Short Infrared Laser Pulses Research Articles

Cell and tissue manipulation with ultrashort infrared laser pulses in light-sheet microscopy

Three-dimensional live imaging has become an indispensable technique in the fields of cell, developmental and neural biology. Precise spatio-temporal manipulation of biological entities is often required for a deeper functional understanding of the underlying biological process. Here we present a home-built integrated framework and optical design that combines three-dimensional light-sheet imaging over time with precise spatio-temporal optical manipulations induced by short infrared laser pulses. We demonstrate their potential for sub-cellular ablation of neurons and nuclei, tissue cauterization and optogenetics by using the Drosophila melanogaster and zebrafish model systems.

Ionization probability of sputtered indium under irradiation with 20-keV fullerene and argon gas cluster projectiles

The formation probability of secondary ions released from a metal surface under bombardment with a 20-keV cluster ion beam is investigated using combined time-of-flight secondary ion and neutral mass spectrometry (Tof-SIMS/SNMS) experiments. The emitted neutral atoms and clusters are post-ionized after their ejection using strong-field photoionization in an intense short infrared laser pulse. Comparing the secondary ion signal with that of the corresponding neutral particles, the ionization probability of sputtered indium atoms and Inn clusters with n = 2–4 is determined. The results are compared between two different projectile cluster ions, namely i) C60+ and ii) Arn+ with n∼1000. It is shown that the ionization probability obtained with the fullerene cluster is by roughly a factor 4 larger than that obtained with the rare gas cluster, thereby indicating that there is no nonlinear enhancement of the transient electronic excitation generated by a cluster impact.

Molecular SIMS Ionization Probability Studied with Laser Postionization: Influence of the Projectile Cluster

The formation probability of (quasi-)molecular secondary ions released from an organic film under bombardment with a 20 keV cluster ion beam is investigated using combined time-of-flight secondary ion and neutral mass spectrometry (ToF-SIMS/SNMS) experiments. The emitted neutral molecules are postionized after their ejection using strong-field photoionization in an intense short infrared laser pulse. Comparing the (quasi)-molecular secondary ion signal with that of the corresponding neutral molecules, the ionization probability of sputtered intact coronene and guanine molecules is determined. The results are compared between two different projectile cluster ions, namely (i) C60+ and (ii) Arn+ with n ∼ 1000. It is shown that both projectiles deliver different SNMS spectra, indicating pronounced differences in the collision-induced fragmentation of the emitted molecules. For guanine, the ionization probability obtained with both projectiles is of the same order of magnitude (∼10–3), with the fullerene cluster producing a slightly larger ionization efficiency than the rare gas cluster. For coronene, on the other hand, a substantially lower ionization efficiency is found for the gas cluster projectile.

Action potential block in neurons by infrared light.

Short infrared laser pulses (SILP) have many physiological effects on cells, including the ability to stimulate action potentials (APs) in neurons. Here, we show that SILPs can also reversibly block APs. Reversible AP block in hippocampal neurons was observed following SILP (0.26 to [Formula: see text]; 1.37 to 5.01ms; 1869nm) with the block persisting for more than 1s with exposures greater than [Formula: see text]. AP block was sustained for 30s with SILPs pulsed at 1 to 7Hz. Full recovery of neuronal activity was observed 5 to 30s post SILP exposure. These results indicate that SILP can be used for noncontact, reversible AP block. Due to the high spatial precision and noncontact manner of infrared light delivery, AP block by SILP (infrared neural inhibition) has the potential to transform medical care for sustained pain inhibition and suppression of unwanted nerve activity.

