdade de Tecnologia de São Paulo CEETEPS/UNESP Faculdade de Tecnologia de São Paulo CEETEPS/UNESP FAPESP: 2013/26113-6 CNPq: 465.763/2014 FAPESP: PV-2017/05854-9

Random lasers hold the premise for cheap coherent light sources that can be miniaturized and molded into any shape and used for speckle-free imaging in biology, remote sensing, display technology, encrypting, cancer detection and distributed amplification. However, they require improvements specifically in terms of efficiency and low emission threshold. This work details for the first time a strategy for increasing the efficiency of a random laser that consists in using smaller particles, trapped between large particles to serve as absorption and gain centers whereas the large particles control mainly the light diffusion into the sample. A record slope efficiency of more than 50% was achieved using yttrium vanadate particles with mean particle size of 54 μm by optimizing the distribution of the polydispersed particles. In addition, random lasing with very low emission threshold (0.24 mJ/cm2) is also reported in a strongly disordered optical medium that is in the transition regime to Anderson localization composed by a colloidal suspension of core–shell TiO2@Silica nanoparticles in ethanol solution of rhodamine 6G. A promising method called fraction of absorbed pump power allowed us to infer the emission threshold for localized modes (peaks mode). The classical super-fluorescence band (ASE) of the random laser was measured separately by collecting the emission at the back of the samples, showing a linear dependence with pumping fluence without gain depletion. The intensity of peaks during Anderson transition is approximately equal within a broad frequency range, indicating suppression of the interaction between the peak modes. The random lasers have been characterized by measurements of backscattering cone, absorption and reflection measurement, transport mean free path, average photon path length and fill fractions.

Here we compare the efficiency and beam parameters of different single-bounce Nd:YLF 4 resonators. A total of five cavities were made by changing both, the curved mirror and the output coupler of the resonator. The best configuration resulted in a cavity that generated a record optical-to-optical efficiency of 63.3% and 66.4% of slope efficiency, with a peak output power of 64.5 W for a pumping power of 101.8 W at 797 nm.

We report the fabrication and passive characterization of Nd3+ doped TeO 2 -ZnO glass with a new configuration of double waveguides, written with fs laser operating at 800 nm, delivering 30 fs pulses at 10kHz repetition rate. The two written lines that form the double waveguide are formed by several overlapping lines. Results of output mode profile, beam quality factor M2 and refractive index change are presented as well as the parameters used for laser writing. Writing speed of 0.5 mm/s and pulse energy of 15 μJ demonstrated to be adequate parameters for writing. Refractive index changes of An = 1×10−5 and An = 1×10-4 were found at 632 nm for double waveguides written with 4 and 8 overlapping lines, respectively. The mode image results at the output of the waveguides showed a confined beam in agreement with multi transverse order mode. Beam quality factor results were the following: M y = 24±3 and Mx= 14±3 at 632 nm. The glasses are produced with the melt quenching technique and the preliminary results demonstrated that they are promising materials for the fabrication of passive and active components for photonic applications.

We report on a Nd:YLF4 laser diode-side-pumped at 863 nm, resulting in 75% slope efficiency and 13.8 W of CW output power.

Low heat generation can be obtained when pumping Nd:YLF at wavelengths of 872 nm and 880 nm and emitting at the three-level transition of 908 nm. These transitions show very low quantum defect with efficiencies of 0.96 and 0.97, respectively. However, the low average absorption cross-section at these wavelengths makes efficient absorption even for longitudinal pump setups difficult. Using a beam-shaped pump diode instead of a fiber-coupled diode bar may be an effective means of increasing absorption because it can provide for π-polarized radiation which shows higher absorption cross section. In this work, a Nd:YLF was pumped at 872 nm by a diode bar using beam-shaping. Results were compared to pumping at 872 and 880 nm with non-polarized fiber-coupled diodes. Stimulated Raman scattering was also obtained with a KGW crystal generating first Stokes emissions at 990 nm and 976 nm.

