Suitable labels are at the core of Luminescence and fluorescence imaging and sensing. One of the most exciting, yet also controversial, advances in label technology is the emerging development of quantum dots (QDs)--inorganic nanocrystals with unique optical and chemical properties but complicated surface chemistry--as in vitro and in vivo fluorophores. Here we compare and evaluate the differences in physicochemical properties of common fluorescent labels, focusing on traditional organic dyes and QDs. Our aim is to provide a better understanding of the advantages and limitations of both classes of chromophores, to facilitate label choice and to address future challenges in the rational design and manipulation of QD labels.

/pdf/quantum-dots-versus-organic-dyes-as-fluorescent-labels-50cbzj94q6.pdf

Quantum dots versus organic dyes as fluorescent labels

The rise time of intense radiation determines the maximum field strength atoms can be exposed to before their polarizability dramatically drops due to the detachment of an outer electron. Recent progress in ultrafast optics has allowed the generation of ultraintense light pulses comprising merely a few field oscillation cycles. The arising intensity gradient allows electrons to survive in their bound atomic state up to external field strengths many times higher than the binding Coulomb field and gives rise to ionization rates comparable to the light frequency, resulting in a significant extension of the frontiers of nonlinear optics and (nonrelativistic) high-field physics. Implications include the generation of coherent harmonic radiation up to kiloelectronvolt photon energies and control of the atomic dipole moment on a subfemtosecond $(1{\mathrm{f}\mathrm{s}=10}^{\mathrm{\ensuremath{-}}15}\mathrm{}\mathrm{s})$ time scale. This review presents the landmarks of the 30-odd-year evolution of ultrashort-pulse laser physics and technology culminating in the generation of intense few-cycle light pulses and discusses the impact of these pulses on high-field physics. Particular emphasis is placed on high-order harmonic emission and single subfemtosecond extreme ultraviolet/x-ray pulse generation. These as well as other strong-field processes are governed directly by the electric-field evolution, and hence their full control requires access to the (absolute) phase of the light carrier. We shall discuss routes to its determination and control, which will, for the first time, allow access to the electromagnetic fields in light waves and control of high-field interactions with never-before-achieved precision.

Intense few-cycle laser fields: Frontiers of nonlinear optics

We stabilized the carrier-envelope phase of the pulses emitted by a femtosecond mode-locked laser by using the powerful tools of frequency-domain laser stabilization. We confirmed control of the pulse-to-pulse carrier-envelope phase using temporal cross correlation. This phase stabilization locks the absolute frequencies emitted by the laser, which we used to perform absolute optical frequency measurements that were directly referenced to a stable microwave clock.

/pdf/carrier-envelope-phase-control-of-femtosecond-mode-locked-4lkf4vexna.pdf

Carrier-envelope phase control of femtosecond mode-locked lasers and direct optical frequency synthesis

We review the field of femtosecond pulse shaping, in which Fourier synthesis methods are used to generate nearly arbitrarily shaped ultrafast optical wave forms according to user specification. An emphasis is placed on programmable pulse shaping methods based on the use of spatial light modulators. After outlining the fundamental principles of pulse shaping, we then present a detailed discussion of pulse shaping using several different types of spatial light modulators. Finally, new research directions in pulse shaping, and applications of pulse shaping to optical communications, biomedical optical imaging, high power laser amplifiers, quantum control, and laser-electron beam interactions are reviewed.

Femtosecond pulse shaping using spatial light modulators

Ultrafast lasers, which generate optical pulses in the picosecond and femtosecond range, have progressed over the past decade from complicated and specialized laboratory systems to compact, reliable instruments. Semiconductor lasers for optical pumping and fast optical saturable absorbers, based on either semiconductor devices or the optical nonlinear Kerr effect, have dramatically improved these lasers and opened up new frontiers for applications with extremely short temporal resolution (much smaller than 10 fs), extremely high peak optical intensities (greater than 10 TW/cm2) and extremely fast pulse repetition rates (greater than 100 GHz).

Recent developments in compact ultrafast lasers

We report on dye fluorescence enhancement (10-fold) with high spatial confinement (100nm-deep, 1µm-wide) on a photonic crystal (PhC) through resonant excitation of photonic modes. These features make the PhC an excellent substrate for fluorescence microscopy.

Fluorescence microscopy on a 2D photonic crystal transparent in the visible

Drug-resistant epilepsy occurs in about 30% of epilepsy patients. It has been suggested that etiology or seizure type would increase the risk of pharmacoresistance. This study aims to compare the characteristics of patients with drug-sensitive epilepsy with patients with drug-resistant epilepsy to identify risk factors.A multicentric cohort study was conducted between 2019 and 2022. We included patients >18 years-old with epilepsy but excluded psychogenic non-epileptic seizures and less than 2 years of follow-up.We included 128 patients, of whom 46 had drug-resistance epilepsy, and 82 responding to medication. Both groups showed similar characteristics. Febrile seizures (OR: 7.25), focal epilepsy (OR: 2.4), focal seizures with loss of consciousness (OR: 2.36), structural etiology (OR: 2.2) and abnormal MRI (OR: 4.6) were significant risk factors for drug-resistance epilepsy.Following other studies, we observed that factors such as epilepsy type, seizure type, structural etiology, abnormal MRI, and febrile seizure increased the risk for drug-resistance epilepsy, in our population. 

Risk factors for drug-resistant epilepsy in adult patients.

In this work we compare two different detection schemes that are sensitive to the focus shift of a probe beam due to induced surface curvature. The technique on which both detection schemes are based is called ThERM (Thermal Expansion-Recovery Microscopy) and allows the retrieval of the thermal diffusivity at microscopic levels, hence mapping such magnitude over a sample surface. The induced thermal expansion defocuses the probe beam due to the surface deformation (curvature). The dependence of the defocusing with the pump modulation frequency yields the thermal diffusivity of the sample at the impinging location. The explored depth is controlled by the pump beam size. By scanning both beams, a complete map of the thermal diffusivity can be retrieved.

Thermal Expansion-Recovery Microscopy (ThERM) for microstructural characterization

In the silicon ribbon on a sacri cial template process silicon is deposited on both sides of a carbon ribbon, thus forming a Si/carbon/Si trilayer. The fast cooling of the ribbon in large temperature gradients generates stresses that are detrimental to both the electrical performance and the mechanical behaviour of the wafers. The assessment of the stresses is crucial for the setting-up of thermal treatments allowing for the stress relaxation of the wafers, prior to the cell fabrication. We present an analysis of the stress in the as-grown trilayer by a simulation of the thermomechanical behaviour of the cooling ribbon. Experimental measurements of the stress in as-grown and annealed trilayers are also presented. The results permit to establish the conditions for optimized growth and annealing.

/pdf/raman-study-of-multicrystalline-silicon-wafers-produced-by-1wu7u2v7ii.pdf

Oscar E. Martínez

Papers

Fluorescence microscopy on a 2D photonic crystal transparent in the visible

Risk factors for drug-resistant epilepsy in adult patients.

Thermal Expansion-Recovery Microscopy (ThERM) for microstructural characterization

Raman Study of Multicrystalline Silicon Wafers Produced by the RST Process

Comparison of Outdoor and Indoor PL and EL Images in Si Solar Cells and Panels for Defect Detection and Classification