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Colorizing metals using micrometer and nanometer scale surface modifications has been vastly investigated and presents many advantages for applications across scientific and technological fields. By tuning the surface chemical composition or controlling its morphology, it is possible to produce a wide range of chromatic effects. Ultrafast laser processing presents here an interesting asset, as it allows to simultaneously provide chemical and morphological modifications at the micro‐scale in a single step. In this article, the composite colorization of copper surfaces with mW‐class average power deep ultraviolet (DUV) femtosecond laser pulses is demonstrated. The advantages of this setup are twofold: first, thanks to the increased absorption of copper in the DUV, the technique allows scaling down the requirement for laser power. Second, under ultrafast short‐wavelength illumination molecular oxygen bond‐breaks occur, enhancing the oxidation rate of the copper. The technique allows for highly controllable and efficient copper oxidation with the irradiation parameters. Taking these two effects into account, the generation of a wide spectrum of colors—from dark blue to shiny red—is demonstrated, and the role of the surface oxidation rate, the laser fluence, and laser scanning strategies in the colorization of copper surfaces employing DUV lasers is discussed. [ABSTRACT FROM AUTHOR]

The formation of micro-scale tracks in the bulk of porous glass samples using femtosecond laser pulses was investigated, which is of interest for laser writing of active optical waveguides. It was ascertained that the impregnation of nanoporous glass with a bismuth nitrate solution effects the appearance of an orange luminescence band on excitation at 488 nm, which is intensified in the formed tracks. It is demonstrated that increasing the laser pulse energy to 200 nJ makes it possible to increase the phase contrast for tracks written in nanoporous glass containing bismuth, compared to tracks recorded in additive-free nanoporous glass. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate a SESAM mode-locked Tm:CaYLuAlO4 (a-cut) laser in the 2-μm spectral range. A birefringent filter (BF) is employed to shift the emission wavelength above 2 μm to support the stable mode locking through avoiding the structured water vapor absorption. Pulses as short as 288 fs are generated with a central wavelength of 2037 nm and an average power of 166 mW at a repetition rate of ~ 77.6 MHz. Moreover, wavelength tunable femtosecond laser with a tuning range from 2031.8 to 2081.1 nm is realized simply by rotating the birefringent filter around its surface normal. This work experimentally shows that birefringent filter is a simple and low-cost way to support the stable mode locking of Tm-bulk femtosecond lasers with an emission peak in the water vapor absorption region. [ABSTRACT FROM AUTHOR]

The beam self-cleaning phenomenon is theoretically predicted by the two-dimensional nonlinear Schrödinger equation, which describes self-focusing, and is observed in the case of femtosecond laser filamentation in the collimated regime of propagation. However, the impact of external focusing on the self-cleaning has not been investigated so far. In this paper we systematically study this impact in a wide range of focusing conditions. We show that the energy range, in which self-cleaning can be observed, shrinks monotonically with the numerical aperture growth at some point vanishing at all. [ABSTRACT FROM AUTHOR]

This paper presents results of femtosecond laser micromachining of a transparent glass-ceramic in the Li2O–Al2O3–SiO2 system with a near-zero linear thermal expansion coefficient in the thermal and athermal regimes. Electron microscopy and electron diffraction data confirm complete amorphization of nanocrystals of β-eucryptite-like solid solutions under the effect of laser pulses. Using quantitative phase microscopy, we have evaluated refractive index changes in individual laser-written tracks. In the athermal regime at a pulse repetition rate of 10 kHz, complete glass-ceramic amorphization leads to a decrease in the refractive index of the material (Δn = −0.0035) in the laser treatment region, which opens up the possibility of using direct laser writing of channel waveguides in a thermally stable glass-ceramic matrix. [ABSTRACT FROM AUTHOR]

