Near-infrared Beam Research Articles

Terahertz dynamics of photogenerated carriers in ferromagnetic InGaMnAs

We have measured the picosecond transient carrier response of InGaMnAs/InP by two-color pump–probe spectroscopy, using an intense near-infrared beam as the pump and a 52.5 μm (5.7 THz) beam as the probe. We observed strongly nonexponential decays, especially at high pump fluences and low temperatures, where a pronounced dip developed in the terahertz differential transmission. This dip disappeared at the highest fluence where a transmission plateau versus time delay was observed. Our band structure calculations suggest that this intriguing behavior may be due to carrier dynamics associated with Γ–L intervalley scattering that becomes efficient when ferromagnetism modifies the band structure.

Tunable room temperature second harmonic generation in glasses doped with CuCl nanocrystalline quantum dots

Two-photon excited emission centered at 379–426 nm in photodarkening borosilicate glass doped with CuCl nanocrystalline quantum dots at room temperature has been observed. The emission is detected in the direction of the fundamental near-infrared beam. Time- and frequency-resolved measurements at room temperature and 77 K indicate that the emission is largely coherent light characteristic of second harmonic generation (SHG). An average conversion efficiency of ∼10 −10 is obtained for a 2 mm thick sample. The observed SHG can originate in the individual noncentrosymmetric nanocrystals, leading to a bulk-like contribution, and at the nanocrystal-glass interface, leading to a surface contribution. The bulk-like conversion efficiency is estimated using previously reported values of coherence length ( 5 μm ) and bulk nonlinear susceptibility. This bulk-like conversion efficiency estimate is found to be smaller than the measured value, suggesting a more prominent surface contribution.

Influence of linearly polarized near-infrared irradiation on deformability of human stored erythrocytes.

To investigate the influence of linearly polarized near-infrared irradiation using the Super Lizer trade mark on deformability of human erythrocytes. Not only low-powered laser but also linearly polarized near-infrared beams have some biostimulation effects on various tissues. There were some reports of erythrocyte deformability improved by low-powered He-Ne laser irradiation. Human erythrocyte samples stored for three weeks were adjusted to 30% hematocrit. Erythrocyte deformability presented as the filter filtration rate was measured. There was no difference of the filter filtration rate between control group without irradiation and the group of 125 mJ/cm(2) exposure level at a wavelength of 830 nm. However, the groups of 625 and 1,250 mJ/cm(2) exposure levels at a wavelength of 830 nm showed higher filter filtration rates compared to the control group. Linearly polarized near-infrared irradiation in a range of 625-1,250 mJ/cm(2) exposure level at a wavelength of 830 nm improved deformability of human stored erythrocytes.

Interferometry with the Large Binocular Telescope

The Large Binocular Telescope (LBT) will be the largest single telescope in the world when it is completed in 2005. The unique structure of the telescope incorporates two, 8.4 meter diameter primary mirrors on a 14.4 meter center-to-center mounting. This configuration provides the equivalent collecting area of a 12 meter telescope, and when combined coherently, the two optical paths offer very interesting possibilities for interferometry. Two initial interferometric instruments are planned for the LBT. A group based at the University of Arizona is constructing LBTI, a pupil-plane, nulling beam combiner operating in the thermal infrared N band. This instrument will search for and measure zodiacal light in candidate stellar systems for the Terrestrial Planet Finder (TPF) and Darwin missions. Expansion ports can accomodate additional instruments. A second group, based in Heidelberg, Arcetri, and Koln, is building LINC-NIRVANA, a near-infrared Fizeau-mode beam combiner. This type of observation preserves phase information and allows true imagery over a wide field of view. Using state-of-the-art detector arrays, coupled with advanced adaptive optics, LINC-NIRVANA will deliver the sensitivity of a 12 m telescope and the spatial resolution of a 23 m telescope, over a field of view up to 2 arc minutes square.

High-pressure bridgman grown CdZnTe for electro-optic applications

The linear electro-optic response of high pressure Bridgman growth semi-insulating Cd0.9Zn0.1Te bulk samples has been characterized. Measurements have been performed in the third optical window for telecommunications around = 1.5 m. The dependence of the Pockels figure of merit on the modulation frequency and on the intensity of the optical probe beam is presented and discussed. Despite the residual optical absorption, Cd0.9Zn0.1Te is not affected by photo-generated auto-inhibition of the Pockels effect. This can be attributed to the action of an efficient intragap recombination center. It is, therefore, a suitable basic material for electro-optic switching of near-infrared beams at low frequency and quasi-continuous wave (cw) regimes. The implementation of a Cd0.9Zn0.1Te-based cross-bar switch for optical communication applications is also presented, which reaches −30 dB of extinction ratio and sub millisecond response time.

First-order coherent THz optical sideband generation from asymmetric QW intersubband transitions

We have generated terahertz (THz) optical sidebands on a near-infrared probe beam by driving an excitonic intersubband resonance with THz electric fields. We use THz radiation polarized along the non-centro-symmetric axis of a quantum well system to generate a comb of sidebands ω sideband= ω NIR+ nω THz. In exploring the rich polarization of the process's power, and NIR frequency dependences we encounter both an efficient perturbative regime modeled by a X (2) non-linear susceptibility, and a non-perturbative regime which has not been previously explored in driven quantum systems.

