Nanosecond laser systems

The new C-2W Thomson scattering (TS) diagnostic consists of two individual subsystems for monitoring electron temperature (T_e) and density (n_e): one system in the central region is currently operational, and the second system is being commissioned to monitor the open field line region. Validating the performance of the TS’s custom designed system components and unique calibration of the detection system and diagnostic as a whole is crucial to obtaining high precision T_e and n_e profiles of C-2W’s plasma. The major components include a diode-pumped Nd:YAG laser which produces 35 pulses at up to 20 kHz, uniquely designed collection lenses with a fast numerical aperture, and uniquely designed polychromators with filters sets to optimize a T_e ranging from 10 eV to 2 keV. This paper describes the design principles and techniques used to characterize the main components of the TS diagnostic on C-2W, as well as the results of Rayleigh scattering calibrations performed for the whole system response.

We optimized the parameters of a laser-produced plasma source based on a solid-state Nd: YAG laser (λ = 1.06 nm, pulse duration 4 ns, energy per pulse up to 500 mJ, repetition rate 10 Hz, lens focus distance 45 mm, maximum power density of laser radiation in focus 9 × 10¹¹ W/cm²) and a double-stream Xe/He gas jet to obtain a maximum of radiation intensity around 11 nm wavelength. It was shown that the key factor determining the ionization composition of the plasma is the jet density. With the decreased density, the ionization composition shifts toward a smaller degree of ionization, which leads to an increase in emission peak intensity around 11 nm. We attribute the dominant spectral feature centred near 11 nm originating from an unidentified 4d-4f transition array in Xe^+10…+13 ions. The exact position of the peak and the bandwidth of the emission line were determined. We measured the dependence of the conversion efficiency of laser energy into an EUV in-band energy with a peak at 10.82 nm from the xenon pressure and the distance between the nozzle and the laser focus. The maximum conversion efficiency (CE) into the spectral band of 10 – 12 nm measured at a distance between the nozzle and the laser beam focus of 0.5 mm was CE = 4.25 ± 0.30%. The conversion efficiencies of the source in-bands of 5 and 12 mirror systems at two wavelengths of 10.8 and 11.2 nm have been evaluated; these efficiencies may be interesting for beyond extreme ultraviolet lithography.

We present a broadband optical parametric chirped pulse amplification (OPCPA) system delivering 4 J pulses at a repetition rate of 5 Hz. It will serve as a frontend for the 1.5 kJ, <150 fs, 10 PW laser beamline currently under development by a consortium of National Energetics and Ekspla. The spectrum of the OPCPA system is precisely controlled by arbitrarily generated waveforms of the pump lasers. To fully exploit the high flexibility of the frontend, we have developed a 1D model of the system and an optimization algorithm that predicts suitable pump waveform settings for a desired output spectrum. The OPCPA system is shown to have high efficiency, a high-quality top-hat beam profile, and an output spectrum demonstrated to be shaped consistently with the theoretical model.

TAE Technologies’ newly constructed C-2W experiment aims to improve the ion and electron temperatures in a sustained field-reversed configuration plasma. A suite of Thomson scattering systems has been designed and constructed for electron temperature and density profile measurements. The systems are designed for electron densities of 1 × 10¹² cm⁻³ to 2 × 10¹⁴ cm⁻³ and temperature ranges from 10 eV to 2 keV. The central system will provide profile measurements of T_e and n_e at 16 radial locations from r = −9 cm to r = 64 cm with a temporal resolution of 20 kHz for 4 pulses or 1 kHz for 30 pulses. The jet system will provide profile measurements of T_e and n_e at 5 radial locations in the open field region from r = −5 cm to r = 15 cm with a temporal resolution of 100 Hz. The central system and its components have been characterized, calibrated, installed, and commissioned. A maximum-likelihood algorithm has been applied for data processing and analysis.

In this work, we present a compact laser-produced plasma source of X-rays, developed and characterized for application in soft X-ray contact microscopy (SXCM). The source is based on a double stream gas puff target, irradiated with a commercially available Nd:YAG laser, delivering pulses with energy up to 740 mJ and 4 ns pulse duration at 10 Hz repetition rate. The target is formed by pulsed injection of a stream of high-Z gas (argon) into a cloud of low Z-gas (helium) by using an electromagnetic valve with a double nozzle setup. The source is designed to irradiate specimens, both in vacuum and in helium atmosphere with nanosecond pulses of soft X-rays in the ‘‘water-window” spectral range. The source is capable of delivering a photon fluence of about 1.09 x 10³ photon/µm²/pulse at a sample placed in vacuum at a distance of about 20 mm downstream the source. It can also deliver a photon fluence of about 9.31 x 10² – photons/µm²/pulse at a sample placed in a helium atmosphere at the same position. The source design and results of the characterization measurements as well as the optimization of the source are presented and discussed. The source was successfully applied in the preliminary experiments on soft X-ray contact microscopy and images of microstructures and biological specimens with ~80 nm half-pitch spatial resolution, obtained in helium atmosphere, are presented.

