We report the generation of 200kW-peak-power coherent radiation at 53 microns from a Raman-suppressed stimulatedpolariton- scattering laser using a thin KTP gain crystal at room temperature. The far-infrared radiation consists of ~500 radiation cycles in an 83-ps pulse width. Such a far-infrared source has a comparable or higher peak power than a nominal THz free-electron laser.
We report a continuous-wave, watt-level, red, green, and blue (RGB) laser pumped by a multi-longitudinal-mode Ybfiber
laser at 1064 nm. A singly resonant optical parametric oscillator at 1.56 μm has two intracavity sum-frequency
generators for red and blue laser generation. An extracavity second harmonic generator converts the residual pump
power into green laser radiation. At 25-W pump power, the laser generated 3.9, 0.46, and 0.49 W at 633, 532, and 450
nm, respectively. By replacing the multi-mode pump laser with a single-frequency one, we further increased the output
power of the green laser to 2 W.
Some believes that the useful length of THz different frequency generation (DFG) in a highly absorptive material is
comparable to the absorption length of the THz wave. We show in theory and experiment that it is only true for
backward THz DFG. For forward DFG with strong idler absorption, the THz wave can continue to grow with the length
of a DFG crystal.
The mechanisms of learning and memory are the most important functions in an animal brain. Investigating neuron
circuits and network maps in a brain is the first step toward understanding memory and learning behavior. Since
Drosophila brain is the major model for understanding brain functions, we measure the florescence lifetimes of different
GFP-based reporters expressed in a fly brain. In this work, two Gal4 drivers, OK 107 and MZ 19 were used.
Intracellular calcium ([Ca2+]) concentration is an importation indicator of neuronal activity. Therefore, several groups
have developed GFP-based calcium sensors, among which G-CaMP is the most popular and reliable. The fluorescence
intensity of G-CaMP will increase when it binds to calcium ion; however, individual variation from different animals
prevents quantitative research. In this work, we found that the florescence lifetime of G-CaMP will shrink from 1.8 ns to
1.0 ns when binding to Ca2+. This finding can potentially help us to understand the neuron circuits by fluorescence
lifetime imaging microscopy (FLIM). Channelrhodopsin-2 (ChR2) is a light-activated ion-channel protein on a neuron
cell membrane. In this work, we express ChR2 and G-CaMP in a fly brain. Using a pulsed 470-nm laser to activate the
neurons, we can also record the fluorescence lifetime changes in the structure. Hence, we can trace and manipulate a
specific circuit in this animal. This method provides more flexibility in brain research.
By using a novel temporal characterization technique, we determined that a threshold average laser power of 160 mW is required to drill through a 0.75-mm-thick cortical bone for a Nd:YVO4 mode-locked laser oscillator with a peak intensity of 1.3 GW/cm2. The ablation mechanism is identified as average-power induced carbonization followed by peak-power induced avalanche ionization in the carbonized osseous tissue.
We report simultaneous frequency conversion and amplitude modulation in an optical second harmonic generator by electro-optically controlling the relative phase between the 1064-nm fundamental and the 532-nm second harmonic fields in a dispersion crystal section between two periodically poled lithium niobate (PPLN) sections. Theoretical derivation and experimental demonstration were carried out for two novel crystal configurations, including a linear cascaded configuration in which a 1-cm dispersion section is sandwiched between two 2-cm PPLN sections, and a folding- crystal configuration in which the mixing waves traverse twice in a 2-cm PPLN section through total internal reflections in a 1.5-cm dispersion section. Due to the coherence enhancement in the constructive phase between the two SHG fields in the two PPLN sections, we measured a 30% increase in conversion efficiency compared to a continuous 4-cm PPLN under the same condition. The measured half-wave voltage for the amplitude modulation is 1.1 volt x d micrometers /ld(cm), where d is the separation of the electrodes and ld is the length of the electrodes.
We propose a dielectric-based, multistaged, laser-driven electron linear accelerometer microstructure operating in a vacuum that is capable of accelerating electrons to 1 TeV in one kilometer. Our study shows that a GeV/m gradient is achievable using two 100 fsec focused crossed-laser-beams, repeated every 300 micrometers , operated at a peak power of 0.2 GW and an energy density of less than 2J/cm2 on the accelerator structure.
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