Fsec Pulses Research Articles

Ptychographic ultrahigh-speed imaging.

We propose and demonstrate numerically a simple method for ultrahigh-speed imaging of complex (amplitude and phase) samples. Our method exploits redundancy in single-shot ptychography (SSP) for reconstruction of multiple frames from a single camera snapshot. We term the method Time-resolved Imaging by Multiplexed Ptychography (TIMP). We demonstrate TIMP numerically-reconstructing 15 frames of a complexed-valued dynamic object from a single noisy camera snapshot. Experimentally, we demonstrate SSP with single pulse illumination with pulse duration of 150 psec, where its spectral bandwidth can support 30 fsec pulses.

The use of femto-second lasers to trigger powerful explosions of gold nanorods to destroy cancer cells

Gold nanorods (AuNRs) with an aspect ratio of 3–4 exhibit large cross sections for single and multi photon light absorption processes in the near infrared region due to surface plasmon resonances. 800 nm laser pulses with the 150 fsec pulse duration (fs laser) can trigger explosions of AuNRs. The fs laser pulses at 20 W/mm2 equivalent continuous wave (cw) power density blasted AuNRs in QGY human carcinoma cells as confirmed using transmission electron microscopy, while a cw laser at the same power density and dose did not. Cell survival studies further demonstrated that the cw laser at a dose of 15 J/mm2 resulted in the death of 15% of AuNRs-loaded cells, probably due to a photothermal effect, while the fs laser at only 1.5 J/mm2 killed more than 90% of AuNRs-loaded cells, indicating that the fs laser-triggered explosions of intracellular AuNRs are powerful enough to instantaneously kill tumour cells.

Charge separation in photosynthetic reaction centers under femtosecond excitation.

The process of electron transfer from the primary electron donor P* to the primary electron acceptor BA in the reaction center of Rhodobacter sphaeroides R-26 under 30 fsec pulse excitation was studied in this work with the aim of establishing a relationship between the nuclear subsystem motion and charge transfer. For this purpose the fsec and psec oscillations in the bands of stimulated emission of P* and in the band of reaction product BA- at 1020 nm were investigated. It was established that the reversible formation of the P+BA- state is characterized by two vibration modes (130 and 320 cm(-1)) and connected with an arrival of the wavepacket induced by fsec excitation to the intersection of potential surfaces P*BA and P+BA-. The irreversible formation of the P+BA- state with the time constant of 3 psec is followed by oscillations with frequencies of 9 and 33 cm(-1). These results show that the irreversibility of electron transfer is determined by two factors: 1) by a difference between the energy width of the wavepacket and the gap between the named surfaces; 2) by a difference between the duration of wavepacket residence near the intersection of the surfaces and the relaxation time of the P+BA- state.

Time-dependent H-like and He-like al lines produced by ultra-short pulse laser

We perform numerical modeling of time-resolved x-ray spectra from thin foil targets heated by the LLNL Ultra-short pulse (USP) laser. The targets were aluminum foils of thickness ranging from 250 to 1250 A, heated with 120 fsec pulses of 400 nm light from the USP laser. The laser energy was approximately 0.2 J focused to a 3 μm spot size for a peak intensity near 2 × 10 19 W/cm 2. Lyoe and Heα lines were recorded using a 900 fsec x-ray streak camera. We calculate the effective ionization, recombination and emission rate coefficients including density effects for H-like and He-like aluminum ions using a collisional-radiative model. We calculate time-dependent ion abundances using these effective ionization and recombination rate coefficients. The time-dependent electron temperature and density used in the calculation are based on an analytical model for the hydrodynamic expansion of the target foils. During the laser pulse the target is ionized. After the laser heating stops, the plasma begins to recombine. Using the calculated time-dependent ion abundances and the effective emission rate coefficients, we calculate the time-dependent Lyα and Heα lines. The calculations reproduce the main qualitative features of the experimental spectra. We also calculate the He-like spectra including satellite lines.

Inactivation of Pseudomonas fluorescens by High Voltage Electric Pulses

ABSTRACTA 30 kV pulsed power treatment system was designed and developed to process fluid materials. Our objective was to investigate the effects of high voltage electric pulses on microbial inactivation in an aqueous solution under different operating conditions and fluid properties. Electric field strength at 10 kV/cm for 10 pulses (2 set pulse period and 2 Fsec pulse width) with a spike of reverse polarity resulted in significant microbial control. P. fluorescens in various aqueous solutions were reduced in population by more than six log cycles. However, the critical electric field strength was affected by the nature of the pulse waveform across the treatment chamber which, in turn, was a function of electrode distance and fluid properties. Sudden charge reversal immediately at the end of a pulse provided maximum microbial decay.

PUSHING THE LIMITS of Femtosecond Technology: Chirped Dielectric Mirrors

The authors explain the theory behind ultrashort pulses and offer a new method — chirped dielectric mirrors — for achieving sub-10 fsec pulses.

Time-domain wave propagation in optical structures

To make time-domain computation more efficient in optical structures, the wave equation is rewritten to track only the envelope of the electric field. The resultant equation is complex in nature and it is solved via a mapping concept and a Pade approximation. Compared to the finite-difference time-domain algorithm, this method takes two orders of magnitude less memory. This method is applied to the propagation of a 500 fsec pulse in a waveguide over 2 mm. Transient behavior and the effects of waveguide parameters are demonstrated. >