W. Hogervorst

A source of 2 terawatt, 2.7 cycle laser pulses based on noncollinear optical parametric chirped pulse amplification

We demonstrate a noncollinear optical parametric chirped pulse amplifier system that produces 7.6 fs pulses with a peak power of 2 terawatt at 30 Hz repetition rate. Using an ultra-broadband Ti:Sapphire seed oscillator and grating-based stretching and compression combined with an LCD phase-shaper, we amplify a 310 nm wide spectrum with a total gain of 3x10(7), and compress it within 5% of its Fourier limit. The total integrated parametric fluorescence is kept below 0.2%, leading to a pre-pulse contrast of 2 x10(-8) on picosecond timescales.

Generation of few-cycle terawatt light pulses using optical parametric chirped pulse amplification

We demonstrate the generation of 9.8+/-0.3 fs laser pulses with a peak power exceeding one terawatt at 30 Hz repetition rate, using optical parametric chirped pulse amplification. The amplifier is pumped by 140 mJ, 60 ps pulses at 532 nm, and amplifies seed pulses from a Ti:Sapphire oscillator to 23 mJ/pulse, resulting in 10.5 mJ/pulse after compression while amplified fluorescence is kept below 1%. We employ grating-based stretching and compression in combination with an LCD phase-shaper, allowing compression close to the Fourier limit of 9.3 fs.

Efficient temporal compression of coherent nanosecond pulses in a compact SBS generator-amplifier setup

A pulse compressor based on stimulated Brillouin scattering (SBS) in liquids is experimentally and theoretically investigated. It allows for the compression of Fourier-transform limited nanosecond pulses of several hundreds of millijoules of energy with both high conversion efficiency and a high temporal compression factor. The two-cell generator-amplifier arrangement is of a compact design not requiring external attenuation of the generator cell input energy. Pulses from an injection-seeded, frequency-doubled Nd:YAG laser of 300-mJ energy were compressed by a factor variable between 6 and 21 at up to 75% reflectivity. Deviation from unity SBS reflectivity is predominantly determined by optical component losses. The generation of 270-ps pulses with high beam quality was achieved in liquid methanol. These powerful pulses of variable duration are difficult to produce with common laser systems and are highly suited for the generation of high-harmonics in gases.

High-power parametric amplification of 11.8-fs laser pulses with carrier-envelope phase control

Phase-stable parametric chirped-pulse amplification of ultrashort pulses from a carrier-envelope phase-stabilized mode-locked Ti:sapphire oscillator (11.0 fs) to 0.25 mJ/pulse at 1 kHz is demonstrated. Compression with a grating compressor and a LCD shaper yields near-Fourier-limited 11.8-fs pulses with an energy of 0.12 mJ. The amplifier is pumped by 532-nm pulses from a synchronized mode-locked laser, Nd:YAG amplifier system. This approach is shown to be promising for the next generation of ultrafast amplifiers aimed at producing terawatt-level phase-controlled few-cycle laser pulses.

PRECISION VUV SPECTROSCOPY OF AR I AT 105 NM

The results of a precision measurement of the 3p 6 -3p 5 4s 0 1 1 (1s2 in Paschen notation) transition in argon by resonance-enhanced 1 VUV + 1 UV photo-ionization spectroscopy at 105 nm are presented. Tunable narrow-band VUV radiation is generated by frequency up- conversion of the powerful output of a pulsed dye amplifier system. A transition frequency of 95 399:833.3/ cm 1 in 40 Ar is measured, in agreement with (but an order of magnitude more accurate than) the existing value for this transition. Transition isotope shifts 40 38 D 550.10/ MHz and 40 36 D 1036.7/ MHz are obtained, from which specific mass shifts are deduced. An improved value for the ionization potential in argon (IPD 127 109:842.4/ cm 1 )i s also given. Over the past decade, with the development of powerful dye amplifiers and harmonic- generation techniques, the vacuum ultraviolet (VUV) spectral region became accessible with narrow-band tunable laser sources, thus making possible spectroscopic studies of transitions involving ground states of noble gas atoms with unsurpassed accuracy. The energy level structure of the noble gases is such that the entire manifold of electronically excited states is separated from the electronic ground state by a large energy gap. A laser at 58 nm was used (1) to bridge this gap in helium, resulting in accurate values for the ionization potential (IP), the ground state Lamb shift and the 3 He- 4 He isotope shift. Similar studies of heavier rare gases such as Ne and Kr in the VUV (2, 3) gave valuable information on the level structure of these more complex systems and at present an accuracy of 0:005 cm 1 has been reached for some VUV transitions. However, in Ar accurate values for the VUV transition frequencies are missing; hence the ionization potential is not known accurately for this atom. Recently (4), a multichannel quantum defect analysis of the Rydberg series of 40 Ar was reported, determining accurate values (0:003 cm 1 ) for the two ionization potentials jcD 1 ; 3 with respect to the metastable 3 P2 level (1s5 in Paschen notation), populated in a discharge. In this letter we report on a precise calibration of the 3p 6 . 1 S0/-3p 5 4s 0 1 1 .1s2/ transition in argon by 1VUV+1UV photo-ionization using a narrow-band laser source at 105 nm. The accuracy of 0:003 cm 1 is a factor of 15 better than the best known value of 0:05 cm 1 (5) dating from the early 1970s. Furthermore, an analysis of the isotope shifts in the 1 S0-1s2 transition for the three stable argon isotopes (36, 38, 40) is made. In general, these shifts are due to differences in the nuclear mass (mass shifts) and nuclear charge distribution (field shifts). To a good approximation (6) the isotope shift can be presented as a sum of the mass and field shift. The latter is negligible for light elements such as argon, but it can dominate the isotope shift in heavy elements. The mass shift can be described as consisting of two parts:

Predissociation rates in carbon monoxide: dependence on rotational state, parity and isotope

Abstract A high-resolution spectroscopic study of carbon monoxide has been performed using a narrow-band and tunable extreme-ultraviolet laser source in the wavelength range 91–97 nm. For three isotopes 12 C 16 , 13 C 16 O and 13 C 18 O the (4pπ)L 1 Π, ν=0, (4 p σ)K 1 Σ + , ν=0 and (3sσ)W 1 Π, ν=0 states were investigated. The 1 Π, ν=2, (3 s σ)W 1 Π, ν=2 and (3dπ)L′ 1 Π, ν=1 states were studied for 12 C 16 and 13 C 16 O. The 1 Π, ν=0 state at 109564.58 cm −1 , the (6pσ) 1 Σ + , ν=0 state at 109173.68 cm −1 , the (5pσ) 1 Σ + , ν=0 state at 107174.44 cm −1 , and the (4dσ) 1 Σ + , ν=0 state at 105676.30 cm −1 were excited only for the main isotope 16 C 16 O. Previously unknwon states are found at 107365.87 cm −1 ( 1 Σ + ) for 12 C 16 O and at 103203.07 cm −1 ( 1 Π) for 13 C 18 O. Indirect evidence is found for a perturber state at 107708±2 cm −2 cm −1 for 12 C 16 O, while spectroscopic information on the E 1 Π, ν=5 state of 13 C 18 O is deduced from a deperturbation analysis. A rotational-state and isotope-dependent predissociation rate is found for almost all states. A parity dependence is observed for the (4pπ)L 1 Π, ν=0 and (3sσ)W 1 Π, ν=0 states, where the predissociation rate of the Π e component varies proportional to J ( J +1). This effect is attributed a coupling with the repulsive part of the D′ 1 Σ + state. Several examples of accidental predissociations have been found, particularly in the (4dσ) 1 Σ + , ν=0 state.

Quantitative analysis of decay transients applied to a multi-mode pulsed cavity ring-down experiment.

The intensity and noise properties of decay transients obtained in a generic pulsed cavity ringdown experiment are analyzed experimentally and theoretically. A weighted nonlinear least-squares analysis of digitized decay transients is shown that avoids baseline offset effects that induce systematic deviations in the estimation of decay rates. As follows from simulations not only is it a method that provides correct estimates for the values of the fit parameters, but moreover it also yields a correct estimate of the precision of the fit parameters. It is shown experimentally that a properly aligned stable optical resonator can effectively yield monoexponential decays under multimode excitation. An on-line method has been developed, based on a statistical analysis of the noise properties of the decay transients, to align a stable resonator toward this monoexponential decay.

Accidental predissociation phenomena in the E(1)Pi, v=0 and v=1 states of (CO)-C-12-O-16 and (CO)-C-13-O-16

We have studied v=0 and v=1 levels of the E 1Π state of CO in excitation from the ground state by one‐ and two‐photon transitions, thus probing e and f Λ‐doublet components. New accidental predissociations were found in the E 1Π, v=0 state for high J values (Je=41, 44 for 12C16O and Je=41, 50 for 13C16O). The predissociation phenomenon in the E 1Π, v=1 state at J=7 was reinvestigated and for both e and f components also J=9, 10, and 12 were found to be perturbed. Perturbations by all three spin components of a k 3Π, v=5 state were deduced. Furthermore the accidental predissociation in E 1Π, v=0 Je=31 was reinvestigated. Measurements of spectral line shifts were modeled assuming a spin‐orbit coupling between E 1Π and the 3Π1 component of the k 3Π state. Relative predissociation lifetimes of k 3Π, v=3 and 5 with respect to E 1Π, v=0 and v=1 are deduced from an analysis of observed intensity effects. For the E 1Π, v=1 state rotational state dependent lifetimes were determined at low‐J values. Line positions ...

RADIATIVE AND COLLISIONAL RELAXATION OF A SINGLE ROVIBRATIONAL QUANTUM STATE OF I2-E(0(G)(+)), UPSILON = 8, J = 56

Abstract Dispersed fluorescence from a single quantum state in I2 is studied. The E(0+g), v=8, J=56 state is excited via two-colour absorption employing nanosecond lasers. Direct fluorescence in the range 390–455 nm is compared with Franck-Condon calculations for discrete transitions in the E(0+g)-B3Π(0+u) system. A Franck-Condon diffraction pattern in the range 355-375 nm is attributed to the newly identified E(0+g-1Π(1u) system. State-specific inelastic collision processes E(0+g-D(0+u) are observed and secondary fluorescence in the D(0+u)-X(0+g) system in the range 300–330 nm is analyzed.

Degenerate Bose-Fermi mixture of metastable atoms

We report the observation of simultaneous quantum degeneracy in a dilute gaseous Bose-Fermi mixture of metastable atoms. Sympathetic cooling of helium-3 (fermion) by helium-4 (boson), both in the lowest triplet state, allows us to produce ensembles containing more than 10(6) atoms of each isotope at temperatures below 1 microK, and achieve a fermionic degeneracy parameter of T/TF = 0.45. Because of their high internal energy, the detection of individual metastable atoms with subnanosecond time resolution is possible, permitting the study of bosonic and fermionic quantum gases with unprecedented precision. This may lead to metastable helium becoming the mainstay of quantum atom optics.