We investigate the evolution mechanisms of the laser-induced periodic surface structures (LIPSS) and quasi-periodic grooves that are formed on the surface of monocrystalline silicon (mono-Si) when exposed to femtosecond laser radiation of different pulse duration, state of polarization, and fluence. The conditions required for producing LIPSS-free complex micro-ridge patterns are elaborated. The LIPSS evolution mechanism is explained in terms of scattering/interference-based phenomena. To establish the basis for our interpretation, single femtosecond pulses of different pulse durations are irradiated on mono-Si. The absence/appearance of LIPSS rudiments is explained in the context of spectral bandwidth and the associated effects on the intensity of the central wavelength. Shorter fs pulses of a wider bandwidth are employed to induce LIPSS-free micro-ridge patterns. It is demonstrated that the resultant micro-ridge patterns depend on the laser fluence distribution and can be manipulated through laser polarization. The curved morphology of LIPSS rudiments and the evolution mechanism of low- and high-spatial frequency LIPSS, i.e., LSFL and HSFL, are discussed. Finally, it is demonstrated that the consolidated quasi-periodic grooves result from HSFL welding together groups of LSFL. Although our findings are based on fs laser interaction with mono-Si, the results can also be applied to many other materials. [ABSTRACT FROM AUTHOR]

Multiphoton photopolymerisation (MPP), also known as 3D nanoprinting, was studied using a wavelength-tunable femtosecond laser. The possibility of using any colour of the spectrum from 500 to 1200 nm with a fixed pulse width of 100 fs revealed an interplay of photophysical mechanisms more delicate than just two-photon photopolymerisation. An effective order of absorption, i.e. the X-photon absorption, as well as optimal exposure conditions were assessed for photosensitised and pure SZ2080TM pre-polymer. The tunability of wavelength greatly influenced the dynamic fabrication window (DFW), optimised conditions resulting in a 10-fold increase. Furthermore, a non-trivial energy deposition by X-photon absorption was noted with an onset of a strong lateral size increase at longer wavelengths and can be understood as due to reaching epsilon-near-zero conditions. Such a control over the voxel aspect ratio and, consequently, the photopolymerised volume, may boost 3D nanoprinting efficiency. Overall, the results reveal wavelength being an important degree of freedom to tailor the MPP process and, if optimised, benefiting broad applications in areas of micro-optics, nanophotonic devices, metamaterials and tissue engineering. [ABSTRACT FROM AUTHOR]

THz radiation through a novel scheme based on a three-pulse configuration in two-dimensional ordinary and extraordinary modes was investigated. The electromagnetic radiation driven by the linear and nonlinear current density created by the laser-induced plasma mechanism has been evaluated. The numerical findings of the present study show that the electric field of THz radiation is significantly improved compared to the two-color scheme if the third harmonic is included. The asymmetric three-color femtosecond laser fields can be used to control the polarization state, radiation power, and the directivity of the THz radiation. With adjustable time delays between pulses, the polarization controllability of THz radiation from plasma, based on experimental conditions, can be achieved. With this scheme, not only tuning to circularly polarized THz radiation is feasible, but also linear or elliptical polarization can be realized by adjusting time delays. The effects of different laser profiles and wavelengths on ionization rate are considered. Variation of the electric field of the generated THz waves for both ordinary and extraordinary modes of photocurrent mechanism is examined numerically for various spatial laser profiles. The study indicates that a laser pulse profile can be used to control THz radiation. [ABSTRACT FROM AUTHOR]

Femtosecond laser machining of materials has transformed into a mature high‐precision technology, giving access to a wide range of applications. Yet, for a complete exploitation of its full potential, a detailed knowledge of the complex laser–matter interaction processes is required. For the case of the application‐relevant material steel, a complete study of the electron dynamics and material transformation upon single laser pulse irradiation (800 nm, 120 fs) is reported. Detailed analysis of the obtained time‐ and fluence‐dependent reflectivity map reveals that ultrafast electron heating during the pulse is directly followed by energy transfer to the lattice within a few picoseconds, reaching fluence‐dependent peak temperatures from below melting threshold to above the boiling point. Moreover, an innovative approach to obtain the ultrafast‐evolving 3D structure of a femtosecond laser excited material is reported, unraveling the dynamics of complex processes as melting, ablation, and solidification. Combined with modeling, the evolving optical properties, multilayer structure, and expansion velocities can be precisely determined. The information obtained from this study will contribute to further increase the achievable precision and wealth of structures that can be produced by designing efficient pulsed energy deposition schemes for selective re‐excitation of the material. [ABSTRACT FROM AUTHOR]

