High-power ytterbium-doped fibre master-oscillator power-amplifier at 1018 nm

A high-power master-oscillator power-amplifier (MOPA) at 1018 nm employing ytterbium (Yb)-doped fibres as a gain medium is reported. Utilizing a diffraction grating as a reflector, we could successfully suppress the influence of the broadband amplified spontaneous emission on the master-oscillator or the power-amplifier, resulting in stable amplification of the laser signal at 1018 nm. Based on a simple theoretical simulation on gain spectra and experimental investigation on parasitic lasing thresholds, the Yb fibre MOPA constructed in-house yielded 220 W of output at 1018 nm with a beam propagation factor (M2) of 1.1. The prospects for further power scaling are considered.

All-fiber all-normal-dispersion passively mode-locked neodymium-doped fiber laser operation at 1064 nm

In this work, we report an all-fiber Nd-doped passively mode-locked fiber laser based on nonlinear polarization rotation mechanism operating in the 1.06 μm region. When the pump power was 300 mW, a pulse with a maximum average output power of 0.63 mW, a narrowest pulse duration of 1.22 ps and a pulse repetition rate of 14.25 MHz was obtained.

Dynamical Casimir–Polder force in a semi-infinite rectangle waveguide

In this paper, we study the dynamical Casimir–Polder force between an ensemble of identical two-level atoms and the wall of a rectangle waveguide with semi-infinite length. With the presence of both the rotating wave and counter rotating wave terms in the light–matter interaction Hamiltonian, we utilize the perturbation theory to solve the Heisenberg equation. Up to the seconder of coupling strength, we obtain the energy shift analytically and the Casimir–Polder force numerically. Our result shows that the dynamical behavior of the Casimir force is closely connected to the photon propagation in the waveguide. Therefore, we hope this work will stimulate the studies about the quantum effect in waveguide scenario.

Fiber-optic vector acoustic receiver based on adaptive holographic interferometer

A mobile scalar–vector acoustic receiver is proposed, experimentally implemented and investigated. The key components of the receiver are (a) the six-channel fiber-optic coil-type sensor configured as to detect three projections of acoustic intensity vector, (b) the six-channel optical phase demodulator based on six-channel adaptive holographic interferometer configured with use of dynamic holograms multiplexed in a photorefractive crystal of cadmium telluride and (c) the signals recording ADC-based system combined with software package for data processing. Field tests of the developed receiver applied for obtaining scalar and vector parameters of acoustic waves generated by a stationary and moving acoustic source in open air and water area are carried out. Experimental results show perceptiveness of use of the fiber-optical adaptive interferometry system for bearing of weak acoustic sources in real conditions.

Spatio-temporal properties of pulse propagation in a graphene quantum system

In this paper we have theoretically studied the spatial-temporal evolution of electromagnetic light propagation through a four-level graphene quantum system by using density matrix method and perturbation theory. The four-level graphene quantum medium interacted by an elliptical polarized coupling and a weak probe lights, respectively. We present the analytical solution for solving the Maxwell–Bloch equations for graphene and electromagnetic field in space and time domains. Then, we have analyzed the dynamic control of pulse propagation and optical dual switching in such a laser-driven quantum system. Our theoretical findings show that by adjusting the optical parameters such as elliptical angle i.e. phase difference between right-and-left circularly polarized, one can easily control the absorption spectrum and pulse propagation of the probe light in graphene medium. Our results may have potential applications in designing the new quantum devices for usage in quantum information processing.

The effect of initial phase on the emission characteristics of forward electron colliding with a tightly focused linearly polarized few-cycle laser pulse

We have studied the high harmonic radiation property from the scattering of an electron with a focused few-cycle laser pulse by analyzing the distribution of the radiation field and the motion state of the electron. In the time domain, temporal width of the compressed radiation can reach 33 zs (zeptosecond), thus an ultrashort x-ray pulse was generated in the interaction process. The radiation in this process is vastly similar to high harmonic generation in the process of atomic strong-field. The latter depends to a large extent on the phase of carrier-envelope (CE) driving laser pulse. The cutoff of radiation spectrum can reach 1 × 10 5 ω 0 , and whether the high-order harmonic spectrum in the cut-off region can be well resolved depends on the CE phase. We have investigated the relationship between the maximum radiation intensity and the CE phase, and discussed a potential method to characterize the CE phase of an intense few-cycle laser pulse for broader application prospects.

Characterization of the palladium plasma produced by nanosecond pulsed 532 nm and 1064 nm wavelength lasers

Palladium plasma produced by nanosecond pulsed 532 nm and 1064 nm wavelengths lasers is studied with the help of planer Langmuir probe. The experiment is conducted over a wide range of the laser fluence (1.6–40 J cm−2). The measured time of flight ions distributions are used to infer total charge, kinetic energy of the palladium ions and plasma parameters. Our results indicate that the ion charge produced by both laser wavelengths is an increasing function of the laser fluence. Initially, the ion charge produced by 1064 nm is lower than 532 nm, but it increases at much faster rate with the rise of laser fluence as the inverse bremsstrahlung plasma heating prevails at higher plasma densities. The most probable kinetic energy of the Pd ions produced by 1064 nm wavelength is also lower than that of 532 nm. The time varying plasma electron temperature and electron density are derived from the current–voltage plots of the two plasmas. For both wavelengths, the electron temperature and electron density rapidly climb to a maximum value and then gradually decline with time. However, in case of the 532 nm, the electron temperature and electron density remain consistently high throughout the laser plasma. The results are compared the available literature and discussed by considering surface reflectivity, ablation rate of the Pd target and laser plasma heating. The results presented in this work will provide more insight into the process of laser ablation and can be useful for the development of laser-plasma ion sources.

Protecting the quantum state from a finite temperature decoherence source by parity-time symmetric operation

We examine the validity of the parity-time ( P T )-symmetric operation in protecting quantum state and entanglement in the non-zero temperature environment. Special attention is paid to the dependence of quantum fidelity and entanglement on the temperature. In particular, by solving the master equation, we get the exact analytical or numerical simulation expressions of the explicit formulas of protection, showing explicitly that P T -symmetric operation does indeed help in protecting quantum state from finite temperature decoherence.

LD-pumped high-power continuous-wave Pr3+:YLF deep red lasers at 718.5 and 720.8 nm

We demonstrated 22 W LD-pumped high-power continuous-wave (CW) deep red laser operations at 718.5 and 720.8 nm based on an a-cut Pr3+:YLF crystal. The output power of both polarized directions reached the watt-level without output power saturation. A single wavelength laser operated at 720.8 nm in the π-polarized direction was achieved, with a high output power of 4.5 W and high slope efficiency of approximately 41.5%. To the best of our knowledge, under LD-pumped conditions, the laser output power and slope efficiency are the highest at 721 nm. By using a compact optical glass plate as an intracavity etalon, we suppressed the π-polarized 720.8 nm laser emission. And σ-polarized single-wavelength laser emission at 718.5 nm was achieved, with a maximum output power of 1.45 W and a slope efficiency of approximately 17.8%. This is the first time that we have achieved the σ-polarized laser emission at 718.5 nm generated by Pr3+:YLF lasers.

Analytical calculation of the parameters of light bullets propagating in the tunnel ionization regime

Analytic estimation of the parameters of light bullets formed in the anomalous group dispersion region of transparent dielectrics under conditions of tunneling photoionization was performed. For this purpose, the system of the ordinary differential equations for the laser pulse’s parameters such as amplitude, temporal duration, chirp parameter, temporal delay, frequency shift, radius and curvature were obtained. The stationary solution of this system and conditions of the quasi-stable regime of propagation were found.