High Repetition Rate Ti Research Articles

The Role of Thermal Accumulation on the Fabrication of Diffraction Gratings in Ophthalmic PHEMA by Ultrashort Laser Direct Writing.

The fabrication of diffraction gratings by ultrashort direct laser writing in poly-hydroxyethyl-methacrylate (PHEMA) polymers used as soft contact lenses is reported. Diffraction gratings were inscribed by focusing laser radiation 100 µm underneath the surface of the samples. Low- and high-repetition rate Ti:sapphire lasers with 120 fs pulsewidth working at 1 kHz and 80 MHz respectively were used to assess the role of thermal accumulation on microstructural and optical characteristics. Periodic patterns were produced for different values of repetition rate, pulse energy, laser wavelength, distance between tracks, and scanning speed. Compositional and structural modifications of the processed areas were studied by micro-Raman spectroscopy showing that under certain parameters, thermal accumulation may result in local densification. Far-field diffraction patterns were recorded for the produced gratings to assess the refractive index change induced in the processed areas.

High-resolution in-source laser spectroscopy in perpendicular geometry

Operation of the novel laser ion source unit LIST (Laser Ion Source and Trap), operating at the on-line radioactive ion beam facility ISOLDE at CERN allowed for the production of ultra-pure beams of exotic isotopes far-off stability as well as direct isobar-free laser spectroscopy, giving access to the study of atomic and nuclear properties of so far inaccessible nuclides. We present a specific upgrade and adaption of the LIST targeted for high resolution spectroscopy with a Doppler-reduced perpendicular atom - laser beam geometry. With this PI-LIST (Perpendicularly Illuminated Laser Ion Source and Trap) setup, experimental linewidths below 100 MHz could be demonstrated in optical laser spectroscopy off-line, applying a pulsed injection-locked high repetition rate Ti:sapphire laser. A dual repeller configuration ensured highest suppression of isobaric interferences and almost background-free measurements on small samples in the order of 1011 atoms.

High efficiency resonance ionization of palladium with Ti:sapphire lasers

This work presents the development and testing of highly efficient excitation schemes for resonance ionization of palladium. To achieve the highest ionization efficiencies, a high-power, high repetition rate Ti:sapphire laser system was used and 2-step, 3-step and 4-step schemes were investigated and compared. Starting from different excited steps, the frequencies of the final ionization steps were tuned across the full accessible spectral range of the laser system, revealing several autoionizing Rydberg series, which converge towards the energetically higher lying state of the Pd+ ion ground state configuration. Through proper choice of these excitation steps, we developed a highly efficient, fully resonant 3-step excitation scheme, which lead to overall efficiencies of % and %, measured at two independent mass separator setups. To our knowledge, these are presently the highest efficiency values ever achieved with a resonance ionization laser ion source.

Performance of a high repetition pulse rate laser system for in-gas-jet laser ionization studies with the Leuven laser ion source @ LISOL

The laser ionization efficiency of the Leuven gas cell-based laser ion source was investigated under on- and off-line conditions using two distinctly different laser setups: a low-repetition rate dye laser system and a high-repetition rate Ti:sapphire laser system. A systematic study of the ion signal dependence on repetition rate and laser pulse energy was performed in off-line tests using stable cobalt and copper isotopes. These studies also included in-gas-jet laser spectroscopy measurements on the hyperfine structure of 63Cu. A final run under on-line conditions in which the radioactive isotope 59Cu (T1/2=81.5s) was produced, showed a comparable yield of the two laser systems for in-gas-cell ionization. However, a significantly improved time overlap by using the high-repetition rate laser system for in-gas-jet ionization was demonstrated by an increase of the overall duty cycle, and at the same time, pointed to the need for a better shaped atomic jet to reach higher ionization efficiencies.

Suppression of parasitic lasing in high energy, high repetition rate Ti:sapphire laser amplifiers

Transverse parasitic lasing is well known for limiting the signal gain and the pulse energy that can be extracted from Ti:sapphire petawatt amplifiers. We have developed a technique for suppressing these parasitic lasing modes based on perfect refractive index-matching liquid doped with a broad-bandwidth absorber to suppress the transverse lasing while ensuring proper heat removal from the Ti:sapphire crystal. The 800 nm laser output with a bandwidth of 41 nm (FWHM) and peak energy of 22.7 J at a repetition rate of 1 Hz is demonstrated.

Quantum path signatures in harmonic spectra from metal plasma

We have observed the signatures of quantum trajectories while generating harmonics in metal plasmas by using a high pulse repetition rate (1-kHz) Ti:sapphire laser source. We present how focusing conditions, laser intensity, plasma concentration, and the chirp of laser radiation influence the observation of separated quantum paths. Our studies demonstrate the clear fingerprints of the separated quantum paths in the case of an ionized medium.

Development of laser ablation assisted resonant ionization mass spectrometry for isotope analysis

Stable isotope analysis using Laser Ablation Assisted Resonant Ionization Mass Spectrometry (LA-RIMS) is discussed. For the case of the 87Sr/86Sr isotope ratio measurements with a single color two-photon excitation scheme, the mass discrimination effects, which occur in LA-RIMS, are analyzed and a precision of 0.6% was extracted. For preparation of LA-RIMS on Hf isotopes, a novel two-color resonant excitation scheme with subsequent non-resonant ionization has been established using a high repetition-rate Ti:Sapphire laser system.

