J. C. Tung

Exploring the spatio-temporal dynamics of an optically pumped semiconductor laser with intracavity second harmonic generation

We experimentally observe an intriguing phenomenon of complex spatio-temporal dynamics in a commercial optically pumped semiconductor laser with intracavity second harmonic generation. We numerically verify that the experimental results come from the total mode locking of transverse electromagnetic modes (TEM00) and higher-order modes with significant astigmatism. The scenarios of the spatio-temporal dynamics are quite similar to the phenomena in soft-aperture Kerr-lens mode locked Ti:sapphire lasers.

Spontaneous subpicosecond pulse formation with pulse repetition rate of 80 GHz in a diode-pumped Nd:SrGdGa 3 O 7 disordered crystal laser

We explore the operation of spontaneous mode locking in a diode-pumped Nd:SrGdGa3O7 disordered crystal laser. The first- and second-order autocorrelations are simultaneously performed to evaluate the temporal characteristics. An 80 GHz pulse train with a pulse duration as short as 616 fs is observed. The maximum output power is 415 mW at a pump power of 6.1 W.

Resolving the formation of modern Chladni figures

The resonant spectrum of a thin plate driven with a mechanical oscillator is precisely measured to distinguish modern Chladni figures (CFs) observed at the resonant frequencies from classical CFs observed at the non-resonant frequencies. Experimental results reveal that modern CFs generally display an important characteristic of avoided crossings of nodal lines, whereas the nodal lines of classical CFs form a regular grid. The formation of modern CFs and the resonant frequency spectrum are resolved with a theoretical model that characterizes the interaction between the plate and the driving source into the inhomogeneous Kirchhoff-Love equation. The derived formula for determining resonant frequencies is shown to be exactly identical to the meromorphic function given in singular billiards that deals with the coupling strength on the transition between integrable and chaotic features. The good agreement between experimental results and theoretical predictions verifies the significant role of the strong-coupling effect in the formation of modern CFs. More importantly, it is confirmed that the apparatus for generating modern CFs can be developed to serve as an expedient system for exploring the nodal domains of chaotic wave functions as well as the physics of the strong coupling with a point scatterer.

Power scale-up and propagation evolution of structured laser beams concentrated on 3D Lissajous parametric surfaces

We systematically explore the power scale-up and propagation evolution of Lissajous structured beams in a lowly Nd-doped YVO4 laser with the off-axis pumping scheme. We experimentally found that the average output power can be up to 1.0 W for the output transmission in the range of 1.8–10% at an incident pump power of 6.2 W. It is also found that when the output transmission is greater than 5%, the spatial coherence is considerably reduced to lead to a feature of broken Lissajous figures in transverse patterns. Moreover, transverse patterns varying with propagation direction are remarkably measured to manifest the 3D characteristics of Lissajous structured beams. We also employ the formula of coherent states to make a comparison with experimental observations and to reveal the transverse momentum density varying with propagation direction.

Precise measurement of the thermo-optical coefficients of various Nd-doped vanadates with an intracavity self-mode-locked scheme

We employ an intracavity self-mode-locked laser to precisely measure the group refractive indices and thermo-optic coefficients for Nd-doped vanadates at 1064 nm. The samples include Nd:GdVO4, Nd:YVO4 and Nd:LuVO4 crystals. We make a detailed comparison between the present results and those currently reported in the literature. We confirm that the present results are in good agreement with the currently available data with the best precision.

Exploring vortex structures in orbital-angular-momentum beams generated from planar geometric modes with a mode converter.

It is theoretically demonstrated that the planar geometric mode with a π/2 mode converter, so called the circularly geometric mode, can be solved from the inhomogeneous Helmholtz equation by considering the pump distribution on the lasing mode. Theoretical analysis clearly reveal that the vortex structures of circularly geometric modes are determined by the minimum order of transverse lasing modes, the total number of transverse lasing modes and the degenerate condition in the cavity. Moreover, we experimentally manifest that the circularly geometric mode can be generated from the selective pumped solid-state laser with an external π/2 mode converter. To explore the vortex structures of the generated geometric modes, the interference patterns are performed by an experimental apparatus consisting of a Mach-Zehnder interferometer. The good agreement between experimental observations and numerical calculations confirms the analysis of vortex structures is reliable.

Selective pumping and spatial hole burning for generation of photon wave packets with ray-wave duality in solid-state lasers

The selective pumping and the spatial hole burning are thoroughly considered to determine the excited transverse and longitudinal eigenmodes. By using the mode locking of the excited eigenmodes, an analytical wave representation is derived to manifest the ray-wave duality of the optical wave packet dynamics in the laser resonator. The derived wave function is employed to extract the parametric formula for the periodic ray orbits that reveal the subtle origin between the hyperbolic caustics and linear trajectories. Moreover, the temporal dynamics of the output beam for the total mode-locked state is theoretically demonstrated by combining with the parametric formula and the derived wave function. More importantly, an experiment based on the self-mode-locked laser is performed to make a comparison with theoretical analysis.

Manifesting the evolution of eigenstates from quantum billiards to singular billiards in the strongly coupled limit with a truncated basis by using RLC networks.

The coupling interaction between the driving source and the RLC network is explored and characterized as the effective impedance. The mathematical form of the derived effective impedance is verified to be identical to the meromorphic function of the singular billiards with a truncated basis. By using the derived impedance function, the resonant modes of the RLC network can be divided into the open-circuit and short-circuit states to manifest the evolution of eigenvalues and eigenstates from closed quantum billiards to the singular billiards with a truncated basis in the strongly coupled limit. The substantial differences of the wave patterns between the uncoupled and strongly coupled eigenmodes in the two-dimensional wave systems can be clearly revealed with the RLC network. Finally, the short-circuit resonant states are exploited to confirm that the experimental Chladni nodal-line patterns in the vibrating plate are the resonant modes subject to the strong coupling between the oscillation system and the driving source.

Generation of pseudonondiffracting optical beams with superlattice structures

We demonstrate an approach to generate a class of pseudonondiffracting optical beams with the transverse shapes related to the superlattice structures. For constructing the superlattice waves, we consider a coherent superposition of two identical lattice waves with a specific relative angle in the azimuthal direction. We theoretically derive the general conditions of the relative angles for superlattice waves. In the experiment, a mask with multiple apertures which fulfill the conditions for superlattice structures is utilized to generate the pseudonondiffracting superlattice beams. With the analytical wave functions and experimental patterns, the pseudonondiffracting optical beams with a variety of structures can be generated systematically.

Manifesting the connection between topological structures of quantum stationary coherent states and bundles of classical Lissajous orbits

Quantum stationary coherent states with spatial intensities localized on Lissajous orbits are theoretically explored by taking the inverse Fourier transform of the time-dependent coherent state. It is analytically verified that the stationary coherent state can be expressed as an integral of the Gaussian wave packet over the classical periodic orbit. With the derived integral, the phase singularities of the stationary coherent state can be precisely manifested from low-order to extremely high-order states. It is found that the phase singularities near the cross-point of the Lissajous orbits are generally arranged as rhombic vortex arrays. Finally, the stationary coherent states can be used as a basis to manifest the connection between topological structures of quantum eigenstates and bundles of classical Lissajous orbits.