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Abstract Heat acclimation/acclimatisation (HA) mitigates heat-related decrements in physical capacity and heat-illness risk and is a widely advocated countermeasure for individuals operating in hot environments. The efficacy of HA is typically quantified by assessing the thermo-physiological responses to a standard heat acclimation state test (i.e. physiological biomarkers), but this can be logistically challenging, time consuming, and expensive. A valid molecular biomarker of HA would enable evaluation of the heat-adapted state through the sampling and assessment of a biological medium. This narrative review examines candidate molecular biomarkers of HA, highlighting the poor sensitivity and specificity of these candidates and identifying the current lack of a single ‘standout’ biomarker. It concludes by considering the potential of multivariable approaches that provide information about a range of physiological systems, identifying a number of challenges that must be overcome to develop a valid molecular biomarker of the heat-adapted state, and highlighting future research opportunities.

Results of angle-resolved electron spectroscopy of near-threshold photoionization of Ne atoms by combined femtosecond extreme ultraviolet and near infrared fields are presented. The dressed-electron spectra show an energetic distribution into so-called sidebands, being separated by the photon energy of the dressing laser. Surprisingly, for the low kinetic energy (few eV) sidebands, the photoelectron energy varies as a function of the emission angle. Such behavior has not yet been observed in sideband creation and has not been predicted in commonly used theoretical descriptions such as strong field approximation and soft photon approach. Describing the photoionization with a time-dependent Schrödinger equation allows a qualitative description of the observed effect, as well as the prediction of fine structure in the sideband distribution.

Arbitrary manipulation of the temporal and spectral properties of x-ray pulses at free-electron lasers would revolutionize many experimental applications. At the Linac Coherent Light Source at Stanford National Accelerator Laboratory, the momentum phase-space of the free-electron laser driving electron bunch can be tuned to emit a pair of x-ray pulses with independently variable photon energy and femtosecond delay. However, while accelerator parameters can easily be adjusted to tune the electron bunch phase-space, the final impact of these actuators on the x-ray pulse cannot be predicted with sufficient precision. Furthermore, shot-to-shot instabilities that distort the pulse shape unpredictably cannot be fully suppressed. Therefore, the ability to directly characterize the x-rays is essential to ensure precise and consistent control. In this work, we have generated x-ray pulse pairs via electron bunch shaping and characterized them on a single-shot basis with femtosecond resolution through time-resolved photoelectron streaking spectroscopy. This achievement completes an important step toward future x-ray pulse shaping techniques.

Three light-induced galvanic contributions to the real optogalvanic (OG) signal were studied in a hollow cathode discharge (HCD). The photoelectron emission (PE) from the cathode surface with a sub-breakdown bias applied, and hence no discharge present, was measured within the framework of an OG experimental arrangement. The PE component in a real OG measurement was found to manifest itself as an instrumental effect along with the effect of nonresonant ionization. The convolution of these components was determined experimentally as an instrumental function, and a deconvolution procedure to determine the actual OG signal was developed. The transient characteristics of the OG circuit were analysed by time-deconvolution of the measured OG signal, and they turned out to be dependent on the operating HCD I–V point. In addition, the polarization of the light beam irradiating the HCD was found to influence the OG signal. [ABSTRACT FROM AUTHOR]

We report here the results of a study of polarisation resolved emission from a laser produced copper plasma. We found that in the case of such a plasma, the degree of polarisation was higher for a background pressure of 1 × 10−2 mbar than for 1 × 10−5 mbar, but the time evolution of this parameter was similar for both. Optical diagnostics revealed differences in the electron temperature and density also. A collisional radiative model was then employed to calculate the time varying rates of both radiative and 3-body recombination. We found that the rates were strongly polarisation and time dependent for our plasma and thus we suggest that both 3-body and radiative recombination play a role in the ultimate optical anisotropy of the plasma. [ABSTRACT FROM AUTHOR]

