Short Laser Research Articles

S131012 微細深穴のトレハニング加工に関する研究

S131012 微細深穴のトレハニング加工に関する研究

Novel concept for laser patterning of thin film solar cells

AbstractLasers are increasingly being used as an efficient and reliable tool in the production of solar cells and solar modules. Particular interest exists in thin‐film photovoltaics, where laser structuring is aimed to realize appropriate monolithic serial interconnection. A novel concept successfully demonstrated complete laser structuring by application of short nanosecond laser pulses with a single, visible wavelength. These results promise further simplification and flexibility to thin film solar cell production.

Hot spot heating process estimate using a laser-accelerated quasi-Maxwellian deuteron beam

AbstractThe hot spot heating process by an assumed deuteron beam is evaluated in order to estimate the contribution of the energy produced by the deuteron beam-target fusion to the heating process. The deuteron beam energy versus the number of deuterons is evaluated through the experimentally achieved proton beam energy distribution using the TRIDENT short pulse laser at the Los Alamos National Laboratory (LANL). The corresponding hot spot heating is then calculated using this assumed deuteron beam spectrum. The resulting first order heating dynamics is employed in the expanded “bonus” energy calculation, and a 12.73% extra energy from deuteron beam-target fusion was found with the assumed deuteron spectrum when ρrb = 4.5 g/cm2 is considered, where ρ is the fuel density, and rb is the ion beam focusing radius on the target. The results provide further insight into the contribution of the extra heat produced by deuteron beam-target fusion to the hot spot ignition process. A further analysis of how a converter foil using ultra-high-density cluster materials can help to achieve the yield requirements for ignition is presented.

Computer simulation of the propagation of extremely short femtosecond pulse in single-mode fiber with shifted dispersion characteristics

We present the results of theoretical study of generation of spectral supercontinuum by an extremely short femtosecond laser pulse with the central wavelength corresponding to zero dispersion, propagating in a single-mode fiber with shifted dispersion characteristics. High-order nonlinear Schrodinger equation (HONSE) is considered with higher-order terms taken into account. Numerical integration of HONSE is performed by the method of lines. Time dependence of instantaneous frequencies of the femtosecond pulse is obtained. The evolution of the pulse spectrum is calculated and the medium length dependence of the spectrum width is obtained. For study of the time-frequency dynamics of extremely short femtosecond laser pulse propagating in single-mode optical fiber with allowance for higher order terms, the Wigner transformation (WT) was used.

Ionization and population transfer in lithium Rydberg states with ultrashort chirped laser pulses

We present a theoretical study of dynamics of Rydberg states of lithium using ultra short chirped laser pulse having a Gaussian envelope. The population transfer probabilities are calculated of different Rydberg states on chirped laser factors. The calculations are performed by direct numerical integration of Schrodinger equation using fourth order Runge-Kutta method. The behavior of dynamics of Rydberg states for these factors is of great significance. These results are of potential interest in coherent quantum control, quantum computation and in many physical and chemical processes.

Development of Chip Separation Technique for InGaN-Based Light Emitting Diodes

We compare the chip separation techniques for InGaN-based light emitting diode (LED), which are prepared by conventional diamond tip scribing and short pulse laser scribing with pulse width of nanosecond or femtosecond. Differently from the diamond tip scribing, the laser scribing does not suffer from the shallow scribing depth, which usually results in a failure in cleaving the wafer along the scribed line. Furthermore, the LED scribed by using a femtosecond pulse laser exhibits an 11% enhancement in the output power at 20 mA, compared to that by using a nanosecond pulse laser. This is because the femtosecond laser scribing not only eliminates particle generation, but also minimizes the effect of thermal damage on the sapphire substrate. The femtosecond laser also offers a high speed, high yield, and hence low cost scribing process due to its extremely short pulse width and deep focal length.