This work demonstrates for the first time the formation of nanogratings inside Barium Gallo-Germanate (BGG) glasses using femtosecond laser direct writing. These heavy oxide glasses, with a characterized transparency window up to 6 μ m, along with the polarization sensitive birefringent nanostructures induced by femtosecond laser, offer an excellent platform for the development of mid-Infrared photonic applications. The fabricated glasses, containing both rare earth elements (Gd, Y) and transition metals (Zn, Ta), are directly compared to amorphous GeO 2 and commercial alumino-germanate (Corning-9754) glasses commonly used in this field. The nanogratings processing window in each glass was investigated by varying laser parameters (pulse duration, energy, repetition rate), and electron microscopy imaging directly evidenced the porous nanostructures. Among the results, a strong form birefringence in 8% ZnO containing BGG glass, e.g., up to −0.029 ± 0.001, was reported. Finally, birefringent embedded Fresnel GRIN plates were directly written in a BGG glass, to demonstrate the functionalization potential of these materials. [ABSTRACT FROM AUTHOR]

Explicit visualization of different components of surface plasmon polaritons (SPPs) propagating at dielectric/metal interfaces is crucial in offering chances for the detailed design and control of the functionalities of plasmonic nanodevices in the future. Here, we reported independent imaging of the vertical and horizontal components of SPPs launched from a rectangular trench in the gold film by a 400-nm laser-assisted near-infrared (NIR) femtosecond laser time-resolved photoemission electron microscopy (TR-PEEM). The experiments demonstrate that distinct imaging of different components of SPPs field can be easily achieved by introducing the 400-nm laser. It can circumvent the risk of sample damage and information loss of excited SPPs field that is generally confronted in the usual NIR laser TR-PEEM scheme. The underlying mechanism for realizing distinct imaging of different components of the SPPs field with two-color PEEM is revealed via measuring the double logarithmic dependence of photoemission yield with the 800-nm and 400-nm pulse powers of different polarizations. Moreover, it is found that the PEEM image quality of the vertical and horizontal components of the SPPs field is nearly independent of the 400-nm pulse polarization. These results pave a way for SPPs-based applications and offer a possible solution for drawing a spaceâ€"time field of SPPs in three dimensions. [ABSTRACT FROM AUTHOR]

Over the last decade, lasers have been gradually employed for Si wafer dicing to replace blade dicing. Laser dicing has the potential to replace blade dicing as the future generation ultrathin wafer singulation method as it enables higher cutting speed, lower damage, and smaller kerf width but various technical challenges still remain to be resolved. In this article, laser ablation and dicing of Si wafers are reviewed in terms of the physics of laser-material interaction based on nanosecond, picosecond, and femtosecond pulse durations. The effects of various laser settings, dicing process parameters, and material factors on ablation rate, ablation precision and quality, and die fracture strength are discussed in detail. With the increasing usage of Cu stabilization layer on the backside of ultrathin Si wafers, we also review laser-material interaction in Cu and elaborate on recent findings on the effects of laser dicing through Si and Cu simultaneously on the microstructural and fracture strength properties of the die. Various approaches to improve the ablation rate, ablation quality, and die fracture strength are discussed. • Laser dicing of thin Si wafers is gaining more importance in the semiconductor industry because of its cost-effectiveness compared to conventional blade dicing. • Understanding laser ablation mechanisms remains a huge challenge because of the complexity of the processes taking place, the variety of species involved, and the range of length and time scales covered. • Many challenges remain for laser dicing of Si wafers primarily in three critical areas, i.e., ablation rate, ablation precision and quality, and die fracture strength. • Optimization of the ablation rate, ablation quality, and die fracture strength will require thorough consideration of all the influencing laser and process parameters in order to meet the requirements of the end product applications. [ABSTRACT FROM AUTHOR]

We have proposed a scheme to increase the ultra-intense femtosecond laser absorption efficiency by using carbon aerogel targets. Particle-in-cell simulations show that, compared to a homogeneous target of the same density, the carbon aerogel target can significantly enhance the laser absorption efficiency, and the maximum laser absorption efficiency can reach 88%. Such high absorption efficiency can be attributed to the porous structure and larger surface area of carbon aerogel than ordinary materials, which allows the laser to enter more of the target and interact more fully with the particles inside rather than being reflected off the surface. By studying the interaction between the laser and the carbon aerogel targets, we found that both the nanoparticle diameter and porosity have great effects on the laser absorption efficiency, which is enhanced significantly as the nanoparticle diameter and porosity increase. Such carbon aerogel targets should have significant applications in the fields of laser generation of x rays and high energy density physics. [ABSTRACT FROM AUTHOR]