Laser-produced plasmas are intense sources of XUV radiation that can be suitable for different applications such as extreme ultraviolet lithography, beyond extreme ultraviolet lithography and water window imaging. In particular, much work has focused on the use of tin plasmas for extreme ultraviolet lithography at 13.5 nm. We have investigated the spectral behavior of the laser produced plasmas formed on closely packed polystyrene microspheres and porous alumina targets covered by a thin tin layer in the spectral region from 2.5 to 16 nm. Nd:YAG lasers delivering pulses of 170 ps (Ekspla SL312P )and 7 ns (Continuum Surelite) duration were focused onto the nanostructured targets coated with tin. The intensity dependence of the recorded spectra was studied; the conversion efficiency (CE) of laser energy into the emission in the 13.5 nm spectral region was estimated. We have observed an increase in CE using high intensity 170 ps Nd:YAG laser pulses as compared with a 7 ns pulse.

We have observed extreme ultraviolet (EUV) spectra from terbium (Tb) ions in optically thin and thick plasmas for a comparative study. The experimental spectra are recorded in optically thin, magnetically confined torus plasmas and dense laser-produced plasmas (LPPs). The main feature of the spectra is quasicontinuum emission with a peak around 6.5-6.6 nm, the bandwidth of which is narrower in the torus plasmas than in the LPPs. A comparison between the two types of spectra also suggests strong opacity effects in the LPPs. A comparison with the calculated line strength distributions gives a qualitative interpretation of the observed spectra.

Laser-induced breakdown spectroscopy (LIBS) technology is an appealing technique compared with many other types of elemental analysis because of the fast response, high sensitivity, real-time, and noncontact features. One of the challenging targets of LIBS is the enhancement of the detection limit. In this study, the detection limit of gas-phase LIBS analysis has been improved by controlling the pressure and laser pulse width. In order to verify this method, low-pressure gas plasma was induced using nanosecond and picosecond lasers. The method was applied to the detection of Hg. The emission intensity ratio of the Hg atom to NO (I_Hg/ I_NO) was analyzed to evaluate the LIBS detection limit because the NO emission (interference signal) was formed during the plasma generation and cooling process of N₂ and O₂ in the air. It was demonstrated that the enhancement of I_Hg/I_NO arose by decreasing the pressure to a few kilopascals, and the I_Hg/I_NO of the picosecond breakdown was always much higher than that of the nanosecond breakdown at low buffer gas pressure. Enhancement of I_Hg/I_NO increased more than 10 times at 700 Pa using picosecond laser with 35 ps pulse width. The detection limit was enhanced to 0.03 ppm (parts per million). We also saw that the spectra from the center and edge parts of plasma showed different features. Comparing the central spectra with the edge spectra, I_Hg/I_NO of the edge spectra was higher than that of the central spectra using the picosecond laser breakdown process.

Breast cancer screening with mammography is less effective in women with dense breast tissue, prompting the use of ultrasound (US) imaging. While two- (2D) and three-dimensional (3D) US improve cancer detection, their low specificity leads to frequent unnecessary biopsies. Operator dependence on 2D US has led to the development of 3D automated breast volume scanners (ABVS), but challenges remain in distinguishing benign from malignant lesions. We developed a 3D photoacoustic and ultrasound (PAUS)–ABVS system that integrates a large field-of-view, 768-element transducer to improve diagnostic accuracy. In a clinical study of 61 patients with 36 benign and 30 malignant lesions, multispectral photoacoustic imaging was used to measure blood volume and oxygen saturation within lesions. When combined with standard US BI-RADS (breast imaging reporting and data system) scores, the system achieved a sensitivity of 96.7% and specificity of 66.7%. This performance matched the best outcomes of 2D PAUS and outperformed conventional US. Our results suggest that the PAUS-ABVS can support more accurate breast cancer diagnosis while reducing unnecessary biopsies.

