Table of contents

The use of trapped atomic ions in the field of quantum information processing is briefly reviewed. We summarize the basic mechanisms required for logic gates and the use of the gates in demonstrating simple algorithms. We discuss the potential of trapped ions to reach fault-tolerant error levels in a large-scale system, and highlight some of the problems that will be faced in achieving this goal. Possible near-term applications in applied and basic science, such as in metrology and quantum simulation, are briefly discussed.

Diode end-pumped continuous wave (CW) and passively Q-switched (PQS) laser performances of the mixed Nd:Gd_0.33Lu_0.33Y_0.33VO₄ crystal are investigated for the first time. At the pump power of 9 W, the highest output power is 3.66 W, with an optical conversion efficiency of 40.7% and a slope efficiency of 43.6%. For pulsed operation, the minimum pulse width of 9.2 ns with Cr⁴⁺:YAG as saturable absorber is attained with the repetition rate of 81.8 kHz, and the single pulse energy and peak power are estimated to be 9.78 J and 1.06 kW, respectively.

The room temperature continuous wave (CW) laser performance of a compact Yb:CaYAlO₄ (Yb:CYA) laser with near quantum limit slope efficiency is demonstrated. Pumped with a CW diode operating at 979 nm, the laser emitted a maximum CW output power of 2.3 W at 1050 nm. The corresponding slope efficiency was found to be 92% while the optical to optical conversion efficiency was 70%. The laser can also be continuously tuned from 1008 nm to 1063 nm using an intra-cavity SF 10 prism. The round trip cavity losses of Yb:CYA was 0.6% while the loss coefficient of the crystal was 0.01 cm^-1.

We reported a continuous-wave (CW) passively mode-locked Nd:Lu_0.5Y_0.5VO₄ laser at 1064 nm. A partially reflective semiconductor saturable absorber mirror was exploited in the Z-typed resonator. The Nd:Lu_0.5Y_0.5VO₄ laser generated CW mode-locked pulses with an average output power of 860 mW, a repetition rate of 53.7 MHz, and a pulse duration of 8.7 ps.

In this paper, the absorption and emission spectra of Nd:Y_2.5Gd_0.5Al₅O₁₂ (Nd:YGAG) crystal at room temperature have been studied. With a laser diode (LD) as the pumping source, the maximum 1.66 W continuous-wave (CW) laser output power has been obtained, with the optical-to-optical efficiency of 46.6% and the slope efficiency of 50.6%. For passively Q-switched operation, the shortest pulse width attained was 11.0 ns, with the pulse repetition rate of 32.0 kHz, with the peak power and pulse energy estimated to be 2.1 kW and 22.8 μJ, respectively.

A quasi-continuously pumped picosecond oscillator-amplifier laser system based on two identical 2.4% Nd:YAG slabs in a single bounce geometry was developed and investigated. The oscillator was passively mode locked by the multiple quantum well saturable absorber inserted into the resonator in transmission mode. Output train containing 7 pulses with total energy of 900 μJ was generated directly from the oscillator. Single pulse with energy of 75 μJ, duration of 113 ps and Gaussian spatial profile was cavity dumped from the resonator and amplified by the single pass amplifier to the energy of 830 μJ. Comparison with our previously reported data obtained with similar system based on Nd:GdVO₄ shows advantage of using highly doped Nd:YAG for generation of sub-millijoule pulses in one hundred picoseconds range, which might be interesting in many applications.

Sum-frequency mixing of an 808 nm broad area laser (BAL) with a build-in grating structure for spectral control and a 1064 nm solid-state laser is experimentally investigated. The spectrally improved 20 μm wide BAL can deliver up to 700 mW of output power with an M² of 1.4 and 5.3 in the fast and slow axis of the diode, respectively. The BAL output beam is single-passed through a periodically poled KTiOPO₄ (PPKTP) crystal placed in an intra-cavity beam waist of a 1064 nm Nd:YVO₄ laser, resulting in 100 mW of sum-frequency generated blue output power. This corresponds to a power conversion efficiency of 15%. The near diffraction limited blue output beam is measured to have an M² of 1.2 and 1.7 in the directions corresponding to the fast and slow axis of the BAL diode, respectively.

Medium power (0.3 – 8.0 W) 970 nm in wavelength laser irradiation of water with added Ag nanoparticles (in the form of Ag-albumin complexes) through 400 μm optical fiber stimulates self-organization of filaments of Ag nanoparticles for a few minutes. These filaments represent themselves long (up to 14 cm) liquid gradient fibers with unexpectedly thin (10 – 80 μm) core diameter. They are stable in the course of laser irradiation being destroyed after laser radiation off. Such effect of filaments of Ag nanoparticles self-organization is rationalized by the peculiarities of laser-induced hydrodynamic processes developed in water in presence of laser light and by formation of liquid fibers.