Laser direct writing is a widely employed technique for 3D, contactless, and fast functionalization of dielectrics. Its success mainly originates from the utilization of ultrashort laser pulses, offering an incomparable degree of control on the produced material modifications. However, challenges remain for devising an equivalent technique in crystalline silicon which is the backbone material of the semiconductor industry. The physical mechanisms inhibiting sufficient energy deposition inside silicon with femtosecond laser pulses are reviewed in this article as well as the strategies established so far for bypassing these limitations. These solutions consisting of employing longer pulses (in the picosecond and nanosecond regime), femtosecond‐pulse trains, and surface‐seeded bulk modifications have allowed addressing numerous applications. [ABSTRACT FROM AUTHOR]

With the development of femtosecond (fs) laser technology, an fs laser pulse with 10s of Joule, even 100s of Joule energy is available and the focused laser intensity can be expected to induce the pure Coulomb explosion of the cluster with a much larger average radius than before. Meanwhile, the production of gas cluster with an average radius of upto 10s of nanometer has been possible. In this case, it is necessary to reinvestigate the feasibility of 109 n/shot neutron yield for the practical application in the intense fs laser-driven nuclear fusion. In this work, the neutron yield from the explosions of the D2 clusters of 6–20 nm average radius at the 0.5–100 J pulse energy and the CD4 clusters was investigated theoretically. It is found that the optimum neutron yield of 109 n/shot can be obtained at the laser energy and the cluster radius currently available. However, a clustered-gas jet with a large cross-section is demanded to match the proper plasma diameter. [ABSTRACT FROM AUTHOR]

The reconnection rate in relativistic magnetic reconnection driven by two relativistic intense femtosecond laser pulses is investigated using three-dimensional particle-in-cell (PIC) simulation. As the drive is enhanced, the current sheet is narrowed, and the reconnection rate is weakened. A new theoretical model is given to explain the rate observed in the PIC simulation. In addition, multi-scale reconnection is studied by setting a different ion mass in the simulation code. For , the current sheet is only at the electron scale, and only electron outflow jets are observed, which are super ion Alfvénic and close to the electron's Alfvénic speed. The lengths of the electron outflow jets reach 100–200 times the length of the electron gyroradius and beyond the ion gyroradius. However, when , more ions are coupled to electrons during the laser and plasma interaction, there are also electron outflow jets and no ion outflow jets in the current sheet, and the electron outflow jets are embedded in a wider ion-scale current layer. [ABSTRACT FROM AUTHOR]

In this paper, a non-reciprocal writing effect is proposed on the silicon by a femtosecond laser with tailor of temporal chirp. The induced structures which belong to the written lines with two opposite scans show obvious difference in the ablated regions. The grating compressor of a laser system is controlled to change the temporal chirp so as to flip the direction of the pulse front tilt, which results in 2 types of induced structures exchanging between two opposite scans. We assume, during the laser scans along the pulse front tilt, there may have a snowplow effect on the excited free electrons, leading to an asymmetrical electrical field distribution around the focal area. This process could further boost an ionization efficiency in the next pulse irradiation as well as make the induced structures grow faster. Current result possibly offers a new route to control the density of free electrons excited when femtosecond laser interacts with silicon wafer. [ABSTRACT FROM AUTHOR]

SwissFEL is a compact, high-brilliance, soft and hard X-ray free electron laser (FEL) facility that started user operation in 2019. The facility is composed of two parallel beam lines seeded by a common linear accelerator (LINAC), and a two-bunch photo-injector. For the injector, an innovative dual-photocathode laser scheme has been developed based on state-of-the-art ytterbium femtosecond laser systems. In this paper, we describe the performance of the SwissFEL photocathode drive lasers (PCDLs), the pulse-shaping capabilities as well as the versatility of the systems, which allow many different modes of operation of SwissFEL. The full control over the SwissFEL electron bunch properties via the unique architecture of the PCDLs will enable in the future the advent of more-advanced FEL modes; these modes include, but are not restricted to, the generation of single or trains of sub-femtosecond FEL pulses, multi-color FEL and finally, the generation of fully coherent X-ray pulses via laser-based seeding. [ABSTRACT FROM AUTHOR]