Image-guided phototheranostics, including photothermal therapy and photoacoustic imaging using plasmonic nanoparticles, has attracted attention due to its remarkable photothermal conversion effects. In particular, considering the several benefits of biocompatibility, unique plasmon resonance, and tunable optical properties, gold nanoparticles of various shapes have been widely utilized as phototheranostic agents. However, applications in the near-infrared window have been limited due to the tendency of anisotropic gold nanoparticles to transform into spherical shapes under repetitive laser irradiation, which cause a shift in the localized surface plasmon resonance peak and reduces photothermal stability. To address these limitations, we introduce an Fe layer between Au nanodiscs to synthesize Au/Fe/Au trilayer uniform structured nanodiscs (AuFeAuNDs) using nanoimprint lithography. This approach aims to improve photostability and endow a magnetic targeting ability, enabling more accurate spatiotemporal regulation. The AuFeAuNDs primarily function as photothermal therapy agents and also serve as chemodynamic agents via the Fenton reaction specifically within the tumor microenvironment, which induces ferroptosis. Moreover, the AuFeAuNDs trigger immunogenic cell death following photothermal therapy. This study demonstrates applications of magnetic-targeted AuFeAuNDs for photoacoustic imaging-guided, spatiotemporal-controlled photothermal therapy, chemodynamic therapy, and immune modulation to bolster anti-tumor immune responses in cancer treatment.

Fabry–Perot (FP) ultrasound sensors are a class of optical ultrasound sensors used in photoacoustic tomography (PAT) and other applications. Conventionally, an FP ultrasound sensor comprises an ultrasonically compressible planar microcavity, locally interrogated by a focused Gaussian beam. One way to increase the sensitivity could be to replace this beam with a Bessel beam. The rationale is twofold. First, as a Bessel beam’s wavefront better matches the modes of the planar microcavity, this could increase the -factor, leading to higher sensitivity. Second, as a Bessel beam provides a focused spatial structure—a central core surrounded by concentric rings—it might retain the ability to locally interrogate the sensor. To explore this idea, we developed an experimental system featuring a custom FP ultrasound sensor interrogated by a Bessel beam and evaluated its on-axis sensitivity, directivity, and image resolution when performing PAT. For comparison, we measured the same characteristics using a conventional focused Gaussian beam with a spot size similar to the core of the Bessel beam. As anticipated, the Bessel beam provided a higher ultrasonic on-axis sensitivity. However, the directivity and spatial resolution were degraded, suggesting that the Bessel beam yielded a larger acoustic element. We conclude that it is feasible to increase the sensitivity of an FP ultrasound sensor using a Bessel beam. Further work is required to establish whether differently designed Bessel beams could concurrently offer a smaller acoustic element.

Abstract Early-stage stroke monitoring enables timely intervention that is crucial to minimizing neuronal damage and increasing the extent of recovery. By monitoring collateral circulation and neovascularization after ischemic stroke, the natural recovery process can be better understood, optimize further treatment strategies, and improve the prognosis. Photoacoustic computed tomography (PACT), a non-invasive imaging modality that captures multiparametric high-resolution images of vessel structures, is well suited for evaluating cerebrovascular structures and their function. Here 3D multiparametric transcranial PACT is implemented to monitor the early stage of a photothrombotic (PT)-stroke model in living rats. New vessels in the PT-induced region are successfully observed using PACT, and these observations are confirmed by histology. Then, using multiparametric PACT, it is found that the SO2 in the ischemic area decreases while the SO2 in newly formed vessels increases, and the SO2 in the PT region also recovers. These findings demonstrate PACT\’s remarkable ability to image and monitor cerebrovascular morphologic and physiological changes. They highlight the usefulness of whole-brain PACT as a potentially powerful tool for early diagnosis and therapeutic decision-making in treating ischemic stroke.

Superfluorescence (SF) in lanthanide doped upconversion nanoparticles (UCNPs) is a room-temperature quantum phenomenon, first discovered in 2022. In a SF process, the many emissive lanthanide ions within a single UCNP are coherently coupled by an ultra-short (ns or fs) high-power excitation laser pulse. This leads to a superposition of excited emissive states which decrease the emissive lifetime of the UCNP by a factor proportional to the square of the number of lanthanide ions which are coherently coupled. This results in a dramatic decrease in UCNP emission lifetime from the μs regime to the ns regime. Thus SF offers a tantalizing prospect to achieving superior upconversion photon flux in upconversion materials, with potential applications such as imaging and sensing. This perspective article contextualizes how SF-UCNPs can be regarded as a second generation quantum technology, and notes several challenges, opportunities, and open questions for the development of SF-UCNPs.

Photoacoustic tomography (PAT) has the potential to become a widely used imaging tool in preclinical studies of small animals. This is because it can provide non-invasive, label free images of whole-body mouse anatomy, in a manner which is challenging for more established imaging modalities. However, existing PAT scanners are limited because they either do not implement a full 3-D tomographic reconstruction using all the recorded photoacoustic (PA) data and/or do not record the available 3-D PA time-series data around the mouse with sufficiently high spatial resolution ( ∼100μ m), which compromises image quality in terms of resolution, imaging depth and the introduction of artefacts. In this study, we address these limitations by demonstrating an all-optical, multi-view Fabry-Perot based scanner for whole body small animal imaging. The scanner densely samples the acoustic field with a large number of detection points (>100,000), evenly distributed around the mouse. The locations of the detection points were registered onto a common coordinate system, before a tomographic reconstruction using all the recorded PA time series was implemented. This enabled the acquisition of high resolution, whole-body PAT images of ex-vivo mice, with anatomical features visible across the entire cross section.

