Search

We present a simple and easy-to-implement Graphics Processing Unit (GPU)-accelerated routine to numerically simulate the propagation of ultrashort and intense laser pulses as they interact with a medium. The routine is based on the solution of Maxwell's wave equation in the frequency domain with an extended Crank–Nicolson algorithm implemented in the Nvidia CUDA C++ programming language. The main advantages of our method are its significant speed-up factor and its ease of implementation, requiring only basic knowledge of CUDA and C++. In this article, we review the strong-field wave equations to be solved and their discretization and demonstrate how to implement a numerical solver for them on an Nvidia GPU. We show the results of the simulation of a near-infrared laser pulse propagating through a partially ionized atomic gas and discuss the performance of our GPU-accelerated scheme. Compared to a naïve central processing unit implementation of the same routine, our GPU-accelerated version is up to 198 times faster in standard regimes. [ABSTRACT FROM AUTHOR]

The ablation of solid tin surfaces by a 800-nanometer-wavelength laser is studied for a pulse length range from 500 fs to 4.5 ps and a fluence range spanning from 0.9 to 22 J/cm2. The ablation depth and volume are obtained employing a high-numerical-aperture optical microscope, while the ion yield and energy distributions are obtained from a set of Faraday cups set up under various angles. We found a slight increase of the ion yield for an increasing pulse length, while the ablation depth is slightly decreasing. The ablation volume remained constant as a function of pulse length. The ablation depth follows a two-region logarithmic dependence on the fluence, in agreement with the available literature and theory. In the examined fluence range, the ion yield angular distribution is sharply peaked along the target normal at low fluences but rapidly broadens with increasing fluence. The total ionization fraction increases monotonically with fluence to a 5%-6% maximum, which is substantially lower than the typical ionization fractions obtained with nanosecond-pulse ablation. The angular distribution of the ions does not depend on the laser pulse length within the measurement uncertainty. These results are of particular interest for the possible utilization of fs-ps laser systems in plasma sources of extreme ultraviolet light for nanolithography. [ABSTRACT FROM AUTHOR]

We demonstrate a method for efficient lensless imaging using ultra-broadband light sources. By using a pair of time-delayed, coherent pulses in a Fourier-transform scheme, spectrally resolved diffraction patterns are obtained throughout the entire spectrum of the incident light source. We perform a proof-of-principle experiment using an octave-spanning visible light source, and obtain images of a holographic test sample with near-diffraction limited resolution. Our approach provides a promising route towards efficient high-resolution imaging using table-top high-harmonic soft-X-ray sources.

Experimental scaling relations of the optical depth are presented for the emission spectra of a tin-droplet-based, 1-μm-laser-produced plasma source of extreme-ultraviolet (EUV) light. The observed changes in the complex spectral emission of the plasma over a wide range of droplet diameters (16–65 μm) and laser pulse durations (5–25 ns) are accurately captured in a scaling relation featuring the optical depth of the plasma as a single, pertinent parameter. The scans were performed at a constant laser intensity of 1.4 × 1011 W/cm2, which maximizes the emission in a 2% bandwidth around 13.5 nm relative to the total spectral energy, the bandwidth relevant for industrial EUV lithography. Using a one-dimensional radiation transport model, the relative optical depth of the plasma is found to linearly increase with the droplet size with a slope that increases with the laser pulse duration. For small droplets and short laser pulses, the fraction of light emitted in the 2% bandwidth around 13.5 nm relative to the total spectral energy is shown to reach high values of more than 14%, which may enable conversion efficiencies of Nd:YAG laser light into—industrially—useful EUV radiation rivaling those of current state-of-the-art CO2-laser-driven sources. [ABSTRACT FROM AUTHOR]