Reconfigurable micromachines that are highly conscious of changing environments have significant potential for use in biomedical applications, such as minimally invasive surgery, cell manipulation, and tissue engineering. Current nanofabrication approaches with sophisticated designs appear to enhance the controllability of shape transformations, such as bending, folding, and twisting, while minimizing the response time. However, the construction of three-dimensional (3D) structures at a small scale with a high shape-morphing freedom poses challenges because of the lack of applicable materials and effective fabrication techniques. Here, we develop an advanced four-dimensional microprinting strategy for constructing 3D-to-3D shape-morphing micromachines in a single-material-single-step mode. Using direct laser writing, heterogeneous stimulus-responsive hydrogels can be distributed spatially into arbitrary 3D shapes with sub-micrometer features. The material crosslinking densities, stiffnesses, and swelling/shrinking degrees can be modulated by programming the exposure dosage of femtosecond laser pulses and characterized to predict the shape-morphing behaviors via finite-element methods. With our proposed approach, complex 3D reconfigurable compound micromachines with mechanical advantages, which exhibit an excellent deformation-amplifying effectiveness, can be constructed to achieve a rapid, precise, and reversible 3D-to-3D shape transformation in response to multiple external stimuli, and they emerge as promising smart and multifunctional micromachine candidates for various engineering applications. [ABSTRACT FROM AUTHOR]

Femtosecond laser irradiation in Au@Ag, Ag@Au core@shell, and Au–Ag Janus-like nanoparticles are investigated using molecular dynamics simulations. Our results show that the morphology of Au@Ag core–shell and Au–Ag Janus-like nanoparticles tend to form hollow-like nanostructures due to the ultrafast energy transfer and the subsequent cooling process. In contrast, our results also shows that Ag@Au nanoparticles do not form a hollow structure due to the high diffusion of Ag atoms and the limited expansion of the Au shell. Besides, successive laser impacts on the Au–Ag Janus-like nanoparticle produce a structure that alternates from hollow to a solid nanoparticle and, at the same time, promotes atomic diffusion, favoring the alloying process of the Ag and Au atoms. In addition, the evolution of the crystalline structure is studied, observing a saturation of the planar defects due to the impossibility of forming a new crystalline phase. The energy variation between the initial and final step, it is not influenced by the presence of the hollow, however it is dominated by the increase of planar defects. [Display omitted] • A novel method to produce alloy nanoparticles is proposed. • Ultrafast laser produce hollow and Janus AuAg nanoparticles. • Successive laser irradiation controls size and shape of the samples. [ABSTRACT FROM AUTHOR]

The morphology of microchannels machined by multiple ultrafast laser pulses with 500 fs and 8 ps durations on fused silica plate is predicted by a two-step model with experimental validation in present work. A spike structure at crater boundary with different scales in 500 fs and 8 ps pulse ablation is found in the numerical investigation, which could be attributed to diffraction and attenuation of light intensity in both cases. To analyze the evolution of crater morphology and damaged area with an increasing number of pulses, the distribution of light intensity, lattice temperature, and self-trapped excitons density during certain pulses are studied. The results showed that 500 fs pulses lead to smoother crater boundary, smaller heat affected zone, and larger electrical damage area with respect to 8 ps pulses. [ABSTRACT FROM AUTHOR]

[Display omitted] • For near-threshold double-pulse femtosecond laser processing of titanium, the maximum ablation area occurred at the double-pulse pulse separation of 1 ps. • Through the pump–probe microscopy technique, the surface melted into the liquid metal film within 10 ps. The liquid metal showed lower reflectivity of the second sub-pulse, which facilitate more energy deposition of the surface layer and the enhancement of the ablation area. • Combined observation and experimental and theoretical analysis, the thermal and mechanical damage both affected the ablation result. The maximum ablation enhancement is obtained at a suitable time separation (about 1 ps), due to the opposite effect of these two damage mechanisms. Near-threshold femtosecond laser surface treatment of titanium produces functional nanostructures, which has received much attention in applications and scientific researches. However, researches on the mechanism of near-threshold temporally-shaped femtosecond laser ablation of titanium are scarce, because the difficulty of investigating the modification mechanism of surface properties by sub-pulses below the ablation threshold. In this study, the double-pulse femtosecond laser ablation with various pulse separation was investigated. We found that the maximum ablation area appeared around 1 ps pulse separation at different fluences, and the ablation enhancement weakened with the increase of the fluence. The ultrafast pump–probe microscopy technique and ultrafast thermoelasticity model were used to investigate the mechanism. The result of pump–probe microscopy technique indicated that the enhancement of the area was caused by the decrease of transient reflectivity in the early stages which facilitated the subsequent sub-pulse energy absorption. The theoretical results indicate that the maximum ablation enhancement occurred at 1 ps, which is due to the combination of thermal and mechanical effects. The maximum of long axis diameter of periodic structure also appeared at 1 ps in multi-point processing. These findings have significant implications for the modulation of titanium surface nanostructures and providing theoretical support for processing. [ABSTRACT FROM AUTHOR]

