Pulse duration

About: Pulse duration is a research topic. Over the lifetime, 19429 publications have been published within this topic receiving 286507 citations.

Role of laser-pulse duration in the neutron yield of deuterium cluster targets

Abstract: We present an experimental and computational study of the ion and fusion neutron yields from explosions of deuterium clusters irradiated with 100-TW laser pulses. We find that the cluster explosion energy and resultant fusion yield are sensitive to the laser pulse rise time as determined by the pulse duration for a fixed envelope shape. Our experimental observations are consistent with the results of particle simulations of the laser-cluster interaction which show that the explosion energies of the clusters are determined by a single parameter: the ratio of the cluster ionization time to its intrinsic expansion time. This competition of time scales sets a fundamental constraint on the ion emission and resultant neutron yield performance of these targets as a function of laser-pulse duration.

Near-field radiofrequency thermoacoustic tomography with impulse excitation.

Abstract: Purpose: Imaging performance of radiofrequency and microwave-based thermoacoustictomography systems is mainly determined by the ability to deposit a substantial amount of electromagnetic energy within ultrashort time duration. Pulses of nanosecond-range duration that can carry hundreds of millijoules energy are ideal for obtaining good signal-to-noise and spatial resolution in many biological imaging applications. However, existing implementations are based on modulated-carrier-frequency amplification solutions, which are generally costly and cannot achieve ultrahigh-peak-power requirements essential for optimal thermoacoustic signal generation. Methods: Herein the authors suggest and experimentally validate a near-field radiofrequency tomography (NRT) method for high resolution imaging of biological tissues using ultrashort electromagnetic impulses. The solution includes a low-cost pulsing system while the imaged objects are placed in the near field of the energy-emitting aperture for improved coupling using nonradiative fields. Results: In the current design, the authors were able to achieve excitation impulse energies of hundreds of millijoules with durations in the order of a few nanoseconds, corresponding to peak power levels of multiple megawatts. The phantom imaging experiments demonstrated image features with characteristic sizes of around 170 μ m , but the impulse durations used herein allow in principle spatial resolutions in the order of a few tens of microns when using an appropriate ultrasonic detection bandwidth. Conclusions: The proposed NRT method makes it possible to attain very high spatial resolution without compromising the thermoacoustic signal strength. This makes the imaging performance to be limited by the available bandwidth of the ultrasonic detector rather than by the microwave pulse duration. It is overall expected that the combination of pulsed near-field coupling with optimal choice of energy dissipation elements will generate a practical modality that can scale its application to small and larger volumes alike, while optimally adjusting the resolution to match the acoustic resolution possible. Such an approach should find several applications in small animal and clinical imaging.

Cryogenic Yb 3+ -doped materials for pulsed solid-state laser applications [Invited]

Abstract: We review recent progress in pulsed lasers using cryogenically-cooled Yb3+-doped gain media, with an emphasis on high average power. Recent measurements of thermo-optic properties for various host materials at both room and cryogenic temperature are presented, including thermal conductivity, coefficient of thermal expansion and refractive index. Host materials reviewed include Y2O3, Lu2O3, Sc2O3, YLF, YSO, GSAG and YVO4. We report on the performance of several cryogenic Yb lasers operating at 5-kHz pulse repetition frequency (PRF). A Q-switched Yb:YAG laser is shown to operate at 114-W average power, with 16-ns pulse duration. A chirped pulse amplifier achieves 115-W output using a Yb:YAG power amplifier. Output power of 73 W is obtained from a composite Yb:YAG/Yb:GSAG amplifier, with pulses that compress to 1.6 ps. Finally, a high-average-power femtosecond laser based on Yb:YLF is discussed, with results for a 10-W regenerative amplifier at 10-kHZ PRF.

All-fiber dissipative soliton laser with 10.2?nJ pulse energy using an evanescent field interaction with graphene saturable absorber

Abstract: We demonstrate a high-power dissipative soliton fiber laser by employing an evanescent field-coupled graphene saturable absorber (SA). In the SA, a polymer supporter enhances the nonlinear interaction between the guided mode and the high-quality graphene layers, which enables high-power operation of the mode-locked laser in the normal dispersion regime of the laser cavity. A self-started dissipative soliton fiber laser stably generates pulses with a spectral bandwidth of 10.4 nm at 1565 nm. The linearly chirped pulse of the laser output has a pulse duration of 13.8 ps at a repetition rate of 16.99 MHz. The maximum output power achieved is 174 mW using a single-mode pump laser diode with an applied power of 785 mW. The pulse energy is estimated to be 10.2 nJ; we believe this is the highest pulse energy ever reported for an Er-doped dissipative soliton fiber laser oscillator using a graphene SA.