Plasma-mediated ablation of biofilm contamination

Ultra-short pulsed laser removal of thin biofilm contamination on different substrates has been conducted via the use of plasma-mediated ablation. The biofilms were formed using sheep whole blood. The ablation was generated using a 1.2 ps ultra-short pulsed laser with wavelength centered at 1552 nm. The blood contamination was transformed into plasma and collected with a vacuum system. The single line ablation features have been measured. The ablation thresholds of blood contamination and bare substrates were determined. It is found that the ablation threshold of the blood contamination is lower than those of the beneath substrates including the glass slide, PDMS, and human dermal tissues. The ablation effects of different laser parameters (pulse overlap rate and pulse energy) were studied and ablation efficiency was measured. Proper ablation parameters were found to efficiently remove contamination with maximum efficiency and without damage to the substrate surface for the current laser system. Complete removal of blood contaminant from the glass substrate surface and freeze-dried dermis tissue surface was demonstrated by the USP laser ablation with repeated area scanning. No obvious thermal damage was found in the decontaminated glass and tissue samples.     

时变电流注入下光电负反馈垂直腔表面发射激光器的偏振双稳特性

基于光电负反馈垂直腔表面发射激光器(VCSELs)的理论模型,数值研究了时变电流注入下反馈率大小和注入电流扫描周期对VCSELs偏振双稳特性的影响.研究结果表明:增大反馈率将使双稳区域向更大电流方向移动,同时双稳区宽度增加;增大注入电流扫描周期将使双稳区宽度减小.因此,通过调整光电负反馈的大小以及注入电流的扫描周期,可实现对VCSELs偏振双稳特性的控制.     

外腔半导体激光器随机数熵源的腔长分析

利用光反馈半导体激光器产生的混沌激光作为随机数熵源,详细研究了混沌源外腔长度对500Mbit/s随机数特性的影响.研究表明:在单路混沌源情况下,外腔反馈引起的谐振会使产生的随机序列具有弱周期性,且当外腔反馈时间与采样时间的比值为整数时,产生序列的随机性最差,仅能通过NIST统计测试2,3项;在两路混沌源情况下,当混沌源的外腔长不相等且不成比例时,通过两路异或处理可消除由外腔反馈引起的弱周期性,产生的随机序列能够通过NIST的全部统计测试项.     

The progress towards terahertz quantum cascade lasers on silicon substrates

A review is presented of work over the last 10 years which has been aimed at trying to produce a Si‐based THz quantum cascade laser. Potential THz applications and present THz sources will be briefly discussed before the materials issues with the Si/SiGe system is discussed. Waveguide designs and waveguide losses will be presented. Experimental measurements of the non‐radiative lifetimes for intersubband transitions in Si_1‐xGe_x quantum wells will be presented along with theory explaining the important scattering mechanisms which determine the lifetimes. Examples of p‐type Si/SiGe quantum cascade designs with the experimental electroluminescence will be reviewed and examples of n‐type Si‐based designs will be presented. In the conclusion designs and structures will be discussed with the greatest potential to achieve an electrically pumped Si‐based THz laser.     

Blue‐green light generation using high brilliance edge emitting diode lasers

A review about second harmonic generation using edge emitting diode lasers and nonlinear crystals to obtain laser radiation in the blue‐green spectral range is presented. Therefore, pump laser radiation with high brightness and narrow bandwidth is necessary. Thus, this review gives an overview of the advances made with distributed feedback and Bragg reflector lasers, tapered lasers and amplifiers as well as external cavity diode lasers and master oscillator power amplifier schemes to achieve high brilliance emission. Since periodically poled materials have enabled high second harmonic conversion efficiencies with low and moderate pump powers, the review is focused on frequency doubling using those materials. The most commonly used materials, their properties and limitations are discussed briefly. Single pass and resonant SHG setups with waveguide and bulk nonlinear crystals are discussed and an emphasis on building compact and integrated devices is made.     

Design of wavelength adjustable lasers with photonic crystal based Fabry-Perot etalon for applications in optical network units of wavelength-division-multiplexed passive optical network systems

We propose a novel wavelength adjustable laser (WAL) with a photonic crystal based Fabry-Perot (FP) etalon. This laser will be a promising light source for optical network units (ONUs) of conventional wavelength-division-multiplexed passive optical network (WDM-PON) systems for up-stream transmission. It has the merits of a relatively simple fabrication and operation, wide process tolerance, low-cost, high side-mode suppression ratio, and wavelength-tunable characteristics. The optimization of the device structure and the implementation methods for this type of laser are discussed. Although the WALs in WDM-PON systems are not colorless, each laser can cover several wavelengths. Thus, the required number of different ONUs can be reduced. This approach may be necessary for 10 Gbps upstream transmission in next-generation optical access networks because the 10 Gbps data rate is difficult to achieve by using current colorless schemes.     

Plasma-based X-ray laser at 21 nm for multidisciplinary applications

An overview of recent advances in applications of currently the most energetic X-ray laser at 21 nm is given. The unique parameters of this half-cavity based X-ray laser such as record output energy of 10 mJ, highly symmetric beam, robustness and reproducibility, have made it possible to carry out a number of multidisciplinary scientific projects featuring novel applications of intense coherent X-ray radiation. Selected results obtained in these experiments are reviewed, including X-ray laser probing of dense plasmas, measurements of transmission of focused soft X-ray radiation at intensities of up to 10¹² W cm^-2, measurements of infrared laser ablation rates of thin foils, and ablative microstructuring of solids.     

Incorporate, switchable dual-wavelength fiber laser with Bragg gratings written in a polarization-maintaining erbium-doped fiber

A stable, incorporate and switchable dual-wavelength fiber laser with two fiber Bragg gratings written in a photosensitive and polarization-maintaining erbium-doped fiber directly, that is, without splices in the laser cavity, is proposed and demonstrated. Simultaneous dual-wavelength oscillation is achieved at room temperature with a wavelength spacing of 0.343 nm. The power fluctuation and wavelength shift of single-wavelength oscillations are measured to be less than 0.24 dB and 0.013 nm over 2 h. The wavelength switchability between single- and dual-wavelength oscillations is realized by altering the voltage upon the electrostrictive ceramic actuator.     

Numerical analysis of multi-wavelength cascaded Raman fiber lasers based on genetic algorithm

A novel numerical method is presented for the calculations of the coupled propagation equations in multi-wavelength Raman fiber lasers. By taking the advantages of genetic algorithm and shooting method, only a few of the best individuals at each generation are chosen to implement several shootings in order to accelerate theirs converging. The output characteristics of an all-fiber three-wavelength Raman fiber laser have been analyzed based on the proposed algorithm. Results show that the total output power linearly depends on the pump power with a slope efficiency of ∼51%. For the three output Stokes, the slope efficiencies of the longer wavelengths are larger than that of the shorter ones because the optical energy at the Stokes with shorter wavelengths allows for a transfer of optical power to the longer Stokes via stimulated Raman scattering. We also find that the total output power degrades by less than 10% by adjusting the output-coupler reflectivity and is insensitive to the variation of the Raman fiber length over a large range.