The clinical assessment of microvascular pathologies (in diabetes and in inflammatory skin diseases, for example) requires the visualization of superficial vascular anatomy. Photoacoustic tomography (PAT) scanners based on an all-optical Fabry–Perot ultrasound sensor can provide highly detailed 3D microvascular images, but minutes-long acquisition times have precluded their clinical use. Here we show that scan times can be reduced to a few seconds and even hundreds of milliseconds by parallelizing the optical architecture of the sensor readout, by using excitation lasers with high pulse-repetition frequencies and by exploiting compressed sensing. A PAT scanner with such fast acquisition minimizes motion-related artefacts and allows for the volumetric visualization of individual arterioles, venules, venous valves and millimetre-scale arteries and veins to depths approaching 15 mm, as well as for dynamic 3D images of time-varying tissue perfusion and other haemodynamic events. In exploratory case studies, we used the scanner to visualize and quantify microvascular changes associated with peripheral vascular disease, skin inflammation and rheumatoid arthritis. Fast all-optical PAT may prove useful in cardiovascular medicine, oncology, dermatology and rheumatology.

Photoacoustic imaging offers high spatial resolution, imaging depth, and molecular information, emerging as a promising biomedical imaging modality. In particular, when using exogenous contrast, the advantages of photoacoustic imaging can be more effectively utilized in preclinical and clinical studies. We provide a novel approach to screen and identify efficient photoacoustic performance as contrast agents of the metals. To accomplish this, we introduce a novel figure of merit that quantifies the potential performance of contrast agents. As a result of the quantification, we discover that Ti nanodiscs outperform Pt nanodiscs in terms of photoacoustic ability, which shows a similar level to Au nanodiscs. We compare these results by performing a photoacoustic phantom imaging experiment. The photoacoustic performance of the three materials is compared by comparing the signal intensity of the materials measured on the photoacoustic image for various wavelengths. The imaging results further support our findings, demonstrating the superior performance of Ti nanodiscs as contrast agents.

Photonic-based methods are crucial in biology and medicine due to their non-invasive nature, allowing remote measurements without affecting biological specimens. The study of diatoms using advanced photonic methods remains a relatively underexplored area, presenting significant opportunities for pioneering discoveries. This research provides a comprehensive analysis of marine diatoms, specifically Nitzschia sp., across varying salinity levels, integrating fluorescence lifetime imaging microscopy (FLIM), combined photoacoustic and fluorescence tomographies (PAFT), and ultrastructural examinations using transmission electron microscopy. Key findings include a systematic shift in the mean fluorescence lifetime from 570 ps at 20‰ to 940 ps at 80‰, indicating functional adaptations in chlorophyll molecules within light-harvesting complexes. At 60‰ salinity, anomalies are observed in the development of silica valves and polysaccharide layers, suggesting abnormalities in valve morphogenesis. Lipid droplets within the cells display a minimum diameter at 40‰, indicating metabolic adjustments to osmotic stress. The intensity of both fluorescence and photoacoustic signals increases with increasing salinity levels. These insights enhance understanding of the ecological implications of salinity stress on diatom communities and pave the way for future research on leveraging the unique adaptive mechanisms of microalgae for environmental monitoring and sustainable biotechnological applications.

Lewis hunting reaction refers to the alternating cold-induced vasoconstriction and dilation in extremities, whose underlying mechanism is complex. While numerous studies reported this intriguing phenomenon by measuring cutaneous temperature fluctuation under cold exposure, few of them tracked peripheral vascular responses in real-time, lacking a non-invasive and quantitative imaging tool. To better monitor hunting reaction and diagnose relevant diseases, we developed a hybrid photoacoustic ultrasound (PAUS) tomography system to monitor finger vessels’ dynamic response to cold, together with simultaneous temperature measurement. We also came out a standard workflow for image analysis with self-defined indices. In the small cohort observational study, vascular changes in the first cycle of hunting reaction were successfully captured by the image series and quantified. Time difference between vasodilation and temperature recovery was noticed and reported for the first time, thanks to the unique capability of the PAUS imaging system in real-time and continuous vascular monitoring. The developed imaging system and indices enabled more objective and quantitative monitoring of peripheral vascular activities, indicating its great potential in numerous clinical applications.