Synchronized Laser Pulses Research Articles

Projection ablation of glass-based single and arrayed microstructures using excimer laser

Ablation of single and arrayed microstructures using an excimer laser is studied. The single feature microstructures are fabricated for evaluating the ablation mechanism, threshold fluence, and associated material removing (ablation) rate. The morphology changes during ablation are investigated with the focus on the formation of the ablation defects, debris or recast. The possibility of removing these defects is also evaluated and demonstrated. The present study concentrates on the borosilicate glass, although ablation of polyimide and silicon are performed and discussed for comparison. Polyimide and silicon are the most popular polymer or semiconductor material used in the electronics industry. The arrayed microstructures are ablated to demonstrate the fact that, by repetition of a simple-patterned mask associated with synchronized laser pulses and substrate movement, arrayed and more complex structures can be cost-effectively manufactured. The potential applications of these arrayed microstructures are discussed and illustrated. A low-cost replication technique that uses the arrayed microstructure presently machined as the forming mold for making electroforming nickel microneedles is specifically presented. Finally, the potential areas of using excimer laser in micromachining of glass-based structures for future research are also briefly covered.

Photostability of a fluorescent marker under pulsed excited-state depletion through stimulated emission.

Saturated stimulated-emission depletion (STED) of a fluorescent marker has been shown to break the diffraction barrier in far-field fluorescence microscopy and to facilitate spatial resolution down to a few tens of nanometers. Here we investigate the photostability of a fluorophore that, in this concept, is repeatedly excited and depleted by synchronized laser pulses. Our study of bacteria labeled with RH-414, a membrane marker, reveals that increasing the duration of the STED pulse from approximately 10 to 160 ps fundamentally improves the photostability of the dye. At the same time the STED efficiency is maintained. The observed photobleaching of RH-414 is due primarily to multiphoton absorption from its ground state. One can counteract photobleaching by employing STED pulses that range from 150 ps to approximately half of the lifetime of the excited state. The results also have implications for multiphoton excitation microscopy.

Synchronization of chaos in microchip lasers by using incoherent feedback.

We propose a chaos-synchronization scheme using incoherent feedback to the pumping power in two microchip lasers. The population inversion of the slave laser is controlled for synchronization by using the detected signals of the peak heights of chaotic pulse intensities in the two lasers. Matching of the optical frequencies between the two lasers (i.e., injection locking) is not required for synchronization using this method. We numerically demonstrate the incoherent feedback method and investigate synchronization regions against parameter mismatching between the two lasers. Synchronization is maintained within a mismatching of 1% for all laser parameters, which implies that the difficulty in reproducing the synchronized laser pulses is very useful for applications of secure optical communications.

Probing transient molecular structures with time-resolved pump/probe XAFS using synchrotron X-ray sources

Laser pulse pump, X-ray pulse probe X-ray absorption fine structure (pump-probe XAFS) experiments using synchrotron sources are described from technical considerations and from scientific significance. There are three technical challenges of such experiments: (1) laser photoexcitation, (2) synchronization of laser pulse and X-ray pulse, and (3) detection; each of which is investigated in detail. Based on the results from these investigations, the transient molecular structure of a reaction intermediate produced by photoexcitation of NiTPP-L 2 (NiTPP, nickeltetraphenylporphyrin; L, piperidine) in solution has been captured for the first time with the pump-probe XAFS on a 14-ns time scale obtained from the X-ray pulses from a third generation synchrotron source. The experimental results confirm that photoexcitation leads to the rapid removal of both axial ligands to produce a transient square-planar intermediate, NiTTP, with a lifetime of 28 ns. The transient structure of the photodissociated intermediate is nearly identical to that of the ground state NiTPP, suggesting that the intermediate adopts the same structure as the ground state in a non-coordinating solvent before it recombines with two ligands to form the more stable octahedrally coordinated NiTPP-L 2 . No detectable population of a penta-coordinated intermediate was present. This experiment demonstrates the feasibility of determining transient molecular structures in disordered media using the temporal resolution of a synchrotron X-ray source.

Novel technique for low-jitter dual-laser synchronization in a thin film deposition system

The need for precise laser pulse synchronization in a dual-laser ablation system to optimize the quality of the deposited thin films has been previously demonstrated. We present, in this article, a novel technique for the synchronization of an excimer and a CO2 laser with synchronization having a temporal fluctuation (jitter) of less than ±14 ns. This is several times better than the best precision of temporal synchronization possible using traditional electronic techniques and is crucial for the application of dual-laser ablation in the manufacturing of thin films. Evidence for reproducibility in the ablation of targets using this system is presented by analyzing the initial stages of the ablated plasma using a time-gated charge coupled device imaging system.

