Theoretical modeling on resonating the second harmonic for ultraviolet laser generation

The resonance of the second harmonic was proposed to improve conversion efficiency in ultraviolet laser. A schematic to generate the fourth harmonic laser with a compound cavity was modeled based on plane-wave approximation. The simulated results show that the mode-matching condition of the multi-mode lasers depends strongly on both frequency-mode spacing and resonator loss. In the case of the same cavity lengths and losses, the tolerance on the optical cavity length should be maintained on tens or hundreds of nanometer scales. Meanwhile, the TEM₀₀ beam can be achieved due to the best mode-matching at resonance and the beam size increases arising from the cavity detune.     

High-order harmonic generation from metal plasmas using 1 kHz laser pulses

High-order harmonic generation in laser-produced plasma was demonstrated on metal surfaces using a high pulse repetition rate laser (1?kHz). It was found that if sufficiently thick bulk targets were used thermal conduction was sufficient to prevent any deterioration in the metal plasma plume production at this repetition rate. Under appropriate conditions harmonic yields were found to remain stable for >10⁵ laser shots without the need to move the target. The high repetition rate allowed both short and long electron trajectories to be clearly identified during harmonic generation from the metal plasmas.     

Estimating the plasmonic field enhancement using high-order harmonic generation: the role of the field inhomogeneity

In strong field laser physics it is a common practice to use the high-order harmonic cutoff to estimate the laser intensity of the pulse that generates the harmonic radiation. Based on semiclassical arguments it is possible to find a direct relationship between the maximum value of the photon energy and the laser intensity. This approach is only valid if the laser electric field driving the high-order harmonic radiation is spatially homogeneous. In laser–matter processes driven by plasmonics fields, the enhanced fields present a spatial dependence that strongly modifies the electron motion and consequently all the associated laser driven phenomena. As a result, this method should be revised in order to more realistically estimate the intensity of the laser field. In this work, we demonstrate how the inhomogeneity of the enhanced plasmonic fields will affect this estimation. Furthermore, by employing both quantum mechanical and classical calculations, we show how one can obtain a better estimation for the intensity of the enhanced field in plasmonic nanostructures.     

Numerical simulation of cascaded third harmonic generation for both phase matched and mismatched schemes

Numerical solutions to the nonlinear coupling-wave equations of second harmonic (SH) and third harmonic (TH) generators are investigated for both phase matched and phase mismatched configurations. For phase mismatched TH generation, several kinds of schemes (the phase mismatch either in second harmonic generation (SHG) or sum-frequency generation (SFG) process) are considered and analyzed. The physical nature corresponding to the different ratios of the coupling coefficients is discussed.     

Probing and modeling of carrier motion in organic devices by optical second harmonic generation

We here report a novel optical second harmonic generation (SHG) measurement that allows an electric field formed in organic solid to be probed. We examined the SHG intensity profile that changes depending on a space charge field caused by carrier injection. Experiments making use of time-resolved SHG technique has revealed dynamic changes of SHG intensity profiles arising from pentacene, and that carrier transport in OFET was diffusion-like. Calculations using drift-diffusion equation well accounted for the visualized carrier motion probed by time-resolved SHG. That is, interface charge propagation process dominates the carrier transport, which is regulated by applied gate-source voltage.     

Transient charge accumulation in pentacene field effect transistor with silver electrode

Time-resolved microscopic optical second harmonic generation (TRM-SHG) imaging was employed to study a transient charge accumulation in top-contact pentacene field effect transistor (FET) with Ag electrodes. It was demonstrated that the SHG signal at the edge of the Ag electrode decayed but remained in a steady state depending on biasing condition. An electric field formed in pentacene layer below Ag electrode activates the SHG, indicating the insufficient accumulation of injected carriers in the FET channel. By using the TRM-SHG technique transient change of the carrier density in the OFET is obtained.     

PREPARATlON AND OPTICAL PROPERTIES OF a-AXIS ORIENTED β-BaB_2O_4 SURFACE CRYSTALLIZED GLASS

采用传统熔融方法制备了透明ＢａＯ－Ｂ２Ｏ３玻璃。经受控热处理后,由ＸＲＤ谱发现存在ａ轴取向ＢＢＯ结构的微晶薄膜层。由Ｓｃｈｅｒｒｅｒ公式计算得出晶粒尺寸约２０ｎｍ。在１．０６４μｍＱ开关Ｎｄ：ＹＡＧ强激光作用下,观察到了倍频效应的产生（ＳＨＧ）。     

α轴取向β-BaB_2O_4表面析晶玻璃的制备及光学性质

采用传统熔融方法制备了透明BaO-B2O3玻璃.经受控热处理后，由XRD谱发现表面存在a轴取向BBO结构的微晶薄膜层,由Soberrer公式计算得出晶粒尺寸约20nm.在1.064μmQ开关Nd：YAG强激光作用下，观察到了倍频效应的产生（SHG）。     

Laser-parameter effects on the generation of ultrabroad harmonic and ultrashort attosecond pulse in a long-plus-short scheme

By numerically solving the time-dependent Schrödinger equation for helium gas in a special two-color laser field, which is synthesized by a long (9?fs) driving pulse and a short (6?fs) controlling pulse, we discuss the influence of the carrier-envelope phase, frequency, and the intensity of the controlling pulse on the generation of harmonic spectra and isolated attosecond pluses. In the cutoff region, two or three plateaus can be controlled by optimizing these laser parameters, and an ultrabroad supercontinuum harmonic spectrum with a bandwidth of 800?eV can be produced, which can support an ultrashort isolated 4.5 as pulse generation by Fourier transformation. Furthermore, using classical ionizing and returning energy maps, time–frequency analyses are presented to explain the underlying physical mechanisms.