Development of femtosecond X-ray source in helium atmosphere with millijoule high-repetition-rate femtosecond laser

High intensity Cu Kα X-ray was generated in helium at atmospheric pressure (760 torr) using a commercial millijoule high-repetition rate Ti: sapphire laser. The characteristic Kα X-ray was generated by focusing the 0.06 mJ－1.46 mJ, 100 fs and 1 kHz repetition femtosecond laser onto a solid Cu target to a spot with a 5 μm diameter. We obtained the characteristic Kα X-ray of 5.4 × 109 photos/s into 2π sr at a 1 kHz repetition rate with 5.0 × 10-6 conversion efficiency. Kα X-ray intensity can be enhanced with 4－8% prepulse plasma into 7.7 × 109 photos/s/sr with 6.8 × 10-6 conversion efficiency. The X-ray intensity and conversion efficiency in helium achieved the almost the same level as in vacuum. Such vacuum-free femtosecond X-ray source with a tabletop laser can be a promising and easy accessible tool for time-resolved X-ray diffraction and other radiographic applications. The time-resolved X-ray diffraction experiment would reveal the ultrafast dynamics in crystalline materials, such as coherent phonon vibrations and ultrafast phase transitions.

An injection-seeded high-repetition rate Ti:Sapphire laser for high-resolution spectroscopy and trace analysis of rare isotopes

An injection-seeded high-repetition rate (∼10 kHz) Ti:sapphire laser with a spectral bandwidth of ∼20 MHz and an average output power of above 1.5 W has been developed. We report on its demonstration and characteristics with respect to the spectral, temporal, and spatial properties as well as the output energy. In crossed-beam resonance ionization on a well-collimated thermal atomic beam, the ∼200 MHz hyperfine structure of the D2 transition at 308 nm of 27Al has been well resolved. Applications of the system in the field of insource laser spectroscopy for on-line produced short-lived radioactive isotopes as well as for selective-trace isotope determination are discussed.

Design and demonstration of a high-energy booster amplifier for a high-repetition rate petawatt class laser system

We have successfully developed a high-energy, high-repetition rate Ti:sapphire laser system that delivers 33 J before compression at 0.1 Hz. The final booster amplifier is based on a 100 mm diameter Ti:sapphire crystal pumped with 72 J of energy in six beams delivered by three frequency-doubled high-repetition rate Nd:glass lasers. This system is, to the best of our knowledge, the first demonstrated petawatt class laser system running at a high repetition rate.

Adaptive wavefront correction on a 100-TW/10-Hz chirped pulse amplification laser and effect of residual wavefront on beam propagation

We demonstrate the wavefront correction of a 100-TW (25 fs, 2.5 J) high repetition rate Ti:sapphire laser. A 36-actuator bimorph deformable mirror was used under vacuum and the adaptive optic system is working at 10 Hz in a closed-loop configuration with a Shack–Hartmann wavefront sensor. We also numerically studied the effects of the deformable mirror actuators on laser beam free propagation to determine the ideal position of the deformable mirror in the laser chain. Our ability to focus the beam was improved to near-diffraction-limited quality and intensity as high as 1.4 × 10 20 W/cm 2 was reached with a 500-mm focal length off-axis parabolic mirror.

Resonance in the 1π photoemission cross-section of CO on Pt( [formula omitted]) measured by high harmonic radiation

Femtosecond pulses of a table-top, high-repetition rate (1 kHz) Ti:sapphire laser system are focussed into rare gases to produce high harmonic radiation in the range of 60–11 nm ( hν=20–120 eV). The c(4×2)-2CO-covered Pt(1 1 1) surface is investigated by angle resolved photoelectron spectroscopy using this radiation. Both the coarse tunability in steps of 3.1 eV as well as a fine tuning within a single harmonic are utilized in the measurements. The photoemission cross-section of CO induced structures, in particular the CO 1π orbital, is investigated. For this state a narrow resonance is observed, which has not been reported so far. A resonant excitation of electrons from the occupied 3σ level into the unoccupied 2π level followed by the autoionization of the 1π CO state or Auger decay is proposed to cause this resonance.

Gamma-neutron activation experiments using laser wakefield accelerators

Gamma-neutron activation experiments have been performed with relativistic electron beams produced by a laser wakefield accelerator. The electron beams were produced by tightly focusing (spot diameter ≈6 μm) a high power (up to 10 TW), ultra-short (⩾50 fs) laser beam from a high repetition rate (10 Hz) Ti:sapphire (0.8 μm) laser system, onto a high density (>1019 cm−3) pulsed gasjet of length ≈1.5 mm. Nuclear activation measurements in lead and copper targets indicate the production of electrons with energy in excess of 25 MeV. This result was confirmed by electron distribution measurements using a bending magnet spectrometer. Measured γ-ray and neutron yields are also found to be in reasonable agreement with simulations using a Monte Carlo transport code.

Ion beam induced desorption with postionization using high repetition femtosecond lasers

Static SIMS has shown itself to be a powerful tool for surface analysis with high chemical specificity. Because of the destructive nature of the sputtering process, high spatial resolution analysis (sub-200-nm regime) requires very high yields of emitted ions since there is a very limited amount of material in each image pixel. Generally the sputtered neutral yield is significantly greater than the secondary ion yield. To attain the high sensitivities required it is therefore critical that the ejected neutrals be ionized efficiently with minimal fragmentation. This paper explores the application of a high repetition rate Ti:sapphire based femtosecond laser to the ionization of sputtered and gas phase species from a variety of representative materials including silver, indium, tryptophan, benzo[ a]pyrene, p-nitroaniline and polystyrene. The effects of photon wavelength (800, 400, and 266 nm) and power density on ionization and molecular fragmentation have been studied.