Single Step Generation of Micro and Radio Wave Signals in a Short Cavity Fiber Laser

Generation of stable micro or radio waves by frequency down-conversion has always been a challenging but rewarding task in radio over fiber systems. In this letter, a novel method for such a generation using a short-cavity fiber laser is demonstrated. For this purpose, an all-fiber laser is designed to have two stable longitudinal laser modes, each of them having two orthogonal polarization modes. Hence, four microwave signals, two in 1.2 GHz range and the other two in 14 GHz range, and one radio wave signal were generated by beating these lasing modes on a square law detector. Various measurements show high level of stability in generated micro/radio waves because they originate from the single laser cavity. According to the authors' knowledge, this is the first demonstration of the dual longitudinal mode operation of a short-cavity fiber laser for down-conversion from optical frequency directly to radio frequency.

Conical emission in focused beams: analysis of contributing factors and elimination of scattering

We report a detailed analysis of experimental parameters and fundamental mechanisms contributing to the strong nonlinear scattering of femtosecond and short picosecond laser pulses (50–6000 fs) at focusing in ambient air and protecting gases. The experimental conditions under consideration are typical for a variety of applications: micromachining of metals and dielectrics, high power laser exposure of targets. Such scattering, being the most noticeable manifestation of the complex phenomenon of conical emission in the focusing geometry, puts fundamental limitations to the incident power of precision laser targeting, restricting in this way potential productivity of micromachining in this pulse width range. The phenomena analyzed here are: ionization, the optical Kerr effect, the distortion of spectra via self-phase modulation, and the refractive ability of microplasma, namely the scattering. Characteristics of the last were investigated with respect to the incident wavelength and pulse width, for focusing of Gaussian and flat-top beams of different diameters. The obtained extensive data allowed us to trace the clue trends and relationships of this phenomenon and to find several ways to reduce or even eliminate the scattering in a broad range of the incident energies.

Interaction of intense ultrashort laser pulse with shell target

Based on numerical PIC modeling and an analytical model, we analyze the interaction of a short high-intensity laser pulse with homo- and heterogeneous (two-layer) shell targets. We show that the shell target is capable of focusing ions in a narrow region. In this case, the ion energy exceeds the ion energy for a flat infinite target of the same thickness. We propose to use the effect of focusing and cumulation of ions to implement the collision of ionic beams that counterpropagate from opposite sides of the sphere and to increase the yield of ion-ion reactions. The constructed model makes it possible to calculate the energy of the ion and the number of ions in the region of focusing.

Relativistic second harmonic generation from an S-polarized laser in over-dense plasma

A relativistic S-polarized short pulse laser impinged obliquely on an overdense plasma thin foil is shown to produce very significant second harmonic in the direction of specular reflection. The second harmonic is P-polarized and is driven by the second harmonic ponderomotive force on electrons in the skin layer. The treatment incorporates the electron density modification by the static ponderomotive force and mass modification due to relativistic effects. The second harmonic reflected amplitude is greatest for an optimum value of the angle of incidence. The conversion efficiency of the second harmonic is greater for higher values of incident laser amplitude and lower values of electron density in the foil. The equivalence between the total ponderomotive force and the radiation pressure force is also demonstrated.

An Accurate Exposure Time Measurement Method of CCD Cameras

In the shadow photograph system in ballistics range, the exposure time of the CCD cameras is a very important parameter. The method to measure the accurate exposure time of the CCD camera is suggested based on the short pulsed laser source, timing sequence control system, high speed photo- detector and oscilloscope with the precision of 0.1μs. This method solved the problem of no effective measurement method with high precision for this parameter. The accurate minimum exposure time of IGV-B4820 of company Imperx was tested by this method successfully.

Ultrafast All-Optical Switching with Transparent and Absorptive Nematic Liquid Crystals–Implications in Tunable Metamaterials

We present a critical review of the nonlinear optical responses of nematic liquid crystals associated with short pulsed laser induced thermal, density and order parameter fluctuations. Experimental studies conducted with absorbing as well as transparent nematic liquid crystals have demonstrated that all-optical one-way switching of nanoseconds pulsed laser at 750 nm can be realized at sub-microseconds to nanoseconds speed. Similar switching performances have also been observed with lasers at other visible–infrared regime, confirming the broadband applicability of the underlying nonlinear optical processes.