The effects of the longitudinal magnetic field on the collision photon echo, which is formed by two laser pulses with orthogonal polarizations on the transition with the angular momentum change J_a = 0 → J_b = 1 and arises due to the action of the elastic depolarizing collisions, are studied theoretically. It is shown that weak magnetic field acts to diminish the intensity of the collision echo up to zero, providing the tools for measuring the relaxation rates due to such collisions. With the further increase of the magnetic field strength the echo intensity reveals almost pure harmonic oscillations, though in strong magnetic field the echo appears not due to the action of collisions but mainly due to the action of the magnetic field, so it becomes not collision but conventional photon echo. However the comparison of the amplitudes of the collision echo in zero magnetic field with the maximum echo amplitude in strong magnetic field yields one more way to measure the relaxation rates due to elastic depolarizing collisions.

We show what we believe is the first demonstration of an ytterbium-doped strictly all-fiber active mode-locking laser. The active control of the laser is based on in-fiber amplitude modulation at 11 MHz, which is achieved by using an all-fiber acoustooptic superlattice modulator driven by standing acoustic waves. In our experiments, the laser was operated at 1091.3 nm and had two stable regimes producing either a train of mode-locked single pulses or a train of pulse pairs. Best results for the mode-locked train of single pulses were 740 ps of time width and 26 mW of average power, at a pump power of 480 mW.

Singlet oxygen (¹O₂) can be generated in a living cell upon focused laser irradiation of the intracellular photosensitizers. ¹O₂ lifetime in the living cells is shortened by the reactions with cellular molecules, and thus the ¹O₂ diffusion in a single cell has attracted much attention. In this study, ¹O₂ generation from the plasma membrane-targeted protoporphyrin IX (PpIX) and nuclear-targeted meso-Tetra (N-methyl-4-pyridyl) porphine tetra tosylate (TMPyP) in human nasopharyngeal carcinoma CNE2 cells was indirectly imaged by using a fluorescence probe Singlet Oxygen Sensor Green agent (SOSG), respectively. The confocal images indicate that the green fluorescence of SOSG in the vicinity of the PpIX-sensitized cells was dramatically enhanced with the increase of the irradiation time and intracellular PpIX, while there is no significant enhancement for the unsensitized and TMPyP-sensitized cells. The obtained results suggest that the ¹O₂ generated from the plasma membrane-targeted PpIX in the CNE2 cells can escape into the extracellular medium and react with the SOSG to produce SOSG endoperoxides (SOSG-EP). Moreover, the fluorescence enhancement of SOSG mainly depends on the subcellular localization and intracellular uptake of the photosensitizers. Depending on the site of ¹O₂ generation, ¹O₂ generated in the plasma membrane can escape from the cell interior into the extracellular environment, while the ¹O₂ generated in the nucleus cannot. Our findings indicate that SOSG holds great promise for the indirect imaging of the ¹O₂ that can escape from single intact living cells.

We present experimental evidence of the existence of cell variability in terms of threshold light dose for Hep G2 (liver cancer cells) cultured. Using a theoretical model to describe the effects caused by successive photodynamic therapy (PDT) sessions, and based on the consequences of a partial response we introduce the threshold dose distribution concept within a tumor. The experimental model consists in a stack of flasks, and simulates subsequent layers of a tissue exposed to PDT application. The result indicates that cells from the same culture could respond in different ways to similar PDT induced-damages. Moreover, the consequence is a partial killing of the cells submitted to PDT, and the death fraction decreased at each in vitro PDT session. To demonstrate the occurrence of cell population modification as a response to PDT, we constructed a simple theoretical model and assumed that the threshold dose distribution for a cell population of a tumor is represented by a modified Gaussian distribution.

Live imaging of normal and abnormal vascular development in mammalian embryos is important tool in embryonic research, which can potentially contribute to understanding, prevention and treatment of cardiovascular birth defects. Here, we used speckle variance analysis of swept source optical coherence tomography (OCT) data sets acquired from live mouse embryos to reconstruct the 3-D structure of the embryonic vasculature. Both Doppler OCT and speckle variance algorithms were used to reconstruct the vascular structure. The results demonstrates that speckle variance imaging provides more accurate representation of the vascular structure, as it is not sensitive to the blood flow direction, while the Doppler OCT imaging misses blood flow component perpendicular to the beam direction. These studies suggest that speckle variance imaging is a promising tool to study vascular development in cultured mouse embryos.