Laser-assisted electron scattering in strong-field ionization of dense water vapor by ultrashort laser pulses

We report on strong-field ionization of dense water gas in a short infrared laser pulse. By employing a unique combination of photoelectron spectroscopy with a liquid micro-jet technique, we observe how the character of electron emission at high kinetic energies changes with the increase of the medium density. This change is associated with the process of laser-assisted electron scattering (LAES) on neighboring particles, which becomes a dominant mechanism of hot electron emission at higher medium densities. The manifestation of this mechanism is found to require densities that are orders of magnitude lower than those considered for heating the laser-generated plasmas via the LAES process. The experimental results are supported by simulations of the LAES yield with the use of the Kroll–Watson theory.

Population trapping in bound states during IR-assisted ultrafast photoionization ofNe+

We have investigated photoionization of Ne$^+$ in the combined field of a short infra-red laser pulse and a delayed ultra-short pulse of the infra-red laser's 23$^r$$^d$ harmonic. We observe an ionization yield compatible with a picture in which one electron gets excited into Rydberg states by the harmonic laser field and is subsequently removed by the infra-red laser field. Modulations are seen in the ionization yield as a function of time delay. These modulations originate from the trapping of population in low members of the Rydberg series with different states being populated at different ranges of delay times. The calculations further demonstrate that single-threshold calculations cannot reproduce the Ne$^+$ photoionization yields obtained in multi-threshold calculations.

Estudo teórico da estrutura eletrônica e da dinâmica induzida por lasers da molécula de HCl

Potential energy and dipole moment curves for the HCl molecule were computed. Calculations were performed at different levels of theory (DFT, MRCI). Spectroscopic properties are reported and compared with experimental data, for validating the theoretical approaches. Interaction of infrared radiation with HCl is simulated using the wave packet formalism. The quantum control model for population dynamics of the vibrational levels, based on pi-pulse theory, is applied. The results demonstrate that wavepackets with specific composition can be built with short infrared laser pulses and provide the basis for studies of H + HCl collision dynamics with infrared laser excitation.

Ionization of Atoms by Intense Laser Pulses

The process of ionization of a hydrogen atom by a short infrared laser pulse is studied in the regime of very large pulse intensity, in the dipole approximation. Let $A$ denote the integral of the electric field of the pulse over time at the location of the atomic nucleus. It is shown that, in the limit where $|A| \to \infty$, the ionization probability approaches unity and the electron is ejected into a cone opening in the direction of $-A$ and of arbitrarily small opening angle. Asymptotics of various physical quantities in $|A|^{-1}$ is studied carefully. Our results are in qualitative agreement with experimental data reported in \cite{1,2}.

Current corneal femtosecond laser techniques

The technological advances in ophthalmology, and especially those concerning the field of refractive surgery, have led the scientific community to the introduction of lasers with ultra fast pulses. Femtosecond laser function is based on the fact that ultra short infrared laser pulses are precisely focused inside the corneal tissue. At the focal point, tissue is disrupted and a small bubble is created. By placing these bubbles next to each other in a specific pattern, it is possible to create a cut that can have virtually any shape and position. Femtosecond lasers have been developed to decrease the energy necessary to incise tissues and minimize the thermal damage of the surrounding structures. The accuracy, safety and predictability of this new technology is proven every day in clinical practice, and a continuous line of new applications in corneal surgery confirm its efficacy and value.

Vibrationally excited ultrafast thermodynamic phase transitions at the water/air interface

The extraordinary ability of the hydrogen-bond network of water in the condensed phase to thermalize vibrational excitations within several picoseconds, even under supercritical conditions, offers the possibility of creating highly excited thermodynamic states at water surfaces on ultrafast time scales using vibrationally resonant short infrared laser pulses. We experimentally and numerically studied such states created by depositing ~100 ps long pulses tuned to the 3400 cm(-1) O–H stretch vibration at the water/air interface using time-resolved dark-field imaging and time-resolved optical reflectivity. The results are reasonably well described by using a hydrodynamic ablation model under the assumption of impulsive heat deposition. The large thermoelastic stress amplitudes on the order of 1 GPa created within 100 ps by depositing laser pulses with ~1 J cm(-2) fluence were inferred from the numerical simulations. Stresses of this magnitude drive the excited water layer into a very fast expansion resulting in rapid adiabatic cooling and thorough vaporization within a few nanoseconds. The spatial and temporal lengths scales of the ablation plume are nearly ideal for ejecting molecules into the gas phase with minimum perturbation for applications ranging from mass spectrometry and laser surgery to the development of extremely high pressure molecular beams.