The peculiarity and higher suitability of NbMoTaW over its composed elemental metals for femtosecond laser induced LIPSS/particle-aggregate UV-to-MIR ultrabroadband absorber are firstly revealed. The performance of ultrabroadband absorbers is adjustable by changing the density of NbMoTaW particle aggregates on laser induced periodic surface structures (LIPSS) with increasing repetition rate from 0.5 to 1 MHz and laser power from 1 to 12 W till a whole coverage at 12 W and 1 MHz, under which condition only lower-performance microstripes consisting of particle-aggregate and LIPSS (on Mo, Ta, and W) or macropore/LIPSS micro/nanostructures (on Nb) are achievable on elemental metals. NbMoTaW-LIPSS decorated by a few particle aggregates is more suitable than LIPSS itself to be used as selective solar absorber, indicating the capacity of deposited particle aggregates to modulate absorbance selectivity. It is deduced that NbMoTaW-RHEA should possess a lower melting temperature than W and a high electron-phonon coupling constant, facilitating nano-structuring/nano-synthesis. [Display omitted] [ABSTRACT FROM AUTHOR]

• First demonstration of NIR femtosecond Pr solid-state laser of any type. • Double-sided symmetric dispersion arrangement by introducing a triple set of GTIs. • The Pr:YLF crystal is pumped by a single blue laser-diode. • 915-nm ultrafast pulse of 451 fs width at a repetition rate of 85.5 MHz. • This Pr laser has an average output power of 257 mW and a pulse energy of 3 nJ. Femtosecond pulse generation from diode-pumped praseodymium (Pr) lasers in the near-infrared has been a long pursuit for the optics community. Utilizing the Pr:LiYF 4 crystal in a novel dispersion arrangement scheme that includes a set of triple Gires-Tournois interferometer mirrors, mode-locked ultrashort pulses as short as 451 fs at 915 nm have been achieved when the crystal is directly pumped by a blue laser-diode. The pulse energy is 3 nJ and peak power is 7.2 kW at the repetition rate of 85.5 MHz. This is the first demonstration of diode-pumped Pr lasers arriving the femtosecond regime. [ABSTRACT FROM AUTHOR]

This work aim to achieving laser nano-textured Si structures by means of an ultra-fast ultra-violet femtosecond (fs) laser texturing technique. The evidences of the impact of the duration of irradiation of the femtosecond laser pulses on Silicon (Si) have been investigated experimentally. A Ti:Sapphire laser at 800 nm (130 fs pulse duration with 1 kHz rate of repetition) has been employed to create nano-textured surfaces in an n-type (111) Si wafer of 0.015 Ω.cm resistivity and 508 ± 5 μm thickness. The average sizes of diameters were estimated to be in the 25−45 nm. From PL measurements of Si nanostructures, size dependent shifts in the direction of the blue spectral region have been emphasized. A highly symmetrical band shape was recognized from the samples' Raman spectra after the irradiation, the phonon frequency (phonon peak shift) shifted below 520 cm−1. The surface nanostructured Si showed lower reflectance values compared with bulk Si (un-irradiated). The observed enhancement of the fabricated Si nanostructures broad spectral response, which is in the range between the visible to the near infrared (NIR) 400−1150 nm, was attributed to increasing light absorption within sub-nanostructures. Thus, the proposed technique could be a promising approach to enhance the performance of Si-based photo-detector. [ABSTRACT FROM AUTHOR]

