Nanosecond Light Pulses Research Articles

Pulsed UV Laser-Induced Stationary Capillary Vibration for Highly Sensitive and Direct Detection of Capillary Electrophoresis

A stationary wave of the capillary vibration effect was successfully induced by a series of short laser pulses. This wave could be applied to highly sensitive detection of capillary electrophoresis as well as the already reported capillary vibration induced by an intensity-modulated CW laser (CVL effect). Generally, pulses with much shorter width than the period of the natural frequency of the vibrating system cannot induce a standing vibration. However, utilizing the time constant of CVL determined by heat dissipation time, we found conditions which could induce a stable stationary wave of the capillary by a series of nanosecond light pulses. We used the KrF excimer laser operated at 248 nm with a pulse width of 60 ns and output of ∼10 μJ/pulse as the CVL excitation source and applied it to highly sensitive detection of nonderivatized amino acids at the femtomole level. The sensitivity was at least 2 orders of magnitude superior to that of a commercially available UV absorbance detector. This technique extends the CVL's spectral regions. For example, in the UV region, where many biological materials have significant absorption bands, this technique will extend analytical applications in capillary electrophoresis by eliminating the need for a derivatization process.

Spectral holography of pico- and nanosecond optical pulses

Recording and reconstruction of pico- and nanosecond pulses have been accomplished with spectral holography. The development of spectral holography in the nanosecond time-domain was achieved while using high-spectral-resolution equipment based on a Fabry-Perot etalon with a side entrance/exit. The recognition of the shaped nanosecond light pulses was also realized.

Two-wave interaction of nanosecond laser pulses in CdTe crystals and the origin of their nonlinearity

An investigation was made of the formation of photorefractive gratings in CdTe crystals with an enhanced carrier (electron) mobility μ = 500 cm2 V-1 s-1 when they were excited by nanosecond light pulses. The photorefractive effect was separated in its pure form from the background of various nonlinear optical phenomena such as two-photon absorption, generation of nonequilibrium free carriers, and self-interaction of laser beams. The nature of the competing nonlinearity mechanisms was analysed.

Self-action of nanosecond light pulses in CdTe in degenerate two-wave mixing

Measurements are presented for the photorefractive effect in CdTe using 10-ns pulses at a wavelength of 1.06 μm. Different self-action effects that accompany two-beam coupling are discussed.

Use of broadband correlated nanosecond light pulses of different central frequencies in transient spectroscopy with picosecond and femtosecond resolution

Use of broadband correlated nanosecond light pulses of different central frequencies in transient spectroscopy with picosecond and femtosecond resolution

Trapping-states contributions to the optical nonlinearity of Cd(S,Se)-doped glasses

Wave-mixing and Z-scan experiments were performed in a study of the influence of the electronic trapping states on the nonlinear behavior of semiconductor-doped glasses. The origin of the optical nonlinearity for nanosecond light pulses whose frequencies were smaller than the sample band-gap frequencies was identified, and the densities of deep traps in the studied samples were measured.

Mapping of GaAs and Si wafers and ion-implanted layers by light-induced scattering and absorption of IR light

The methods of light-induced absorption and diffraction have been used to investigate the uniformity of Si and GaAs wafers and ion-implanted Si. Metastable annealing of defects, lifetime modification by swirl and radiation defects and anomalous depth penetration of ion-implantation-created defects have been demonstrated in Si. The mapping of GaAs wafers has been performed with picosecond and nanosecond light pulses and light absorption mechanisms are discussed.

Energy exchange between optical waves due to self-diffraction by photorefractive gratings in a CdTe crystal

Theoretical and experimental investigations were made of a photorefractive nonlinearity of CdTe semiconductor crystals. Photorefractive gratings were formed in undoped CdTe and used to provide efficient energy exchange between nanosecond pulsed light beams (λ ≈ 1.06 μm) characterized by an exchange gain of ~ 0.13 cm − 1.

Reaching the shot noise limit in the polarization measurement of individual nanosecond light pulses

Using a balanced dual-channel polarimeter and fast photodiodes coupled to low-noise charge integrators, we demonstrate precise polarization detection of individual light pulses in the nanosecond time-scale, with a noise very close to the shot noise limit. This result has important implications for various precision measurements such as atomic parity violation, squeezing at short time scales, and possibly parity violation with squeezed light.

Photorefractive beam coupling in GaAs and InP generated by nanosecond light pulses

Energy transfer between two nanosecond light pulses interacting in semi-insulating 4¯3m crystals is studied. By using the specific dependences of the photorefractive effect on wave polarizations and crystal orientation, the contribution of this to two-wave mixing in GaAs and InP is analyzed.

Temporal behaviour of bistable ZnSe interference filters switched by nanosecond light pulses: Dependence upon the pulse energy

Fast nanosecond switching times in ZnSe bistable nonlinear interference filters have been reported previously. The samples were excited by a cw holding argon laser and a pulsed excimer laser. In this paper, the pulse energy dependence of the switching time is studied. It appears that the pulse energy must be chosen precisely to obtain optimum performances of the device. Since the switching is related to a “thermal” shift of the interference fringe towards the argon laser wavelength, a three-beam experiment has been performed to investigate simultaneously the spectral shift of the fringe and the switching dynamics.

