A simple scaling of bulk laser-induced breakdown threshold for wide band-gap solids is derived on the basis of a recent modification
of the Keldysh photo-ionization model [43, 46]. Contrary to most traditional models, the modification is based on rigorous
energy dependence of reduced effective electron–hole mass. The dependence leads to a specific ionization regime with an extremely
high ionization rate resulting in intensive generation of conduction-band electrons. The regime is characterized by a well-determined
threshold intensity that is proposed to be associated with the threshold of bulk intrinsic laser-induced breakdown (LIB) by
visible and near-infra-red laser radiation. That allows deriving dependence of LIB threshold on laser and material parameters.
The presented model provides explanation for the experimental results on LIB thresholds that have not received theoretical
interpretation. In particular, it reproduces empirical dependence of breakdown threshold on the average inter-atomic spacing
derived from the experimental data. The LIB threshold evaluated from the presented model is very close to experimental data
on bulk LIB by tightly focused beams in wide band-gap solids.
PACS 78.47.+p; 42.50.Hz; 42.50.Ct 相似文献
The air breakdown is easily caused by the high-power microwave, which can have two mutually orthogonal and heterophase electric field components. For this case, the electron momentum conservation equation is employed to deduce the electric field power and effective electric field for heating electrons. Then the formula of the electric field power is introduced into the global model to simulate the air breakdown. The breakdown prediction from the global model agrees well with the experimental data. Simulation results show that the electron temperature is sensitive to the phase difference between the two electron field components, while the latter can affect obviously the growth of the electron density at low electron temperature amplitudes. The ionization of nitrogen and oxygen induces the growth of electron density, and the density loss due to the dissociative attachment and dissociative recombination is obvious only at low electron temperatures. 相似文献
This paper investigates the wavelength dependence of the threshold of gold nanorod‐mediated optical breakdown during picosecond and femtosecond near infrared optical pulses. It was found that the wavelength dependence in the picosecond regime is governed solely by the changes of a nanorod's optical properties. On the other hand, the optical breakdown threshold during femtosecond pulse exposure falls within one of two regimes. When the ratio of the maximum electric field from the outside to the inside of the nanorod is less then 7 (the absorption regime) the seed electrons are initiated by photo‐thermal emission, and the wavelength dependence in the threshold of optical breakdown is the result of optical properties of the nanoparticle. When the ratio is greater than 7 (the near‐field regime) more seed electrons are initiated by multiphoton ionization, and the wavelength dependence of the threshold of optical breakdown results from a combination of nanorod's optical properties and transitions in the order of multiphoton ionization. The findings of this study can guide the design of nanoparticle based optical breakdown applications. This analysis also deepens the understanding of nanoparticle‐mediated laser induced breakdown for picosecond and femtosecond pulses at near infrared wavelengths.
An investigation of the unexpectedly strong dependence of the threshold intensity on the gas pressure in the experimental study on the breakdown of He by short laser wavelength (Turcu et al., in Opt Commun, 134:66–68, 1997) is presented. A modified electron cascade model is applied (Evans and Gamal, in J Phys D Appl Phys, 13:1447–1458, 1980). Computations revealed reasonable agreement between the calculated thresholds and the measured ones. Moreover, the calculated electron energy distribution function and its parameters proved that multiphoton ionization of ground and excited atoms is the main source for the seed electrons, which contributes to the breakdown of helium. The effect of diffusion losses over pressures <1,000 Torr elucidated the origin of the strong dependence of the threshold intensity on the gas pressure. Collisional ionization dominates only at high pressures. No evidence for recombination losses is observed for pressures up to 3,000 Torr. 相似文献
Single-shot laser damage threshold of MgO for 40-986 fs, 800 nm laser pulses is reported. The pump-probe measurements with femtosecond pulses were carried out to investigate the time-resolved electronic excitation processes. A theoretical model including conduction band electrons (CBE) production and laser energy deposition was applied to discuss the roles of multiphoton ionization (MPI) and avalanche ionization in femtosecond laser-induced dielectric breakdown. The results indicate that avalanche ionization plays the dominant role in the femtosecond laser-induced breakdown in MgO near the damage threshold. 相似文献
The morphology just above threshold of damage sites caused by picosecond 1.06 μm laser pulses is shown to consist of a collection of micron-sized, spatially distinct vestiges of individual plasmas. From the observed site density, the density of electrons which may initiate breakdown can be inferred. The morphology is consistent with an avalanche ionization model, but not with absorbing inclusion damage. 相似文献
A set of experimental dependences of the air ionization effective rate on the electric field strength is presented. The concept of the critical breakdown field is discussed. It is indicated that experimental data are quantitatively inconsistent with analytical results based on this concept. This inconsistency is eliminated if the ionization balance takes into account not only dissociative adhesion of electrons to oxygen molecules but also their detachment from the molecules that gained a charge during the charge exchange process. Based on the results obtained, a new physical interpretation of the critical field is suggested. A formula for the effective rate of air ionization in near-critical fields is derived. 相似文献
We suggest a simple approach to roughly estimate the excitation cross sections of various steps in a multiphoton ionization (or dissociation) process by applying the measured dependence of product signal on laser intensity. The validity of this method is demonstrated theoretically by means of the rate equations based upon a two-step kinetic model and can, in principle, be extended to the multiphoton process with steps more than two. Some results of numerical test and experiment are quoted. 相似文献
One- and two-step rapid thermal annealing (RTA) for activating Mg-doped p-type GaN films had been performed to compare with conventional furnace annealing (CFA). The two-step annealing process consists of two annealing steps: the first step is performed at 750 °C for 1 min and the second step is performed at 600 °C for 5 min in pure O2 or air ambient. It is found that the samples annealed in air ambient exhibit poor electrical properties as compared to those annealed in pure O2. Compared to one-step RTA annealing and CFA annealing, the samples with two-step annealing exhibit higher hole concentration and lower resistivity. This means that the two-step annealing is a powerful method to enhance the electrical performance of Mg-doped p-type GaN films. Similar results were also evidenced by photoluminescence (PL) measurement. Possible mechanism was confirmed by secondary ion mass spectrometry analysis. 相似文献