Diode-side pump Nd:YAG rod modules are widely available, reliable and commercially very attractive for building continuous-wave solid-state lasers in the 10-1000 W range. Newer technologies such as fiber or thin disk lasers are generally much more expensive but have the benefit of better beam quality and higher output powers if necessary. By using well-known techniques for designing dynamically stable resonators (DSRs), lasers with high extraction efficiency and high beam quality (fundamental mode, TEM00) can be obtained also with diode side-pumped modules. However, a successful project for a dynamic stable laser depends critically on the correct choice of the fundamental mode diameter within the rod. DSR design rules are based on the beam waist, w3, at the rod principal planes by considering the rod as a thin thermal lens, which differs significantly from real resonators. Here we give guidelines and criteria on how to establish the correct diameter in each case. Using off-the-shelf 75 W Nd:YAG modules it was possible to obtain linearly polarized TEM00-mode output of 30 W with M2=1.08 from a single module, M2=1.2 and 76.5 W of output power using two modules and 100.5 W of polarized, continuous output with M2=1.8. A single-frequency ring laser was also built, using two modules, generating 51.6 W of fundamental wave single-frequency output.

An Nd:YLF/KGW intracavity Raman laser in DBMC (double-beam-mode-controlling) configuration has been investigated in this work. The fundamental wavelength laser was generated using a Nd:YLF crystal pumped in DBMC configuration generating an emission wavelength of 1053 nm in σ-polarization. A VBG (volume-Bragg-grating) equipped diode emitting at 797 nm was used as pump source. The KGW crystal has two strong Raman lines, 768 cm-1 and 901 cm-1, generating two Raman wavelengths at 1147 nm and 1163 nm, respectively. The DBMC technique allows to produce TEM00 stable output in a side-pumped configuration with no requirement to introduce any additional mode selection technique, thus achieving high efficiency for fundamental TEM00 operation. The high power density of the fundamental laser combined with intracavity Stokes conversion produces an efficient Raman laser. Allying both techniques, the Nd:YLF in DBMC configuration and the intracavity Raman generation, it was possible to generate an output power at 1163 nm of 3.2 W corresponding to a diode-to-Raman conversion efficiency of 8% with slope efficiency of 8.8 %. For the emission at 1147 nm, 3.5 W of output power was achieved with a diode-to-Raman conversion efficiency of 11% and slope efficiency of 9%. The beam quality was M2 =1.9 and 1.1 in the horizontal and vertical direction, respectively. This is, to our knowledge, the first report of a side-pumped Nd:YLF/KGW intracavity Raman laser in DBMC configuration.

Polarized Digital Holography (PHD) is a fast and efficient tool for analyzing mechanical effects in materials. Especially when the task requires non-invasive techniques that do not damage the material in study, the use of PHD has great perspectives. The most common methods of digital reconstruction use the convolution theory to discretize the Huygens- Fresnel integral. When external stresses are applied to photoelastic materials, the relationship between these stresses and phase differences observed by polarization holography is an intrinsic characteristic of the material called the photoelastic dispersion coefficient. In photoelasticity, this coefficient depends on the wavelength. By using PHD the authors show in the present paper that the photoelastic dispersion coefficient also depends on the wavelength in Holography. A Mach- Zehnder interferometer, modified with the inclusion of linear polarizers, was built to verify this effect in a sample of photoelastic material. In this set-up, two coherent light sources with different wavelengths were used. For the analysis, a digital method was created that correlated the mean stresses differences on the photoelastic material sample and the mean phases differences at each distinct wavelength.

Nanoparticles represent a promising platform for diagnostics and therapy of human diseases. For biomedical applications, these nanoparticles are usually coated with photosensitizers regularly activated in a spectral window of 530–700 nm. The emissions at 530 nm (green) and 660 nm (red) are of particular interest for imaging and photodynamic therapy, respectively. This work presents the Mg2SiO4:Er3+ system, produced by reverse strike co-precipitation, with up to 10% dopant and no secondary phase formation. These nanoparticles when excited at 985 nm show upconversion emission with peaks around 530 and 660 nm, although excitation at 808 nm leads to only a single emission peak at around 530 nm. The direct upconversion of this biomaterial without a co-dopant, and its tunability by the excitation source, renders Mg2SiO4:Er3+ nanoparticles a promising system for biomedical applications.

We report the fabrication and characterization of double line waveguides directly written in tellurite and germanate glasses using a femtosecond laser delivering 30 μJ, 80 fs pulses at 4 kHz repetition rate. The double line waveguides produced presented internal losses inferior to 2.0 dB/cm. The output mode profile and the M 2 measurements indicate multimodal guiding behavior. A better beam quality for the GeO 2 – PbO waveguide was observed when compared with TeO 2 – ZnO glass. Raman spectroscopy of the waveguides showed structural modification of the glassy network and indicates that a negative refractive index modification occurs at the focus of the laser beam, therefore allowing for light guiding in between two closely spaced laser written lines. The refractive index change at 632 nm is around 10 −4 , and the structural changes in the laser focal region of the writing, evaluated by Raman spectroscopy, corroborated our findings that these materials are potential candidates for optical waveguides and passive components. To the best of our knowledge, the two double line configuration demonstrated in the present work was not reported before for germanate or tellurite glasses.