We report on the laser performance of diode-pumped continuous-wave Nd:CaLaGa 3 O 7 laser after registering the polarized absorption and emission spectra, for the first time to our knowledge. A maximum output power of 1.45 W is reached at 1061.7 nm and 1067.8 nm with a slope efficiency of about 27.7% with respect to the absorbed power. Wavelength tuning is also realized with a range of about 22 nm using an intracavity un-doped YAG etalon. The broadband Nd3+-doped crystal could be very promising for ultrashort pulse laser generation in femtosecond time duration through mode locking technology. • Absorption and emission spectra of Nd:CaLaGa 3 O 7 crystal are measured. • Diode-pumped Nd:CaLaGa 3 O 7 laser is reported, for the first time to our knowledge. • Wavelength tuning of the Nd:CaLaGa 3 O 7 laser with a range of about 22 nm is reported. • This work indicates Nd:CaLaGa 3 O 7 is very promising for femtosecond laser generation. [ABSTRACT FROM AUTHOR]

• The laser beam creates colored voxels inside a transparent medium. • Voxel colors are determined by their luminescence and light scattering spectra. • Media with excitonic mechanism of defect creation are applicable for color recording. • Recording technology includes three stages of laser irradiation and heat treatment. The problem of creating three different types of spatially selective voxels by laser radiation in the volume of an transparent optical medium was solved. Each of the created voxels provides one base color: red, green, or blue. Red and green voxels are microvolumes inside a crystal in which femtosecond laser pulses create luminescence centers that emit, respectively, in the red and green regions of the spectrum when illuminated with blue radiation that excites luminescence. Voxels responsible for the blue glow are microvolumes in which light scattering centers are created by femtosecond pulses. These voxels do not contain any luminescence centers; they scatter blue radiation, which excites the luminescence of red and green voxels. To solve the problem of creating spatially separated voxels of all three types in the volume of an optical carrier, we studied the temperature dependences of the spectra, the output, and the decay time constants of the luminescence of quantum systems created by femtosecond laser radiation. These dependences were studied during heating and cooling. The change in the voxel size of the three basic colors from the energy and the number of femtosecond pulses of a titanium-sapphire laser was studied. Irradiation regimes were found in which only luminescence centers are formed in voxels and scattering centers are not formed. On the basis of the results, a three-stage technology of laser irradiation and heat treatment of optical media was proposed and experimentally tested. This technology allows for creation of three-dimensional, full-color images, visualized under blue light. [ABSTRACT FROM AUTHOR]

• Experimental study on the performances of laser in the net normal or net anomalous dispersion region. • Stable mode-locked pulses with a duration of 94 fs centered at 1050 nm. • The pulse energy is 59 nJ and the peak power is 0.56 MW. We investigated the performance of diode pumped mode-locked Yb:CGA laser operating in the net normal or net anomalous dispersion region. With 26 W pump power, stable femtosecond laser pulses with average power of 4.5 W are obtained, yielding a pump power slope efficiency of 17%. Operating at 80.5 MHz repetition rate, the laser delivers as short as 93 fs pulse duration with average output power of 4.5 W, corresponding to a pulse energy of 56 nJ and a peak power of 0.59 MW. The oscillator exhibits a passive rms power stability of ~0.38% rms over 5 h in high beam quality. [ABSTRACT FROM AUTHOR]

• A femtosecond laser was focused into a microfluidic chip and applied to particle manipulation. • Intensity and directionality of the impulse were optimized by a pocket structure fabricated in the channel of the chip. • The femtosecond laser-induced impulse realized on-chip particle manipulation within 10 μs. We report a high-speed manipulation method to control flow direction of micro-particles in microfluidic chip activated by a femtosecond (fs) laser impulse. When the femtosecond laser pulse is focused in the channel, a micro-explosion is induced and generates an impulsive force at the laser focal point. In this method, the impulsive force initiated inside a micro-structure in the channel is applied to manipulate micro-particles flowing in the channel. Specifically, a directional force loading to the particle is realized by an additive pocket structure fabricated in the channel. When the laser is focused at the entrance of the pocket fabricated perpendicular to the channel, we could enhance directionality and intensity of the impulsive force and realize an effective particle manipulation compared with the chip without assistance of the pocket structure. The enhancement was apparently observed in a longer and wider pocket, especially whose entrance width is narrower than the pocket end width. The manipulation process occurs in less than 10 micro-seconds which is a potential high-speed manipulation method for single micro-particles. [ABSTRACT FROM AUTHOR]