Mechanism of formation of a volume discharge initiated by a barrier discharge distributed on the surface of a cathode

A study was made of the mechanisms of formation of a self-sustained volume discharge in CO2–N2–He gas mixtures initiated by an auxiliary barrier discharge distributed on the surface of a cathode. The volume discharge was initiated when the discharge gap was filled by an electron flux formed from the barrier discharge plasma in the course of a smooth rise of the voltage across the electrodes. Measurements were made of the small-signal gain confirming the model of formation of a self-sustained volume discharge and demonstrating that a discharge of this kind could be used to amplify nanosecond light pulses.

Transient photocurrent induced by nanosecond light pulses in BSO and BGO

We investigate photoconductive decay following a fast 3-ns light pulse excitation in bismuth silicium oxyde (Bi 12SiO 20) and bismuth germanium oxyde (Bi 12GeO 20) single crystals of different origins. According to the different studied samples, photoconductive decay times of 50 ns and even smaller than 3 ns are observed. These decay times are due to electron recombination time from the conduction band. If we try to obtain the electron mobility in the conduction band, which seems several orders of magnitude greater than usual mobility values, it appears necessary to determine a precise diffusion length value.

Rayleigh scattering of nanosecond light pulses

The relation σΔt/σtheory = (τ1/τ)[−exp(−Δt/τ)], obtained by M. Skowronek and J. Alayli for Rayleigh scattering of light pulses, is experimentally investigated. Relative measurements of scattering are made in Ar and N2 without taking into account instrumental effects. It is shown that the level of scattering in a gas medium is independent of the pulse duration Δt for a pulse with a wavelength of λ = 0.53 μm in the range 2 ns ⩽ Δt ⩽ 30 ns.

Light pulse compression in a glass fiber amplifier

It has been experimentally shown that when light pulses propagate in active neodymium glass fibers, a decrease of amplified pulse length almost by a factor of two is observed at a fiber length of 1 m. The study of the amplification process of an ultrashort laser pulse train by a glass fiber quantum amplifier showed that the main reason of the nanosecond light pulse compression is a recombination of the short-lifetime colouring centers due to the absorption of the front of the light pulse. Experimental results are presented concerning light pulse compression at various excitation levels of active glass fibers.

Shortening of light pulses in a glass-fiber amplifier

It was demonstrated experimentally that propagation of light pulses in active neodymium-doped glass fibers reduced the duration of the amplified pulses almost twofold in fibers 1-m long. A study of the amplification of a series of ultrashort laser pulses carried out using a glass-fiber quantum amplifier showed that the main cause of reduction in the duration of nanosecond light pulses was recombination of short-lived color centers because of the absorption of the leading edge. The shortening of light pulses was studied at different rates of excitation of active fiber waveguides.

Measurements of the Relaxation Kinetics of Photo‐Excited Enol Form of Dibenzoylmethane

The decay rate of the excited state of the enol form of dibenzoylmethane (DBM) in different solvents is measured directly using nanosecond light pulses. The observed relaxation kinetics is explained by the formation of three intermediate forms of the excited cis‐enol form of DBM. The decay rates of the intermediates and their absorption cross sections for λ = 266 nm are reported too.

Generation of widely tunable nanosecond pulses in the vibrational infrared by stimulated Raman scattering from the cesium 6s–5d transition

The first reported use of a pulsed rhodamine-dye laser to generate widely tunable nanosecond light pulses in the vibrational infrared by stimulated electronic Raman scattering is discussed. Narrow-band pulses of up to 120 microJ were generated from 3450 to 900 cm(-1) (2.9 to 11.1 microm), and broadband pulses up to 75 microJ were generated from 3390 to 1800 cm(-1) (2.9 to 5.5 microm) by scattering from the 6s-5d transition in cesium vapor. Cesium dimer effects on tuning-curve structure and efficiency are discussed.

Time-delayed photoelectric effect

The Einstein photoelectric relation1 initially explained the photoelectric effect, hν=Tmax + Eb where hν is the energy of a photon incident on a material, Eb is the binding energy of the electron to be excited, and Tmax is the maximum kinetic energy of the emitted electron. This work has generated considerable research2–5 because of its multidisciplinary interest. We describe here photoelectric emission (PE) experiments using very low-intensity nanosecond light pulses with energies near the PE threshold. Signal correlated, time-delayed pulses of emitted electrons were observed for single light pulses incident on a photosensitive material. However, the energies of the delayed emitted electrons were not correlated to the wavelength of the incident light, which is not consistent with Einstein's relation. At higher incident light intensities, the delayed pulses were not observed. These pulses were not due to electrical noise because they disappeared when the laser light was blocked from entering the cell. They were not due to single photon luminescence from a particular species because the pulses were observed using another experimental apparatus with an alternate source of nanosecond light. We now describe these delayed pulses and give a preliminary interpretation of them.

Reversal of the wavefront of nanosecond and subnanosecond light pulses in stimulated Brillouin scattering

An experimental investigation was made of the wavefront reversal parameters and of the reflection coefficient of a stimulated Brillouin scattering mirror made of CCl4; the measurements were carried out in a wide range of pump energies using pulses of 0.5–10 nsec duration. A reduction in the pulse duration reduced the dynamic range (i.e., the range of the pump energies) in which wavefront reversal was observed. Specially shaped pulses with different values of the contrast were used for the reversal of radiation with a high peak power.