We demonstrate that sample induced aberrations can be measured in a nonlinear microscope. This uses the fact that two-photon excited fluorescence naturally produces a localized point source inside the sample: the nonlinear guide-star (NL-GS). The wavefront emitted from the NL-GS can then be recorded using a Shack-Hartmann sensor. Compensation of the recorded sample aberrations is performed by the deformable mirror in a single-step. This technique is applied to fixed and in vivo biological samples, showing, in some cases, more than one order of magnitude improvement in the total collected signal intensity.
<b><i>Background:</i></b> Around 10% of newborn infants require assistance during transition after birth. Heart rate (HR) is the most important clinical indicator to evaluate the clinical status of a newborn. <b><i>Aim:</i></b> Our study aimed to review all established and novel methods to detect HR in babies giving special consideration to non-invasive techniques. <b><i>Methods:</i></b> We performed a systematic literature search on the following databases: MEDLINE, Embase, Cochrane Central Register of Controlled Trials (CENTRAL), and CINAHL. The inclusion criteria were studies on methods to detect HR in both term and preterm infants in comparison to one of the current gold standards: pulse oximetry (PO) or electrocardiography (ECG) published in the last 15 years. Two independent reviewers screened titles and abstracts for eligibility. Data extracted in an Excel table were analysed to produce a narrative review structured around the type of monitoring, identified obstacles in use, as well as methods to overcome these limitations. <b><i>Results:</i></b> The search revealed 649 studies after duplicates were removed. Full article analysis was performed on 26 studies of which 25 met the inclusion criteria. Well established methods such as auscultation and palpation, although rapid and easily available, have been shown to be inaccurate. ECG and PO were both more precise but the delay in obtaining a reliable HR signal from birth often exceeded 1–2 min. Novel sensors offered the advantages of minimally obtrusive technologies but have limitations mainly due to movement artefact, bad sensor coupling, intermittent measurement, and poor-quality recordings. <b><i>Conclusions:</i></b> The limitations of existing methods have a potential impact on short- and long-term morbidity and mortality outcomes. The development of a technological solution to determine HR accurately and quickly in babies at birth has immense implications for further research and can guide interventions, such as placental transfusion and resuscitation.
We present a portable ultrafast Semiconductor Disk Laser (SDL) (or vertical extended cavity surface emitting laser—VECSELs), to be used for nonlinear microscopy. The SDL is modelocked using a quantum-dot semiconductor saturable absorber mirror (SESAM), delivering an average output power of 287 mW, with 1.5 ps pulses at 500 MHz and a central wavelength of 965 nm. Specifically, despite the fact of having long pulses and high repetition rates, we demonstrate the potential of this laser for Two-Photon Excited Fluorescence (TPEF) imaging of in vivo Caenorhabditis elegans (C. elegans) expressing Green Fluorescent Protein (GFP) in a set of neuronal processes and cell bodies. Efficient TPEF imaging is achieved due to the fact that this wavelength matches the peak of the two-photon action cross section of this widely used fluorescent marker. The SDL extended versatility is shown by presenting Second Harmonic Generation images of pharynx, uterus, body wall muscles and its potential to be used to excite other different commercial dyes. Importantly this non-expensive, turn-key, compact laser system could be used as a platform to develop portable nonlinear bio-imaging devices.
Abstract. Live microscopy techniques ͑i.e., differential interference contrast, confocal microscopy, etc.͒ have enabled the understanding of the mechanisms involved in cells and tissue formation. In long-term studies, special care must be taken in order to avoid sample damage, restricting the applicability of the different microscopy techniques. We demonstrate the potential of using third-harmonic generation ͑THG͒ microscopy for morphogenesis/embryogenesis studies in living Caenorhabditis elegans ͑C. elegans͒. Moreover, we show that the THG signal is obtained in all the embryo development stages, showing different tissue/structure information. For this research, we employ a 1550-nm femtosecond fiber laser and demonstrate that the expected water absorption at this wavelength does not severely compromise sample viability. Additionally, this has the important advantage that the THG signal is emitted at visible wavelengths ͑516 nm͒. Therefore, standard collection optics and detectors operating near maximum efficiency enable an optimal signal reconstruction. All this, to the best of our knowledge, demonstrates for the first time the noninvasiveness and strong potential of this particular wavelength to be used for highresolution four-dimensional imaging of embryogenesis using unstained C. elegans in vivo samples. © 2010 Society of Photo-Optical Instrumentation Engineers.
Abstract:In this paper, we present the generation of high peak-power picosecond optical pulses in the 1.26 μm spectral band from a repetitionrate-tunable quantum-dot external-cavity passively mode-locked laser (QD-ECMLL), amplified by a tapered quantum-dot semiconductor optical amplifier (QD-SOA). The laser emission wavelength was controlled through a chirped volume Bragg grating which was used as an external cavity output coupler. An average power of 208.2 mW, pulse energy of 321 pJ, and peak power of 30.3 W were achieved. Preliminary nonlinear imaging investigations indicate that this system is promising as a high peak-power pulsed light source for nonlinear bio-imaging applications across the 1.0 μm -1.3 μm spectral range.
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