Super continuum generation in water doped with Homeopathic medicines

We have carried out systematic studies to investigate the effect on supercontinuum generation in water using 40 fs laser pulses when doped with Homeopathic medicines. We perform these studies using five series of medications with different levels of dilution (10-30 to 10-100000). We measure supercontinuum spectra that span from 400-1050 nm. We monitor the area under the curve in the range 450-750 nm for each sample at a fixed incident laser energy. Our observations indicate that the yield of supercontinuum generation, in water containing Homeopathic medicine is significantly different from that obtained in water containing plain ethanol. The measurement for different dilutions shows up to 7 times standard deviation variation in the yield of supercontinuum generation? Even though linear absorption in the UV-visible region does not show any significant difference for different Homeopathic medicines, the supercontinuum yield which depends on the effective nonlinear refractive index changes with different samples.

Optically-excited simultaneous photoacoustic and ultrasound imaging based on a flexible gold-PDMS film

We constructed a flexible gold-polydimethylsiloxane (gold-PDMS) nanocomposites film with controllable thickness and light transmittance, to realize optically-excited simultaneous photoacoustic (PA) and ultrasound (US) imaging under a single laser pulse irradiation. Benefiting from the excellent thermoelastic properties, the gold-PDMS film absorbs part of the incident laser energy and produces a high-intensity US, which is used to realize US imaging. Meanwhile, the partly transmitted light is used to excite samples for PA imaging. By controlling the thickness of the gold-PDMS, we can control the center frequency in the US imaging. We experimentally analyzed the frequency of the produced US signal by the gold-PDMS film and compared it with the finite element analysis (FEA) method, where the experiments agree with the FEA results. This method is demonstrated by the experiments on phantoms and a mouse model. Our work provides a cost-effective methodology for simultaneous PA and US imaging.

Numerical modeling of quantum beam generation from ultra-intense laser-matter interactions

When intense laser beams interact with solid targets, high-energy photons are effectively generated via radiation reaction effect. These photons receive a large portion of the incident laser energy, and the energy transport by photons through the target is crucial for the understanding of the laser–matter interactions. In order to understand the energy transport, we newly developed a Particle-in-Cell code which includes the photon–matter interactions by introducing photon macro-particles. Test simulations are performed and compared with simulations using a particle transport code, which shows a good agreement.

Shadowgraph of Pulse CO2 Laser Induced Breakdown in Different Pressure Air

The expansion property of an infrared CO2 laser produced air plasma is characterized using a high-speed imaging shadowgraph technique. The shadowgraphs were taken by a time-gated intensified charge-coupled device at various delay times after single pulses induced gas breakdown. We examined five incident laser energy of 180, 240, 345, 420 and 600 mJ induced air breakdown at the pressure of atmospheric and 104 Pa. A shock wave produced by laser induced breakdown was also observed and its speed was measured as a function delay time between the breakdown and the shadow imaging under different air pressure. The experimental results indicated that the radial and axial shock wave front evolutions showed similar behavior, which increased fast with delay time at early stage and slowly at later stage. The propagation speed of the wavefront was about 2 cm/μs at the initial stage of breakdown, and then decreased very quickly. The propagation speed under low air pressure was higher than that of gases under high pressure and the spark sustained less time at lower pressure. The size of laser induced air spark increased with incident laser energy but not simple linear relationships.

Research of the Reactivity Photoacoustic Characteristics of PETN and HNS Induced by Laser

The reactivity photoacoustic technology was used to detect the laser induced photoacoustic spectroscopy characteristics of explosives (PETN and HNS). The results showed that: the reflectivity of pure PETN and HNS under laser irradiation was large and the photoacoustic signal was weak. After doping with carbon nanotubes (CNTs) and carbon black (CB), the reflectivity decreased. The photothermal conversion and the optical absorption coefficient rate increased and the photoacoustic signal enhanced. For the same sample, the intensity of the signal was proportional to the incident laser energy. For the same explosives and under the same doping amount, the photoacoustic signal of the CNTs doped sample is greater than that of the CB doped sample. For the same sample and the same dopant, the greater the amount of doping, the stronger the photoacoustic signal. There was optimum ignition energy. By using TG-DSC technology for thermal analysis of the samples, the results from the thermal analysis could explain the reactivity photoacoustic experiment.

Selective Laser Melting of Low-Modulus Biomedical Ti-24Nb-4Zr-8Sn Alloy: Effect of Laser Point Distance

As many complex processing parameters are involved in Selective Laser Melting (SLM), an understanding of the scientific and technical aspects of the production route on the microstructural evolution during SLM process is required in order to obtain parts with near full density and desirable surface finish. Although the effects of the various processing parameters on the density of parts have been well documented, the effect of laser point distance on density and mechanical properties of the SLM-produced parts has not been widely studied. In this paper, we present the results of using SLM to produce biomedical beta Ti-24Nb-4Zr-8Sn components. Both the density and hardness of the material increases with increasing incident laser energy and reaches a near full density value of >99% without any post-processing. When the laser energy density input is high enough to fully melt powder, the laser point distance has no influence on the density or hardness of the samples. In contrast, at low energy densities, large point distances have been shown to be detrimental.

Raman Spectroscopy on Individual Identified Carbon Nanotubes

ABSTRACTIn this paper, we discuss the low-frequency range of the Raman spectrum of individual suspended index-identified single-walled (SWCNTs) and double-walled carbon nanotubes (DWCNTs). In SWCNTs, the role of environment on the radial breathing mode (RBM) frequency is discussed. We show that the interaction between the surrounding air and the nanotube does not induce a RBM upshift. In several DWCNTs, we evidence that the low-frequency modes cannot be connected to the RBM of each related layer. We discuss this result in terms of mechanical coupling between the layers which results in collective radial breathing-like modes. The mechanical coupling qualitatively explains the observation of Raman lines of radial breathing-like modes, whenever only one of the layers is in resonance with the incident laser energy.

Angular Distribution and Ion Time of Flight Produced on Silicon Target by Laser Irradiation

The growth of thin films by laser ablation involves very complex physical processes. The quality of the layer and stoechiometry of the deposits depend on key parameters like the ion energy and their angular distribution. The evolution of ions number and energy, and the angular distributions in regards to the incident laser energy, have been studied by the mean of a charges collector. We present the polar diagrams of energy and number of ions collected by irradiating a silicon target using an excimer laser at different energies.