The shorter, the better

AbstractThe smaller the components, the shorter the pulse duration: particularly for manufacturing of medical implants the technological and economical advantages are obvious. Ultra short pulsed lasers are considered as only suitable tool for that kind of application. Meanwhile, additional industrial applications for femtosecond lasers arise (Fig. 1).

Laser focusing and multiple ionization of Ar in a hydrogen plasma channel created by a pre-pulse

AbstractA model for plasma channel formation by a laser pre-pulse in a low Z gas (Hydrogen) embedded with high Z atoms (Ar) is developed. The laser of intensity I ≅ 1014 W/cm2 ionizes hydrogen atoms fully whereas Ar atoms are ionized only singly. After the first pulse is gone, plasma expands on the time scale of a nanosecond to produce a hydrogen plasma channel with minimum density on the axis. A second intense short pulse laser of intensity I ≥ 1016 W/cm2 gets focused. It tunnel ionizes the remaining Ar. The Ar acquires Ar8+ charge state after loosing 8 ions and acquires Ne like configuration and could emit X-rays.

Comparative analysis of laser-triggered proton generation from overdense and low-density targets

Abstract Based on 3D particle-in-cell (PIC) simulations a comparative analysis of laser-triggered proton generation from the interaction of short high-intensity laser pulses with ultrathin foils and dense gas jets has been performed. It has been shown that for ultra-relativistic laser intensities the use of low-density targets with near critical density (aerogel or dense gas jet) has no advantage in comparison with ultrathin foils in terms of maximum proton energy and spectrum quality. Utilization of mass-limited foils with submicron thickness demonstrates even greater superiority for overdense targets and allows one to produce monoenergetic proton beams with energies of hundreds of mega-electron-volts by using high-contrast laser pulses with energies of the order of tens of Joules.

Improving Image Contrast of Fiber Point Diffraction Interferometer

To measure spherical surface with high precision, an advanced fiber point diffraction interferometer (FPDI) is introduced in this paper. Based on the system principle, the factors that affect the interference image contrast are put forward and analyzed, such as fiber optical properties, interferogram background and intensity match of two beams. Then the optimization method is proposed. The single-mode fiber with core diameter 3λ is selected and the dispersion between modes is removed. The short coherence length laser is designed with a semiconductor solid-state laser and meets the need of FPDI. By coating film on the fiber end face, the light use ratio is improved significantly. Finally, the fiber point diffraction interferometer system is set up in experiment and the interference fringes are obtained. The result shows that the FPDI can achieve interference patterns with high contrast after optimization and the system has reached a relatively high accuracy.

Simulation and Experiment of High-Speed Dynamic Plate Deformation Process Shocked by Pulsed Laser

The deformation process of plate material shocked by high-power short pulsed laser is one of the key problems for laser shock forming. In this paper, the finite element software ABAQUS is used to simulate the deformation process. A simple and novel optoelectronic measurement system is applied to measure the deformation process of aluminum sheet. The experiment and simulation results show that the load from the high-power short pulsed laser irradiation can be regard as transient pressure and the dynamic displacement law is damped oscillation.

Nonlinear Micro-Processing of Silicon by Ultrafast Fiber Laser at 1552 nm

ABSTRACTProcessing of transparent materials by non-linear absorption mechanisms induced by short pulse lasers has been applied in many fields. Silicon (Si) is widely used materials in microelectronics, MEMS and photonics. It is, however, not transparent for commonly used processing lasers in near infrared to ultraviolet spectral range and has not been a subject for the non-linear processing by lasers so far. In this paper, possibilities and capabilities of non-linear processing of Si by 900 fs, 1552nm laser radiation are described with special emphasis on application to frequency adjustment of a crystal oscillator in a package made from Si.

基于Bi3+Ga3+Al3+共掺高掺铒光纤的短线腔激光器

基于Bi³⁺Ga³⁺Al³⁺共掺高掺铒光纤的短线腔激光器

周期構造形成しきい値近傍領域における短パルスレーザー照射による金属材料の表面形状変化

周期構造形成しきい値近傍領域における短パルスレーザー照射による金属材料の表面形状変化