The light from one single frequency cw laser was employed in a double saturation spectroscopy experiment to record high resolution spectra of 129I2 and 127I129I together with spectra of 127I2 which is used as a simultaneous frequency reference. Two separate saturation spectroscopy set ups were used. The frequencies of lines of 129I2 and 127I129I were determined with respect to lines of 127I2. More than 380 frequency differences between lines of 127I2 and of the other isotopomers have been included in the data set. By a direct potential fit a precise description of the potential energy curves of the B and the X state and of effective Born-Oppenheimer correction functions valid for all three isotopomers of I2 are given. [ABSTRACT FROM AUTHOR]

We present a systematic numerical design and performance study of an ultra-broadband noncollinear optical parametric chirped pulse amplification (NOPCPA) system. Using a split-step Fourier approach, we model a three-stage amplifier system which is designed for the generation of 7 fs pulses with multi-terawatt peak intensity. The numerical results are compared with recent experimental data. Several important aspects and design parameters specific to NOPCPA are identified, and the values of these parameters required to achieve optimal working conditions are investigated. We identify and analyze wavelength-dependent gain saturation effects, which are specific to NOPCPA and have a strong influence on the parametric amplification process. [ABSTRACT FROM AUTHOR]

We have performed high-precision spectroscopy on the first resonance line of Mg i at 285 nm. This measurement is motivated by the recent studies comparing observed quasar absorption lines with laboratory measurements in the search for a possible variation of the fine structure constant α. The Mg transition is excited using the up-converted radiation of an injection-seeded Ti : sapphire pulsed laser system, while the frequency of the continuous wave seed light is measured using a femtosecond frequency comb laser. The line positions of the isotopes are fully resolved and have accuracies better than . Using terrestrial abundances for the Mg isotopes 24Mg : 25Mg : 26Mg of 78.99 : 10.00 : 11.01, we determine the composite line wavenumber to be 35 051.2808(2) cm−1, which can be compared to the astronomical observations where the isotopic shifts are unresolved. [ABSTRACT FROM AUTHOR]

In a double saturation spectroscopy experiment, using the radiation from one single frequency cw laser, the spectra of 129 I 2 and 127 I 129 I from one saturation setup were recorded simultaneously and with respect to the spectrum of 127 I 2 from another setup while tuning the laser. The hyperfine patterns of 129 I 2 and 127 I 129 I were analysed to determine the nuclear electric quadrupole interaction and the nuclear spin–rotation interaction parameters. Models are presented describing the observations and giving reliable predictions for the hyperfine parameters of all isotopomers. [ABSTRACT FROM AUTHOR]

The evolution of the carrier-envelope offset phase ϕCEO of a 10-fs Ti:Sapphire laser has been traced on time scales from microseconds to seconds using various techniques. Precise locking of this phase has been achieved down to an rms deviation of 1/40 of an optical cycle. Stability measurements have been performed independently of the feedback loop, focusing on the phase jitter introduced by the feedback loop itself, the pump laser, and a prism compressor. It is shown that a multi-mode pump laser introduces more phase noise on ϕCEO than a single-mode pump laser. [ABSTRACT FROM AUTHOR]

The fundamental ground tone vibration of H2, HD, and D2 is determined to an accuracy of 2 × 10-4 cm-1 from Doppler-free laser spectroscopy in the collisionless environment of a molecular beam. This rotationless vibrational splitting is derived from the combination difference between electronic excitation from the X¹Σg+, v = 0, and v = 1 levels to a common EF¹Σg+, v = 0 level. Agreement within 1σ between the experimental result and a full ab initio calculation provides a stringent test of quantum electrodynamics in a chemically bound system. [ABSTRACT FROM AUTHOR]

Nuclear-spin-symmetry conservation makes the observation of transitions between quantum states of ortho- and para-H2 extremely challenging. Consequently, the energy-level structure of H2 derived from experiment consists of two disjoint sets of level energies, one for para-H2 and the other for ortho-H2. We use a new measurement of the ionization energy of para-H2 [EI(H2)/(hc)=124 417.491 098(31) cm-1] to determine the energy separation [118.486770(50) cm-1] between the ground states of para- and ortho-H2 and thus link the energy-level structure of the two nuclear-spin isomers of this fundamental molecule. Comparison with recent theoretical results [M. Puchalski et al., Phys. Rev. Lett. 122, 103003 (2019)] enables the derivation of an upper bound of 1.5 MHz for a hypothetical global shift of the energy-level structure of ortho-H2 with respect to that of para-H2. [ABSTRACT FROM AUTHOR]

