Strong-field physics with mid-IR fields

Strong-field physics is currently experiencing a shift towards the use of mid-IR driving wavelengths. This is because they permit conducting experiments unambiguously in the quasi-static regime and enable exploiting the effects related to ponderomotive scaling of electron recollisions. Initial measurements taken in the mid-IR immediately led to a deeper understanding of photo-ionization and allowed a discrimination amongst different theoretical models. Ponderomotive scaling of rescattering has enabled new avenues towards time resolved probing of molecular structure. Essential for this paradigm shift was the convergence of two experimental tools: 1) intense mid-IR sources that can create high energy photons and electrons while operating within the quasi-static regime, and 2) detection systems that can detect the generated high energy particles and image the entire momentum space of the interaction in full coincidence. Here we present a unique combination of these two essential ingredients, namely a 160\~kHz mid-IR source and a reaction microscope detection system, to present an experimental methodology that provides an unprecedented three-dimensional view of strong-field interactions. The system is capable of generating and detecting electron energies that span a six order of magnitude dynamic range. We demonstrate the versatility of the system by investigating electron recollisions, the core process that drives strong-field phenomena, at both low (meV) and high (hundreds of eV) energies. The low energy region is used to investigate recently discovered low-energy structures, while the high energy electrons are used to probe atomic structure via laser-induced electron diffraction. Moreover we present, for the first time, the correlated momentum distribution of electrons from non-sequential double-ionization driven by mid-IR pulses.Comment: 17 pages, 11 figure

Systems and Methods for Measuring Ultra-Short Light Pulses

Systems and methods for measuring a pulse length (.tau..sub.0) of an ultra-short light pulse (P.sub.0) based on processing a number of substantially similar light pulses. The system includes an autocorrelation optical system adapted to receive the light pulses P.sub.0 and create from each light pulse two beams having an associated optical path length difference .DELTA.OPL. Providing a different .DELTA.OPL for each light pulse creates an autocorrelation interference pattern representative of an autocorrelation of the light pulse P.sub.0. An LED detector detects the autocorrelation interference pattern and generates therefrom an autocorrelation signal. A signal-processing unit forms from the autocorrelation signal a digital count signal representative of a number of counted peaks in the autocorrelation signal above the full-width half maximum. Control electronics unit causes the varying .DELTA.OPL and provides a difference signal (S.sub..DELTA.) representative of the .DELTA.OPL to the s

Imaging the Renner-Teller effect using laser-induced electron diffraction

Structural information on electronically excited neutral molecules can be indirectly retrieved, largely through pump-probe and rotational spectroscopy measurements with the aid of calculations. Here, we demonstrate the direct structural retrieval of neutral carbonyl disulfide (CS$_2$) in the B$^1$B$_2$ excited electronic state using laser-induced electron diffraction (LIED). We unambiguously identify the ultrafast symmetric stretching and bending of the field-dressed neutral CS$_2$ molecule with combined picometer and attosecond resolution using intrapulse pump-probe excitation and measurement. We invoke the Renner-Teller effect to populate the B$^1$B$_2$ excited state in neutral CS$_2$, leading to bending and stretching of the molecule. Our results demonstrate the sensitivity of LIED in retrieving the geometric structure of CS$_2$, which is known to appear as a two-center scatterer

Fluorescent nanodiamonds: past, present, and future

Multi-color fluorescent nanodiamonds (FNDs) containing a variety of color centers are promising fluorescent markers for biomedical applications. Compared to colloidal quantum dots and organic dyes, FNDs have the advantage of lower toxicity, exceptional chemical stability, and better photostability. They can be surface functionalized by techniques similar to those used for other nanoparticles. They exhibit a variety of emission wavelengths from visible to near infrared, with narrow or broad bandwidths depending on their color centers. In addition, some color centers can detect changes in magnetic fields, electric fields, and temperature. In this article review, we will discuss the current trends in FND’s development, including comparison to the early development of quantum dots. We will also highlight some of the latest advances in fabrication, as well as demonstrations of their use in bioimaging and biosensing

Surgeons' Ability to Predict the Extent of Surgery Prior to Cytoreductive Surgery With Hyperthermic Intraperitoneal Chemotherapy