Odd terahertz optical sidebands from asymmetric excitonic intersubband excitation

We have generated terahertz (THz) optical sidebands on a near-infrared probe beam by driving an excitonic intersubband resonance with THz electric fields. We use THz radiation polarized along the non-centrosymmetric axis of a quantum well system to generate a comb of sidebands ω sideband= ω NIR+ nω THz. In exploring the process's rich polarization, power, and NIR frequency dependences we encounter both an efficient perturbative regime modeled by a χ (2) non-linear susceptibility, and a non-perturbative regime which has not been previously explored in driven quantum systems.

Generation of first-order terahertz optical sidebands in asymmetric coupled quantum wells

We have generated first-order tetrahertz (THz) optical sidebands on a near-infrared (NIR) probe beam by driving an excitonic intersubband resonance with THz electric fields. We use THz radiation polarized along the noncentrosymmetric axis of a quantum well system to generate a comb of sidebands ωsideband=ωNIR+nωTHz. The n=1 process offers an efficient means of modulating a NIR carrier beam at THz frequencies and yields new spectroscopic information on excitonic intersubband transitions.

Imaging individual molecules by two-photon excitation

Abstract Wide-field epi-illumination of supported lipid membranes by a femtosecond near-infrared laser allowed us to identify and follow individual fluorescence labeled lipids in their motion within the membrane. The fluorophores were excited by two-photon absorption of the near-infrared beam as seen from a quadratic dependence of the fluorescence signal on the illumination intensity. The largely decreased background signal on two-photon excitation compared to that using one-photon excitation suggests that single-molecule imaging on native cell membranes will come into reach.

Ion/molecule reactions, mass spectrometry and optical spectroscopy in a linear ion trap

A linear-geometry, radio-frequency, quadrupole ion trap has been developed to generate, purify, accumulate and study atomic and molecular ions in the gas phase. By employing a trap-based system, both reactant and product ions can be stored for significant time periods, which can both enhance the efficiency of gas-phase reaction processes and create an environment to observe collision products after vibrational and rotational excitations have had time to relax. Relaxation occurs via viscous cooling with a dilute buffer gas or via laser cooling. Furthermore, the setup is particularly useful for performing optical spectroscopy on the trapped ions. Atomic and molecular ovens are used to generate thermal beams of neutral species, which are then ionized by electron bombardment. The ions can be trapped, or they can be collided with neutral molecules (e.g. C 60) under well defined experimental conditions. The collision energies are variable over a range from nearly 0 to 200 eV. This feature makes possible studies of complex formation, charge transfer and collision-induced fragmentation as a function of kinetic energy. A wide range of masses of up to 4000 u can be stored and manipulated with this apparatus. Two mass spectrometric techniques for the analysis of trapped ionic species are presented. In one method, parametric excitation of the secular motion is used to generate mass spectra with resolutions as high as 1 part in 800 with a simple experimental setup. The second method is capable of quickly generating mass spectra over the entire range of trapped masses, but has only moderate resolution. These spectra are generated by linearly sweeping the rf-trapping voltage to zero and detecting ions as their trap depth falls below a threshold value. In the trapping volume, which is 10 cm in length and 200 μm in diameter, 10 6 ions can be loaded and stored, corresponding to an ion density above 10 8 cm −3. Such densities facilitate spectroscopy of the stored ions. Both laser-induced fluorescence and photodissociation measurements have been carried out with a cw laser system providing near-infrared, visible, and ultraviolet beams. Absolute, total cross-sections and branching ratios of the photodissociation of MgC + 60 have been measured.

The lowest-frequency bending mode (ν 71) of HCN-HF from near-infrared laser spectroscopy

The lowest intermolecular bending frequency of HCN-HF has been determined in both the ground (73.583(3) cm −1) and excited (73.176(3) cm −1) CH vibrational states using near-infrared laser molecular beam spectroscopy. The results also show that the vibrational predissociation lifetime is weakly dependent on the intermolecular bending state.

Ultracold Ordered Electron Beam

We have started an experimental program to develop an ultracold electron beam, which can be used together with a standard electron cooling device in the Heidelberg Test Storage Ring TSR. In contrast to the standard-type design using electron beam extraction from a heated cathode, the ultracold beam is produced by photoemission of electrons from a cooled semiconductor crystal irradiated with an intense near-infrared laser light beam. Adiabatic acceleration is expected to provide ordering of the electron beam itself. Besides the cooling of ion beams to extremely low temperatures, with the aim of obtaining crystallization, the ultracold beam will constitute an excellent target for atomic physics experiments.

Simple Devices for Measurements of Feeding and Drinking Behavior in Chickens

For the measurement of feeding behaviour in chickens, a simple method was devised using a combination of a near-infrared beam switch, a digital clock, an on-delayed timer and a counter. For the measurement of drinking behaviour, a new method was devised using a capacity-relay, an off-delayed timer, a digital clock and a counter. These devices have proved to be effective for the measurement of feeding and drinking behaviour.

Infrared Transmittance and Kerr Effect of Nitrobenzene

The infrared transmittance of nitrobenzene has been measured for wavelengths between 0.7 and 12 μ for seven samples ranging in thickness from 2 cm to about 10 μ. Other published information has been used to extend these transmittance spectra to 25 μ. These over-all data are presented as an absorption-coefficient spectrum from 0.7 to 25 μ. In addition, this absorption-coefficient spectrum has been analyzed in terms of Kerr-coefficient information which may be extrapolated from visible and near-infrared data. It is concluded that Kerr-cell modulation of a near-infrared light beam (to 2 μ) is feasible. Kerr-cell modulation in the 2–15 μ region appears to be unfeasible; however, there may be a good possibility of such operation in the 15–25-μ range.