Table of contents

We demonstrated the laser performance of an Yb:YAG/YAG composite ceramic laser medium mounted on an aluminium heatsink via atomic diffusion bonding (ADB) technique using nanocrystalline metal films at room temperature in air. The surface temperature rise of the ADB bonded laser medium was linear with 57 °C lower than that of the commercially available soldered Yb:YAG thin disk at the pump power of 280 W. Moreover, the ADB disk was pumped 1.5 times higher (7.3 kW cm⁻²) than the typical damage threshold of the soldered disk without any sign of damage. The undoped capping may be effective for the suppression of ASE heating; however, according to the in situ OPD measurement it induces strong thermal lensing. The CW laser output power of 177 W was obtained at the pump power of 450 W with the optical-to-optical efficiency of 40% using V-shape cavity.

A laser oscillator based on Ho:YAG crystal pumped by a Tm fiber laser with an acousto-optical Q-switch was optimized for maximum output power and pulse-to-pulse stability. Stable operation at 2097 nm in Q-switched mode is demonstrated, with pulse repetition rates from 10 to 30 kHz, and output power of 36 W (at 55 W of pump power at 1908 nm) in the good quality beam. The influence of Ho ion up-conversion and thermal lensing on the oscillation efficiency is discussed.

The feasibility of constructing a compact, all-fiber, dissipative soliton resonance (DSR) mode-locked erbium–ytterbium double clad laser emitting 6.517 µJ pulses directly from the cavity is presented. The laser was built in a figure-8 configuration and mode-locked using a nonlinear optical loop mirror. A DSR regime of operation was enforced in the cavity by large net-anomalous dispersion (−21.431 ps²), obtained by incorporating 1 km of SMF28 fiber in the resonator. The laser operated at a 201 kHz repetition rate, with maximum average output power of 1.31 W at 7.2 W of pump power, yielding an impressive 20% slope efficiency.

Experimental observation of long-term output mode shape degradation in pulsed Yb-doped fiber amplifiers is reported for the first time. The process occurs in large mode area Yb-doped fibers and is caused by the formation of the long period grating responsible for power transfer from the fundamental mode to the first high-order mode. The linkage between the process and photodarkening was revealed.

A novel method of simultaneous distributed temperature and strain sensing in optical fibers is proposed. The method is based on the dependence of spontaneous Raman scattering intensity on the applied stress. A simple Raman reflectometry arrangement similar to distributed temperature sensors is used. 30 µ strain and 0.02 K root mean square errors of the simultaneously measured strain and temperature, respectively, are demonstrated for a spatial resolution of 2 m. Realization through this method is simple and can compete with the one based on Brillouin scattering for some applications.

Nonlinear optical coupling between two single-mode fibers terminated coaxially in a nematic liquid crystal (NLC) was explored for the first time. Light-induced reorientation of nematic molecules can result in the stable self-collimation of light transmitted through the gap between fibers. Thus, high coupling efficiency can be achieved despite large fiber spacing. We demonstrated a coupling efficiency of up to ∼0.7, achieved with spacing equal to four diffraction lengths. This feature opens up possibilities for the development of novel in-line fiber-optic elements based on NLCs. For instance, a polarization controller was proposed and considered.

Imaging through atmospheric turbulence is a topic with a long history and grand challenges still exist in the remote sensing and astro observation fields. In this letter, we try to propose a simple scheme to improve the resolution of imaging through turbulence based on the computational ghost imaging (CGI) and computational ghost diffraction (CGD) setup via the laser beam shaping techniques. A unified theory of CGI and CGD through turbulence with the multi-Gaussian shaped incoherent source is developed, and numerical examples are given to see clearly the effects of the system parameters to CGI and CGD. Our results show that the atmospheric effect to the CGI and CGD system is closely related to the propagation distance between the source and the object. In addition, by properly increasing the beam order of the multi-Gaussian source, we can improve the resolution of CGI and CGD through turbulence relative to the commonly used Gaussian source. Therefore our results may find applications in remote sensing and astro observation.

We demonstrate that a photon echo can be implemented by all-optical means using an array of on-chip high-finesse ring cavities whose parameters are chirped in such a way as to support equidistant spectra of cavity modes. When launched into such a system, a classical or quantum optical signal—even a single-photon field—becomes distributed between individual cavities, giving rise to prominent coherence echo revivals at well-defined delay times, controlled by the chirp of cavity parameters. This effect enables long storage times for high-throughput broadband optical delay and quantum memory.

The phenomenon of multiple rescatterings in the process of high-order harmonic generation from a helium atom with a long wavelength is investigated by solving the time-dependent Schrödinger equation and the classical equation of motion. The results present the rule of cutoff energies for the multirescattering events. What is more, the physical picture of the multiple rescatterings is built and the physical mechanism is revealed in detail. Further studies show that the multiple rescatterings can be manipulated effectively and the intra-cycle interference of multiple rescatterings is weakened simultaneously when the initial state is prepared in the superposition state. Additionally, the long quantum path is verified to play an important role in the multiple rescattering processes.

Evidence is found for a decrease of the Raman shift in stimulated Raman scattering with an increase of the pump intensity, which is interpreted as a manifestation of vibrations' nonisochronism. It is shown that the nonisochronism corresponds to a saturation-type nonlinearity of material vibrations in fused silica and to a Kerr-like nonlinearity in BK-7 glass.

We examine the influence of the structural self-similarity of the kagome lattice on the defect modes and waveguiding properties of hollow-core kagome-cladding fibers. We show that the guidance of such fibers is influenced by photonic band gaps (PBGs) which appear for a subset of the kagome lattice. Using these insights, we provide design considerations to further decrease loss in kagome-clad fibers.

Tumor oxygenation and hemoglobin content are the key indicators of the tumor status which can be efficiently employed for prognosis of tumor development and choice of treatment strategy. We report on monitoring of these parameters in SKBR-3 (human breast adenocarcinoma) tumors established as subcutaneous tumor xenografts in athymic nude mice by diffuse optical spectroscopy (DOS). A simple continuous wave fiber probe DOS system is employed. Optical properties extraction approach is based on diffusion approximation. Statistically significant difference between measured values of normal tissue and tumor are demonstrated. Hemoglobin content in tumor increases from 7.0  ±  4.2 μM to 30.1  ±  16.1 μM with tumor growth from 150  ±  80 mm³ to 1300  ±  650 mm³ which is determined by gradual increase of deoxyhemoglobin content while measured oxyhemoglobin content does not demonstrate any statistically significant variations. Oxygenation in tumor falls quickly from 52.8  ±  24.7% to 20.2  ±  4.8% preceding acceleration of tumor growth. Statistical analysis indicated dependence of oxy-, deoxy- and total hemoglobin on tumor volume (p  <  0.01). DOS measurements of oxygen saturation are in agreement with independent measurements of oxygen partial pressure by polarography (Pearson's correlation coefficient equals 0.8).

The collision-induced stimulated photon echo formed on the broad spectral line on the transition with the angular momentum change ${{J}_{a}}=0\to {{J}_{b}}=1$ is studied theoretically. The dependencies of the echo intensity on the areas of exciting pulses and on the strength of the external magnetic field under the conditions of experiments in ytterbium (¹⁷⁴Yb) vapor are obtained. The ways to measure orientation and alignment relaxation rates of the excited atomic level are discussed.