Background: The extent of surgery (ES) during cytoreductive surgery with hyperthermic intraperitoneal chemotherapy (CRS + HIPEC) is a well-known risk factor for major postoperative morbidity. Interestingly, the reliability of surgeons to predict the ES prior to CRS + HIPEC is unknown. Methods: In this prospective, observational cohort study, five surgeons predicted the ES prior to surgery in all consecutive patients with peritoneal metastases (PM) who were scheduled for CRS + HIPEC between March 2018 and May 2019. After the preoperative work-up for CRS + HIPEC was completed, all surgeons independently predicted, for each individual patient, the resection or preservation of 22 different anatomical structures and the presence of a stoma post-HIPEC according to a standardized ES form. The actual ES during CRS + HIPEC was extracted from the surgical procedure report and compared with the predicted ES. Overall and individual positive (PPV) and negative predictive values (NPV) for each anatomical structure were calculated. Results: One hundred and thirty-one ES forms were collected from 32 patients who successfully underwent CRS + HIPEC. The number of resections was predicted correctly 24 times (18.3%), overestimated 57 times (43.5%), and underestimated 50 times (38.2%). Overall PPVs for the different anatomical structures ranged between 33.3 and 87.8%. Overall, NPVs ranged between 54.9 and 100%, and an NPV > 90% was observed for 12 anatomical structures. Conclusions: Experienced surgeons seem to be able to better predict the anatomical structures that remain in situ after CRS + HIPEC, rather than predict the resections that were necessary to achieve a complete cytoreduction

Lanthanide ions doped in vanadium oxide for sensitive optical glucose detection

Blood glucose monitoring is essential to avoid the unwanted consequences of glucose level fluctuations. Optical monitors are of special interest because they can be non-invasive. Among optical glucose sensors, fluorescent upconversion nanoparticles (UCNPs) have the advantage of good photostability, low toxicity, and exceptional autofluorescence suppression. However, to sense glucose, UCNPs normally need surface functionalization, and this can be easily affected by other factors in biological systems, and may also affect their ability for real-time sensing of both increasing and decreasing glucose levels. Here, we report YVO4 : Yb3+, Er3+@Nd3+core/shell UCNPs with Nd and Yb shell and GdVO4 : Yb3+, Er3+@Nd3+ core/shell UCNPs with Nd and Yb shell that show sensitive, reversible, and selective optical glucose detection without the need for any surface functionalization or modifications

Kinematically complete measurements of strong eld ionisation with mid-IR pulses

Recent observations of three unique peaks near 1 eV, 100 meV and 1 meV in the electron spectra generated by ionization using intense mid-IR pulses have challenged the current understanding of strong-field (SF) ionization. The results came as a surprise as they could not be reproduced by the standard version of the commonly used SF approximation. We present results showing the simultaneous measurement of all three low energy ranges at high resolution. This capability is possible due to a unique experimental combination of a high repetition rate mid-IR source, which allows probing deep in the quasi-static regime at high data rates, with a reaction microscope, which allows high resolution three dimensional imaging of the electron momentum distribution.Peer ReviewedPostprint (author's final draft

Quantum Electronics

Contains report on ten research projects split into three sections.Joint Services Electronics Program (Contract DAAG29-78-C-0020)National Science Foundation (Grant PHY77-07156)U. S. Air Force-Office of Scientific Research (Grant AFOSR-3042)National Science Foundation (Grant ENG77-24981

Nonlinear Effects in Pulse Propagation through Doppler-Broadened Closed-Loop Atomic Media

Nonlinear effects in pulse propagation through a medium consisting of four-level double-$\Lambda$-type systems are studied theoretically. We apply three continous-wave driving fields and a pulsed probe field such that they form a closed interaction loop. Due to the closed loop and the finite frequency width of the probe pulses the multiphoton resonance condition cannot be fulfilled, such that a time-dependent analysis is required. By identifying the different underlying physical processes we determine the parts of the solution relevant to calculate the linear and nonlinear response of the system. We find that the system can exhibit a strong intensity dependent refractive index with small absorption over a range of several natural linewidths. For a realistic example we include Doppler and pressure broadening and calculate the nonlinear selfphase modulation in a gas cell with Sodium vapor and Argon buffer gas. We find that a selfphase modulation of $\pi$ is achieved after a propagation of few centimeters through the medium while the absorption in the corresponding spectral range is small.Comment: 4 figure