Made available in DSpace on 2018-11-30T03:15:34Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-01-01 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Silica aerogel is a lightweight material, well known for its good mechanical and thermal characteristics, but its optical properties have received less attention, because it is weakly scattering. Here we present for the first time the lasing properties and their complex dynamics of silica aerogel doped with R6G. It is shown that the Q factors of the lasing modes determine the operation of the laser, being either resonant or ASE-lasing. For resonant lasing, the number of resonators is easily varied and the number of modes in a single resonator and their emission frequency can be dynamically adjusted, making this a truly versatile photonics material. CNEN IPEN SP, Ctr Lasers & Aplicacoes, Ave Prof Lineu Prestes 2242, BR-05508000 Sao Paulo, Brazil Univ Estadual Paulista, Inst Quim Araraquara, Rua Prof Francisco Degni 55, BR-14800900 Sao Paulo, Brazil Univ Estadual Paulista, Inst Quim Araraquara, Rua Prof Francisco Degni 55, BR-14800900 Sao Paulo, Brazil CNPq: 402241 2012_6 CNPq: 307989 2013-5 FAPESP: 18162-4 2012 FAPESP: PV-2017/05854-9

Random lasers have the potential for cheap and coherent light sources which, in the particular case of colloidal suspensions, are completely flexible and can take on any desired shape. Here, we studied random lasing in correlated colloidal systems composed by TiO2@Silica nanoparticles suspended in ethanol solutions of Rhodamine 6G. TiO2 particles with two different silica layers (thicknesses of 40 nm and 70 nm) were prepared. The Random laser performance improves when the silica shell is thicker (70 nm), which was attributed to a stronger localization of light (higher density of localized states) induced by stronger correlation in the scatterers' (TiO2@Silica) position as a consequence of a stronger and longer-range Coulomb interaction between the scatterers. Light diffraction patterns in both TiO2@Silica suspensions showed a stronger correlation in the scatterers’ position, being stronger when the silica shell is thicker.

Dynamically stable operation with joined stability zones of a linearly polarized resonator is shown for a laser containing two diode side-pumped Nd:YAG rods. The unpolarized resonator generated 115 W of output. When polarized by a Brewster plate, it reached 100.5 W of output power at a beam quality M2 < 2. Best measured beam quality was of 1.1 and 1.3 in the x and y directions respectively, with 76 W of 95% polarized output. The output power achieved is, to our knowledge, the highest reported for continuous polarized, fundamental-mode lasers using standard side-pumped Nd:YAG modules.

Anderson localization of light and random lasing in this critical regime is an open research frontier, which besides being a basic research topic could also lead to important applications. This article investigates the random laser action at the localization transition in a strongly disordered scattering medium composed of a colloidal suspension of core-shell nanoparticles (TiO@Silica) in ethanol solution of Rhodamine 6G. The classical superfluorescence band of the random laser was measured separately by collecting the emission at the back of the samples, showing a linear dependence with pumping fluence without gain depletion. However, frontal collection showed saturation of the absorption and emission. Narrow peaks of approximately equal intensity are observed on top of the classical superfluorescence band, indicating suppression of the interaction between the peaks modes. The linewidth of these peaks is lower than that of the passive modes of the scattering medium. A method called fraction of absorbed pumping allowed us to infer that this peak's mode (localized modes) is confined to a shallow region near the input-pumping border., We gratefully acknowledge financial support from FACEPE, FAPESP, FAPESQ, and CNPq (Brazil). E.J.-V. acknowledges FACEPE (grant 0116-1.06/13, APQ-0071-1.06/14) and FAPESQ. I.F.S. thanks the CAPES (Brazil) for the fellowships of masters. N.U.W. acknowledges CNPq (grants 402241 2012_6 and 307989 2013-5) and FAPESP (grant 18162-4 2012). C.L. acknowledges Spanish MINECO (grant MAT2015-68075-R (SIFE)) and the Comunidad de Madrid (grant S2013/MIT-2740 (PHAMA_2.0)).