Modeling of thermal effects on photo-dissociation dynamics of diatomic molecular ion HCl +

The dynamics of photo-dissociation of a diatomic molecular ion (HCl +) interacting with ultra short infrared laser pulses have been explored at both zero and non-zero temperatures. The potential that we have used for the systems was calibrated with the help of the ab initio theoretical calculation at the CCSD/aug-cc-pVTZ level and then fitted with an appropriate Morse potential. The vibrational eigenvalues and eigenfunctions were obtained by the time-independent Fourier grid Hamiltonian (FGH) method. Then, the time dependent Schrödinger equation is solved by invoking the time dependent FGH method. The changes of photo-dissociation probability of HCl + have been explored with the variation of the light intensity, and temperature. Our model has been introduced to mimic the medium induced perturbation.

X-ray generation by laser-cluster interaction

We investigate the efficient heating of quasi-free electrons during the interaction of short infrared laser pulses with large rare-gas clusters. In the framework of our mean-field classical transport simulation we are able to explain the emission of characteristic x-rays at moderate laser intensities (I ∼ 10 15 Wcm -2 ) where the ponderomotive energy of the electrons is by far to low to allow for the creation of inner-shell vacancies. We identify large-angle elastic electron-ion scattering as an important heating mechanism at moderate laser intensities.

Detailed comparison of theory and experiment of strong-field photodetachment of the negative hydrogen ion

We study the strong-field interaction of a negative hydrogen ion in a short infrared laser pulse. An imaging technique is employed in a fast ion beam to record angular-resolved energy distributions of the photodetached electrons. The spectrum exhibits four excess photon channels. A detailed analysis of the energy and angular distribution is presented, including a comparison with recent theories. From our data we determine elastic-scattering phase shifts of the partial continuum waves in the lowest-order detachment channel. Quantitative agreement with scattering theory is obtained. A quantum interference effect predicted in a recent Keldysh-like theory is observed at energies close to threshold. We propose an analogy to a double-slit model which explains the interference features in a simple and intuitive way. We also verify the applicability of the Wigner threshold law in the strong-field regime and discuss its role in the observed quantum interference.

Photodetachment of H- in a strong infrared laser field.

Negative hydrogen ions are exposed to a short infrared laser pulse of 2.15 microm wavelength and 250 fs duration. An imaging technique is used to record the energy resolved angular distribution of photoelectrons. The energy spectrum reveals at least three excess photon detachment channels. A quantum interference effect, resulting in an unusual dependence of the angular distribution on the electron kinetic energy, is most prominent in the lowest two-photon detachment channel. The appearance of this effect is discussed in terms of the threshold law of photodetachment.

Picosecond laser control of bond-selective dissociation and clockwise and anticlockwise rotation of the dissociation fragments: applications to a three-dimensional model of HONO 2 in the ground electronic state

Quantum dynamical simulations within the Schrödinger wave-function formalism have been performed for a three-dimensional (3-D) model of HONO 2 in the ground electronic state excited by linearly polarized shaped infrared (IR) laser pulses of picosecond (ps) and subpicosecond duration. The OH and the ON single bond stretches are explicitly treated together with the bending angle between them on the basis of the respective, ab initio defined, 3-D potential-energy surface and dipole function. Selective breaking of the ON single bond by optimally shaped IR laser pulses with more than 97% probability is demonstrated. Selective preparation of the clockwise and anticlockwise rotating OH fragments after the breakage of the ON single bond in HONO 2 by optimally designed subpicosecond IR laser pulses is demonstrated as well, with the respective branching ratio ranging from about 2.35 to 7.04. It is also demonstrated that optimally designed strong and short IR laser pulses can compete against intramolecular vibrational-enegry redistribution (IVR) and prepare a desirable molecular state.