High-harmonic generation (HHG) is widely used for up-conversion of amplified (near) infrared ultrafast laser pulses to short wavelengths. We demonstrate that Ramsey-comb spectroscopy, based on two such pulses derived from a frequency-comb laser, enables us to observe phase effects in this process with a few mrad precision. As a result, we could perform the most accurate spectroscopic measurement based on light from HHG, illustrated with a determination of the 5p6 → 5p58s²[3/2]1 transition at 110 nm in 132Xe. We improve its relative accuracy 104 times to a value of 2.3 × 10-10. This is 3.6 times better than shown before involving HHG, and promising to enable 1S - 2S spectroscopy of He+ for fundamental tests. [ABSTRACT FROM AUTHOR]

The ionization energy of ortho-H2 has been determined to be EoI(H2)/(hc)=124 357.238 062(25) cm-1 from measurements of the GK(1,1)-X(0,1) interval by Doppler-free, two-photon spectroscopy using a narrow band 179-nm laser source and the ionization energy of the GK(1,1) state by continuous-wave, near-infrared laser spectroscopy. EoI(H2) was used to derive the dissociation energy of H2, DN=10(H2), at 35 999.582 894(25) cm-1 with a precision that is more than one order of magnitude better than all previous results. The new result challenges calculations of this quantity and represents a benchmark value for future relativistic and QED calculations of molecular energies. [ABSTRACT FROM AUTHOR]

Weak transitions in the (2,0) overtone band of the hydrogen deuteride molecule at λ=1.38 µm were measured in saturated absorption using the technique of noise-immune cavity-enhanced optical heterodyne molecular spectroscopy. Narrow Doppler-free lines were interrogated with a spectroscopy laser locked to a frequency comb laser referenced to an atomic clock to yield transition frequencies [R(1)=217105181895(20) kHz; R(2)=219042856621(28) kHz; R(3)=220704304951(28) kHz] at three orders of magnitude improved accuracy. These benchmark values provide a test of QED in the smallest neutral molecule, and they open up an avenue to resolve the proton radius puzzle, as well as constrain putative fifth forces and extra dimensions. [ABSTRACT FROM AUTHOR]

Molecular hydrogen and its isotopic and ionic species are benchmark systems for testing quantum chemical theory. Advances in molecular energy structure calculations enable the experimental verification of quantum electrodynamics and potentially a determination of the proton charge radius from H2 spectroscopy. We measure the ground state energy in ortho-H2 relative to the first electronically excited state by Ramsey-comb laser spectroscopy on the EF¹Σ+g-X¹Σ+g(0,0) Q1 transition. The resulting transition frequency of 2 971 234 992 965(73) kHz is 2 orders of magnitude more accurate than previous measurements. This paves the way for a considerably improved determination of the dissociation energy (D0) for fundamental tests with molecular hydrogen. [ABSTRACT FROM AUTHOR]

High-precision spectroscopy in systems such as molecular hydrogen and helium ions is very interesting in view of tests of quantum electrodynamics and the proton radius puzzle. However, the required deep ultraviolet and shorter wavelengths pose serious experimental challenges. Here we show Ramsey-comb spectroscopy in the deep ultraviolet for the first time, thereby demonstrating its enabling capabilities for precision spectroscopy at short wavelengths. We excite Kr84 in an atomic beam on the two-photon 4p6→4p55p[1/2]0 transition at 212.55 nm. It is shown that the ac-Stark shift is effectively eliminated, and combined with a counterpropagating excitation geometry to suppress Doppler effects, a transition frequency of 2 820 833 101 679(103) kHz is found. The uncertainty of our measurement is 34 times smaller than the best previous measurement, and only limited by the 27 ns lifetime of the excited state. [ABSTRACT FROM AUTHOR]