A single-frequency ring laser using two standard commercial diode-pumped Nd:YAG modules is demonstrated. Employing a dynamically stable resonator design, multi-longitudinal mode operation at 1064 nm with 53 W of output power was obtained. When inserting a LBO crystal in the resonator, 1.8 W of single-sided, single-frequency output at 532 nm was achieved. The measured linewidth was 3.6 MHz, close to the resolution limit of the scanning etalon used to measure the longitudinal mode structure.

In this work we review the recent advances in pedestal waveguide amplifier fabrication. The improvement of conventional photolithography and plasma etching methods brings advantages that benefit light guiding and reduce propagation losses, mainly in the 3rd telecommunication windows (λ~1550 nm). Yb3+/Er3+ codoped Bi2O3-GeO2 thin films, with and without Si nanostructures, are obtained by RF Magnetron sputtering deposition and are used as core layer of 500 nm height in the pedestal waveguides. Choosing an appropriate amount of these silicon nanostructures inside the rare-earth waveguides we achieve pump light scattering and at the same time very little scattering at the signal wavelength. The overall effect is again enhancement of 50% thus opening possibilities for potential applications in integrated optics.

A random rhodamine laser system is produced on board of a femtosecond laser machined microfluidic system. When pumped by a nanosecond pulsed laser beam at 532 nm, laser emission at 610 nm is observed together with the linewidth narrowing typical of random lasers. The system can be easily integrated as an optofluidic component into microfluidic circuits for assessment of optical parameters on board of the lab-on-chip.

A diode side-pumped Nd:YLiF4 crystal for fundamental wavelength generation and intracavity Stokes conversion in KGW are employed to obtained 6.1W maximum output power, 11.9% slope efficiency and 11.8% diode-to-yellow conversion efficiency at 573 nm.

This Joint Issue of Optics Express and Optical Materials Express features 15 articles written by authors who participated in the international online conference Advanced Solid State Lasers held 13–16 October, 2020. This review provides a summary of the conference and these articles from the conference which sample the spectrum of solid state laser theory and experiment, from materials research to sources and from design innovation to applications.

Wavelengths in the yellow-orange range are of significant interest for retinal photocoagulation and are especially important in the case of diabetic retinopathy, which can cause blindness and affects 3.3% of all working-age adults. This work presents a highly-efficient, compact, and cost-efficient side-pumped, intracavity Raman configuration to achieve this objective. A side-pumped Nd:YLF/KGW/LBO frequency-doubled Raman laser producing 11.7 W of output power at 1147 nm with 21% of slope efficiency and 6 W of output power at 573.5 nm with 12% slope efficiency is demonstrated.

We report on a Yb3+:KGW self-Raman laser operating at 1096 nm. A 100 µm fiber-coupled diode end-pumped configuration is used to generate a fundamental emission wavelength that strongly depends on internal resonator losses. Stokes emission at 1096 nm is achieved with a slope efficiency of 42 ± 8%, an optical conversion efficiency of more than 32% and a maximum output power of 4.5 W for quasi-continuous operation (1 ms pulses). The explored Stokes conversion of 89 cm−1 shows excellent laser characteristics, indicating that this still little explored Stokes shift could pave the way to continuous-wave Raman frequency-comb lasers.

We report the production of active double waveguides in Er/Yb doped GeO2-PbO glasses, by direct femtosecond laser writing. The glasses were produced using the melt-quenching technique and the active waveguides were written using 30 fs laser pulses, at 800 nm, with writing speed of 0.06 mm/s and pulse energy of 32 μJ. The photo-induced negative refractive index change was of −7.4 × 10−3. The Er/Yb doped sample showed a relative gain (signal enhancement of 7.5 dB/cm, for 105 mW of 980 nm pump power. The relative gain compensates both, the propagation losses and the absorption losses, and a positive maximum internal gain of 4.6 dB/cm can be obtained at the signal wavelength of 1550 nm. The results obtained in present work demonstrate that Er/Yb glasses are promising materials for the fabrication of integrated amplifiers, lossless components and lasers based on germanate glasses.