Effect of Rotations and Shape Resonances on Photoassociation and Photoacceleration by Short Infrared Laser Pulses

A quantum dynamical description of an atomic collision pair interacting with the electric field of a short infrared laser pulse is developed. Inelastic processes in the electronic ground state are due to stimulated emission resulting in photoassociation, or absorption leading to photoacceleration. A perturbative approach based on a state space representation is compared with a numerical treatment using a grid representation in coordinate space. Special emphasis is on the role of rotations and, in particular, of shape resonances. It is shown that these quasibound states which are supported by the centrifugal barrier (for J> 0) can be used as initial states to effectively populate a selected bound state with specific vibrational and rotational quantum number (photoassociation), or a partial wave of a scattering state with defined energy and rotational quantum number (photoacceleration). Simulations are carried out for the prototype H + Cl collision pair. Also the effect of averaging over initial conditions (velocity, angular momenta) is investigated for a supersonic beam experiment. For a narrow velocity distribution, we predict the presence of a resonance structure of the association and acceleration probability as a function of the mean collision energy.

A fast infrared detector based on patterned YBCO thin film

Detectors for infrared radiation ( lambda =0.85 mu m) were made of 50 nm thick YBa2Cu3O7- delta films on LaAlO3 and MgO or 60 nm thick films on NdGaO3. Parallel strips (1 mu m wide by 20 mu m long) were patterned in the films and formed the active device. These devices were designed to detect short infrared laser pulses by electron heating. The detectors were current biased into the resistive and the normal states. The response was studied in direct pulse measurements as well as by amplitude modulation of a laser. The pulse measurements showed a fast picosecond response followed by a slower decay related to phonon escape through the film-substrate interface and heat diffusion in the substrate. The frequency spectra up to 10 GHz showed two slopes with a knee corresponding to the phonon escape time.

Mid-infrared nonlinear phenomena in polycrystalline semiconductors

We have studied second-harmonic generation by 30 ps and 70 ns 10 μm CO2 laser pulses in nonlinear polycrystalline ZnSe, CdTe and GaAs samples. Second-harmonic generation in these materials can limit the amplification of high-power CO2-laser pulses in amplifier chains sealed with these polycrystalline IR-transmission materials. On the other hand, we now demonstrate for the first time that these materials are suited as nonliner elements for autocorrelation measurements on short infrared laser pulses. For such pulse-width measurements polycrystalline materials have an advantage over single crystals, e.g. GaAs, because they are insensitive to misalignement. Furthermore, these polycrystalline optical elements are easier and cheaper to manufacture than single crystal devices. With such polycrystalline materials we were able to realize reliable autocorrelation measurements of 30–300 ps 10 μm optical-free-induction-decay (OFID) laser pulses.

Pyroelectric voltage response to short infrared laser pulses in triglycine sulphate and strontium-barium niobate

Analysis is given of the voltage response in a pyroelectric sample to ir signals much shorter than the electronic and thermal time constants of the sample. The equation of the response is derived, and the dependence of the various parameters of the response on the frequency and energy of the pulses as well as on the parameters of the sample and on material constants is compared with experiment in triglycine sulphate and strontium-barium niobate. The peak value of the response is found to be independent of the load resistance as well as of the pulse frequency, and proportional to the energy of the signals, provided that the mean temperature of the sample is far enough from the Curie point.

Peak Voltage of the Pyroelectric Response to Short Infrared Laser Pulses

The peak voltage of the response in a pyroelectric sample to ir signals much shorter than the thermal and electronic time constants of the sample is shown to be proportional to the energy absorbed per signal, and independent of load resistance and signal repetition frequency, as long as temperature is far enough from the Curie point. These results were checked experimentally in triglycine sulphate and strontium-barium niobate.