Nanosecond laser systems

Al-doped ZnO (AZO) thin films were deposited on p-Si (100) by pulsed laser deposition from a composite ceramic target (ZnO:Al₂O₃) by using 355 nm laser at different O₂ background pressure and substrate temperature. Upon ablation at laser fluence of 2 Jcm⁻², plasma plume consists of Zn neutrals and ions, Al neutrals and O neutral are formed. As the O₂ background pressure increases from 3 Pa to 26 Pa, the energy of the plasma species are moderated. The results show that the ions density and velocity reduced significantly above 13 Pa. The velocity of the ions reduced from 14 kms⁻¹ to 11 kms⁻¹ at 13 Pa, while the ions energy reduced from 63 eV to 42 eV respectively. Below 13 Pa, crystalline and homogeneous AZO nanostructured films were formed. Above 13 Pa, the process results in low crystallinity films with higher porosity. The resistivity of the films also increases from 0.1 ohmcm to 24 ohmcm as the pressure increased. At fixed O₂ background pressure of 3 Pa, the adatom mobility of atoms on the substrates is altered by substrate heating. The resistivity of the films decreased to 10^–3 ohmcm when the substrates are heated to 100 °C–300 °C during deposition. The films with highest carrier density of 10²⁰ cm⁻³ and carrier mobility of 13 cmV⁻¹ s⁻¹ are achieved at 200 °C.

Direct generation of gold nanoparticles on ITO glass using a nanosecond laser is presented and the electrochemical properties of the gold modified ITO electrodes for detection of the ascorbic acid are analyzed. Gold nanoparticles were generated by nanosecond laser pulse irradiation of thin, 3 – 30 nm thick, gold films. It was found that diameters and the number of generated nanoparticles per unit area strongly depends on the thickness of the gold film when it is less than 10 nm. Furthermore, experiments have shown that the influence of laser processing parameters (the laser pulse energy and pulse number) to the size, the distribution and the area density of generated gold nanoparticles on ITO glass is negligible. Characterization of the electrochemical properties of the gold modified ITO electrodes by nanosecond laser showed that the fabricated electrodes could be employed in electrochemical sensing. Therefore, the demonstrated generation of gold nanoparticles on ITO by using the nanosecond laser approach opens new opportunities for the development of highly sensitive and low-cost electrochemical sensors.

Light is an exceptional external stimulus for establishing precise control over the properties and functions of chemical and biological systems, which is enabled through the use of molecular photoswitches. Ideal photoswitches are operated with visible light only, show large separation of absorption bands and are functional in various solvents including water, posing an unmet challenge. Here we show a class of fully-visible-light-operated molecular photoswitches, Iminothioindoxyls (ITIs) that meet these requirements. ITIs show a band separation of over 100 nm, isomerize on picosecond time scale and thermally relax on millisecond time scale. Using a combination of advanced spectroscopic and computational techniques, we provide the rationale for the switching behavior of ITIs and the influence of structural modifications and environment, including aqueous solution, on their photochemical properties. This research paves the way for the development of improved photo-controlled systems for a wide variety of applications that require fast responsive functions.

The marked increase in the incidence of melanoma coupled with the rapid drop in the survival rate after metastasis has promoted the investigation into improved diagnostic methods for melanoma. High-frequency ultrasound (US), optical coherence tomography (OCT), and photoacoustic imaging (PAI) are three potential modalities that can assist a dermatologist by providing extra information beyond dermoscopic features. In this study, we imaged a swine model with spontaneous melanoma using these modalities and compared the images with images of nearby healthy skin. Histology images were used for validation.

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 optical coherence tomography (OCT) with 2 nm axial resolution using broadband soft X-ray radiation (SXR) from a compact laser plasma light source. The laser plasma was formed by the interaction of nanosecond laser pulses with a gaseous target in a double stream gas puff target approach. The source was optimized for efficient SXR emission from the krypton/helium gas puff target in the 2 to 5 nm spectral range, encompassing the entire “water-window” spectral range from 2.3 nm to 4.4 nm wavelength. The coherence parameters of the SXR radiation allowed for the OCT measurements of a bulk multilayer structure with 10 nm period and 40% bottom layer thickness to period ratio, with an axial resolution of about 2 nm and detect multilayer interfaces up to a depth of about 100 nm. The experimental data are in agreement with OCT simulations performed on ideal multilayer structure. In the paper, detailed information about the source, its optimization, the optical system, OCT measurements and the results are presented and discussed.

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.

In this paper, experiments are described in which cylindrical vacuum insulator samples and samples inclined at 45° relative to the cathode were stressed by microsecond timescale high-voltage pulses and illuminated by focused UV laser beam pulses. In these experiments, we were able to distinguish between flashover initiated by the laser producing only photo-electrons and when plasma is formed. It was shown that flashover is predominantly initiated near the cathode triple junction. Even dense plasma formed near the anode triple junction does not necessarily lead to vacuum surface flashover. The experimental results directly confirm our conjecture that insulator surface breakdown can be avoided by preventing its initiation [J. G. Leopold et al., Phys. Rev. ST Accel. Beams 10, 060401 (2007)] and complement our previous experimental results [J. Z. Gleizer et al., IEEE Trans. Dielectr. Electr. Insul. 21, 2394 (2014) and J. Z. Gleizer et al., J. Appl. Phys. 117, 073301 (2015)].

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.