Objectives This clinical trial aimed to evaluate dental color stabilization after different bleaching techniques. Methods Four dental bleaching techniques were tested in 60 healthy volunteers aged from 25 to 35 years randomly assigned to four groups. Group 1 (G1): conventional in-office bleaching using 35% hydrogen peroxide. Group 2 (G2): in-office application of 3% hydrogen peroxide followed by in-office bleaching using 35% hydrogen peroxide. Group 3 (G3): in-office application of 3% hydrogen peroxide and activation with a light emitting diode (LED) lamp. Group 4 (G4): at-home bleaching using 10% carbamide peroxide. The color of canines and incisors was scored using a digital spectrophotometer to analyze lightness, chroma and hue. Results All groups resulted in shade change. Lightness increased in all groups with no statistical difference among groups 60 days after finishing the treatment regardless of the technique used (p > 0.05). Differences were found in a short-term evaluation between some groups (p 0.05). Analyzing canines, G4 showed higher chroma compared to G1 (p Conclusions All techniques improved lightness. The addition of 3% hydrogen peroxide to conventional in-office whitening only increased appointment time, but no further benefits were noticed. Clinical relevance This study is important to help clinicians deciding which is the most suitable dental bleaching for each patient in the current high aesthetic demanding world.

Non-contact evaluation of object deformation is of great importance in several industrial and scientific processes. In this work the demonstrate that low-coherence digital speckle pattern interferometry can be employed for pressure measurement by the analysis of a 0.4-mm thickness, 55-mm diameter circular aluminum membrane submitted to a pressure differential ranging from 0 to 90 kPa. The membrane deformation was measured with a tunable red diode laser emitting simultaneously two wavelengths. The resulting speckle image of the membrane appeared covered with interference fringes which correspond to the contour lines of the studied surface. By means of conventional fringe pattern evaluation methods like 4-stepping and unwrapping methods the membrane deformation was determined. The experimental results were compared with the ones obtained by a numerical algorithm.

In recent years, there has been a dramatic progress in the photonics field of disordered media, ranging from applications in solar collectors, photocatalyzers, random lasing, and other novel photonic devices, to investigations into fundamental topics, such as localization of light and other phenomena involving photon interactions. Anderson localization of light is an open researcher frontier, which has greatly attracted the attention of researchers in the past few decades. In this work, we study the transport of light in a strongly disordered optical medium composed by core-shell nanoparticles (TiO 2 cSilica) suspended in ethanol solution. We demonstrate the crossover from a diffusive transport to a localization transition regime as TiO 2 cSilica nanoparticle concentration is increased. A striking phenomenon of enhanced absorption, mainly near the input border, arises at the localization transition, from which an increase of refractive index was inferred. An increase of the density of localized states and absorption near the input border is reported when the incidence angle is increased. The specular reflection, measured for the photons that enter the sample, is considerably lower than the effective internal reflection undergone by the coherently backscattered photons in the exact opposite direction, indicating a nonreciprocal propagation of light (parity-symmetry breaking). A theoretical simulation, performed through random-matrix theory, agrees satisfactorily with the experimental results, showing the generality of this approach to address transport phenomena.

Scattering media are of great current interest, due to their potential applications in photovoltaic cells, efficient photocatalyzers, random lasers and novel optical functional devices. Here, we have introduced a core–shell scattering medium for random lasing composed by core-shell nanoparticles (TiO2cSilica) suspended in an ethanol solution of Rhodamine 6G. Higher efficiency, lower laser threshold and long photobleaching lifetime were demonstrated in random laser. A promising method called fraction of absorbed pumping (FAP) has been introduced, which opens a new avenue to characterize and study scattering media. In this article, we also investigate the random laser action at the critical regime of localization by increasing considerably the concentration of TiO2cSilica nanoparticles. Narrow peaks arising in the random laser emission spectrum are observed. The classical superfluorescence band of the random laser was measured separately by collecting the emission at the back of the samples, showing a linear dependence with pumping fluence without gain depletion. However, frontal collection showed the saturation of emission and absorption. The emission spectrum of the peak mode (localized modes) shows approximately equal intensity, indicating suppression of the interaction between the peaks modes. The linewidth of these peaks is lower than that of the passive modes of the scattering medium, which was attributed to an anomalous nonlinear increase of the refractive index by localization.

The authors report the fabrication and characterization of passive waveguides in GeO2–PbO and TeO2–ZnO glasses written with a femtosecond laser delivering pulses with 3μJ, 30μJ and 80fs at 4kHz repetition rate. Permanent refractive index change at the focus of the laser beam was obtained and waveguides were formed by two closely spaced laser written lines, where the light guiding occurs between them. The refractive index change at 632 nm is around 10-4 . The value of the propagation losses was around 2.0 dB/cm. The output mode profiles indicate multimodal guiding behavior. Raman measurements show structural modification of the glassy network. The results show that these materials are potential candidates for passive waveguides applications as low-loss optical components.