The design and implementation of a low cost interferometric autocorrelator with no moving parts is discussed. It is found that the device is optically simple, uses low cost components and self aligns. The device is used to measure the interferometric autocorrelation of an 800 nm Ti:Sapphire laser pulse produced from an 80 MHz oscillator. The theory and experiment of the design is discussed and compared to results from a commercial autocorrelator. The device is intended for use where pulse to pulse monitoring of the temporal duration is required. [ABSTRACT FROM AUTHOR]

Measurements of the total ion emission from a pair of colliding laser-produced aluminium plasmas were obtained with the aid of a Faraday cup detector. The energy profile width at half height of the kinetic energy distribution for ions emitted normal to the target was found to be 30% narrower for colliding plasmas compared with a single plasma. Similar to ion emission from single plumes, the mean ion kinetic energy is observed to increase with the energy of the incident laser pulse. However, the width of the ion energy distribution increases at a significantly slower rate than in the single plume case. [ABSTRACT FROM AUTHOR]

Charged particle sources require beam transport techniques specific to the application for optimum operation. The complexity of techniques increases as the degree of ionization and kinetic energy of charged particles increases. The Dublin City University laser ion source (DCU-LIS) utilizes a short field region (L = 48 mm) to maximize the average charge state and peak current extracted, thus ion extraction occurs at 'high pressure'. The presence of large space-charge forces, high average plasma plume temperature and the expansion dynamics of laser-generated plasmas results in significant divergence of the ion bunch upon injection into the drift tube. To facilitate efficient beam transport, and to maximize system throughput, we employ a rather unique electrostatic transport system, termed as 'continuous einzel array' (CEA). Ion electrodynamics in such a system exhibit a number of distinct features which modify the system performance and alter the expected distribution of kinetic energies (KE), the times of flight and ion bunch diameters. System scalability in regard to beam kinetic energy is also important. In this paper the superior performance of the LIS equipped with a CEA is compared with a traditional einzel lens electrostatic beam transport system based on the usual 3-element and also a 5-element lens system. [ABSTRACT FROM AUTHOR]

First experiments on atomic photoionization and molecular dissociation have been performed by taking advantage of the unprecedented characteristics of the free electron laser in Hamburg (FLASH) combined with a separate near-infrared (NIR) femtosecond laser. In a series of two-colour experiments, the photoionization of rare gases in the presence of a strong NIR dressing field as well as the polarization dependence of this process were investigated systematically. A detailed analysis of the partial cross sections for the two-colour two-photon ionization process was carried out for low dressing fields. Higher dressing fields gave rise to multi-photon processes, which were observed and analysed without undesirable interferences, a beneficial consequence of the monochromaticity of the FLASH radiation. The experimental results were compared with theoretical descriptions for two-colour above-threshold ionization obtained by employing second-order perturbation theory and the 'soft-photon' approximation. In addition, complementary information was obtained on the sequential two-photon double ionization of Ne, which was made possible by the short and intense FLASH pulses. As a starting point for future time-resolved studies of molecular dissociation, a proof-of-principle experiment on the hydrogen diatomic system was carried out. In a typical pump-probe arrangement, excited neutral fragments, which were formed during photo-induced dissociation by the FLASH radiation, were identified via single- and multi-photon ionization induced by the time-delayed optical laser. [ABSTRACT FROM AUTHOR]

The photoabsorption spectra of lead and bismuth ions have been recorded using the dual laser plasma (DLP) technique in the photon energy range 30-66 eV. The experimental observations and theoretical calculations are focused on the 5d inner-shell excitations of the Hg I like ions of lead (Pb III) and bismuth (Bi IV). With the aid of Hartree-Fock calculations in the jj coupling scheme, we have identified over 30 new lines in both ions. As a result of the new measurements in Bi IV, the previously determined first ionization potential of Bi III has been increased from 45.32 eV to 45.36 eV. [ABSTRACT FROM AUTHOR]