Measurement of the temporal evolution of periodic induced displacement derivatives using stroboscopic electronic speckle-shearing interferometry

Single pulsed subtraction electronic speckle-shearing pattern interferometry is used to measure the time evolution of deformations induced by periodic impulse loading on a metal plate. This is accomplished with a stroboscopic system based on a pulsed laser and an interline-transfer CCD camera running at 60 frames/s. In a few seconds, a sequence of hundreds of interferograms is recorded with an effective sampling time interval of some tens of microseconds. We describe the experimental setup used to generate the transient deformation on the metal plate and also the synchronization of laser pulses and image acquisition. Several correlation fringe patterns are presented, showing the time evolution of the deformation. Finally, these data are used to calculate optical phase maps and displacement derivative fields for different times after the application of the dynamic load on the object.

An incoherent sub-picosecond X-ray source for time-resolved X-ray-diffraction experiments

Ultrashort bursts of K α X-ray radiation were generated from fs-laser-produced plasmas. A complete experimental characterization of the X-ray source in terms of spectral, spatial, and temporal properties was performed. The pulse width of the K α burst is shorter than 250 fs. The time-resolved evolution of a shock wave launched by a synchronized laser pulse in InSb was investigated. The transient change of the rocking curve yields detailed information on the structural changes.

Multi-terawatt hybrid Ti:SaNd:glass dual-beam laser: a novel XUV laser driver

A hybrid Ti:Sa Nd:glass laser is described delivering two synchronized laser pulses with duration of 0.7 ps and 1.2 ns and output energies of 4 J in the short pulse and 8 J in the long pulse. The system was successfully used to drive efficiently a transient inversion XUV laser on [Ne]-like ions [see Nickles et al., SPIE Vol. 2520].

Resonant ionization using synchronized laser pulses

The resonant ionization of gold atoms has been investigated using two synchronized laser pulses — a heating pulse from a Nd-Yag laser to desorb atoms from the substrate, and a pulse from an excimer-laser-pumped dye laser for resonant ionization. The 532-nm beam was found to be most suitable for desorption. With a power density of 5 × 10 7 W cm −2 for the ionization beam, the linewidth for the [5d 106s → 5d 106p] transition in gold was measured to be 180±10 GHz. Using long-lived 194–196,198Au isotopes evaporated onto a tantalum substrate, an overall ion-collection efficiency of (1.0±0.5)×10 −4 was obtained. Geometric constraints of the experimental setup account for a loss factor of 3×10 −3, while the remaining reduction factor of 3.3×10 −2 is attributed to incomplete desorption into single atoms, non-saturation of the ionization process, low ion-collection efficiency, and losses due to ion-atom collisions.

On the possibility to measure volumes of small gas bubbles and the bubble producing gas flow rates acoustically

Using the pulsation properties of gas bubbles it is possible to measure acoustically volumes c.q. equivalent diameters of gas bubbles in the range of 1.8–2.1 mm, produced at low frequencies at capillary tubes in a silent environment. Hence it is possible to measure very low gas flow rates (from 4 up to 100 mm3/s). During formation of bubbles at capillary tubes phenomena of repeated coalescence can occur between a just released bubble and the following bubbles under formation. This occurrence depends on the speed of rise, the bubble volume and the formation frequency. There is experimental evidence that this swallowing-up gives cause to a swinging-up of the amplitude of the pulsation signal. This coalescence process is the main physical limitation of the claimed method to low frequencies. There is also some experimental evidence by laser pulse synchronization between acoustics and bubble photographs that the often reported neck during bubble formation actually is an effect caused by this swallowing-up process.

A double-pulse laser oscillator with a continuously variable time interval between the pulses

A description is given of a possible method for obtaining two synchronized laser pulses, separated in space and time. The system proposed provides a continuously variable time interval between the laser pulses (of energy 0.3 J and pulse length 25–50 nsec) over the range 0–15 μsec, and it can be used for synchronizing the triggering of various devices and photographic recording of objects and processes over a wide time interval.

K3 Plasma diagnostics with ultrashort synchronized laser pulses

K3 Plasma diagnostics with ultrashort synchronized laser pulses