Wavelengths in the yellow-orange range are of significant interest due to their application potential in the medical and biomedical areas, as well as for applications in laser displays and in remote sensing. These wavelengths can be obtained by frequency-doubling or sum-frequency generation of lasers with near-IR emission like VCSELS, fiber lasers, and OPOs. However, all these alternatives have several limitations that justify the development of alternative methods. As a possible solution for these limitations, a configuration of an intracavity converted Raman laser may be developed to obtain two wavelengths, 1163 nm, and 1147 nm, with high efficiency and good beam quality. This paper presents a configuration of a side-pumped intracavity converted Raman laser to achieve these objectives. A Nd:YLiF4 crystal was used as fundamental wavelength gain crystal. The side-pumped configuration guarantees practicability and cost reduction while allowing good efficiency and fundamental mode laser beam. The intracavity conversion configuration allows high fundamental wavelength power at the Stokes crystal in order to facilitate the obtention of the Stokes wavelengths and enables optimization of its efficiency. As a result an output power at 1163 nm of 3.8 W in the multimode regime was obtained, corresponding to a pump to Stokes efficiency of 9.6%. The TEM00 diode to Stokes efficiency was 7%. For the emission at 1147 nm, 1.5W of output power with a diode to Stokes efficiency of 3.7% was achieved. The side-pumped Nd:YLF/KGW intracavity Raman laser configuration is reported for the first time, to our knowledge.

The backscattered light originated when machining with femtosecond laser pulses can be used to accurately measure the processed surface position through an interferometer, as recently demonstrated by our group, in a setup that uses the same laser beam for ablation and inspection. The present work explores the characteristics of the laser light reflected by the target and its interaction with the resulting plasma to better understand its propagation physics and to improve the dynamic focusing system. The origin of this returning radiation was studied and has been traced, mainly, from the peripheral area of the focal spot (doughnut-like). By means of a Mach-Zehnder setup, the interferometric pattern was measured and analyzed aiming to access the influences of the plasma on the laser beam properties, and therefore on the retrieved information. Finally, the wavefront of the laser that creates and propagates through the plasma was characterized using a Shack-Hartmann sensor.

Nd:YLiF4 is the gain material of choice whenever outstanding beam quality or a birefringent gain material is necessary such as in certain applications for terahertz radiation or dual-frequency mode-locking. However, for high power CW applications the material is hampered by a low thermal fracture threshold. This problem can be mitigated by special 2D pump set-ups or by keeping the quantum defect to a minimum. Direct pumping into the upper laser level of Nd:YLiF4 is usually performed at 880 nm. For quasi-three level laser emission at 908 nm, direct pumping at this wavelength provides a high quantum defect of 0.97, which allows for very high CW pump powers. Although the direct pumping transition to the upper laser state at 872 nm has a slightly smaller quantum defect of 0.96, its pump absorption cross section along the c-axis is 50% higher than at 880 nm, leading to a higher absorption efficiency. In this work we explore, for the first time to our knowledge, 908 nm lasing under 872 nm diode pumping and compare the results with 880 nm pumping for quasicw and cw operation. By inserting a KGW crystal in the cavity, Raman lines at 990 nm and 972 nm were obtained for the first time from a directly pumped 908 nm Nd:YLF fundamental laser for both quasi-cw and cw conditions.

A simple, reliable, linearly polarized laser source with very high beam quality is demonstrated using standard diode-side-pumped Nd:YAG modules. The laser produced 30 W of output power with beam quality factor M2

This paper reports for, the first time, the influence of silicon nanocrystals on the photoluminescence and optical gain of Yb 3p /Er 3p codoped Bi 2 O 3 −GeO 2 waveguides for amplification at 1542 nm. Pedestal waveguides were fabricated by RF- sputtering followed by optical lithography and reactive ion etching. RF-sputtering followed by heat treatment produced silicon nanocrystals with average size of 8 nm and resulted in a photoluminescence enhancement of about 10 times for the 520 nm and 1530 nm emission bands. The resulting internal gain was 5.5 dB/cm at 1542 nm, which represents and enhancement of ∼50p, demonstrating potential for applications in integrated optics.