Gyu Ug Kim

Transverse mode competition in gain-guided index antiguided fiber lasers

Single-mode laser action has been reported previously in a gain-guided, index antiguided fiber using a scalable side pumping scheme. In this paper we demonstrate the role of transverse mode competition on laser oscillation in such a fiber laser. It enables single, lowest-order mode lasing with a beam quality of M2<2 when using a combination of large fiber core radius and low output coupler reflectivity previously considered to rule out gain-guided index antiguided lasing with such beam quality. In addition, the larger core radii fibers and low output coupler reflectivity enables improved slope efficiency. Both theoretical analysis and experimental results are presented demonstrating mode competition governed lasing in a gain-guided, index antiguided fiber.

Transition from phase synchronization to complete synchronization in mutually coupled nonidentical Nd:YAG lasers

Using mutually coupled nonidentical continuous-wave Nd:YAG lasers, we experimentally confirmed the recently proposed transition route from phase synchronization to complete synchronization. As evidence of this transition we obtained the probability distribution of the intermittent synchronization time near the threshold of the complete synchronization transition.

Measurement of subpicosecond ultraviolet pulse widths by using the high-order nonlinear processes in a supersonic gas jet

Intensity correlation methods for measuring ultrashort UV pulse widths have been developed that employ, for the first time to our knowledge, third- and fifth-harmonic generation as well as four-photon ionization in a pulsed supersonic rare-gas beam; the methods are applicable to the whole UV range. The pulse width from a subpicosecond XeCl (308-nm) excimer laser system was reliably measured to be ∼360 fs.

Phase synchronization of chaotic lasers

We experimentally investigate phase synchronization between two electronically coupled diode laser pumped Nd:YAG lasers. As the coupling strength increases, the phase of the two chaotic laser outputs develops from a nonsynchronous state to a phase synchronous one through a phase jump state. We find that there are 2pi phase jumps and a pi/2 phase shift between the two laser outputs unlike in optically coupled Nd:YAG lasers. To clarify the transition to phase synchronization with a pi/2 phase shift, we analyze the phenomenon of phase synchronization by using a phase portrait, phase difference dynamics, and frequency variation depending on the coupling strength and obtain the scaling rule of the average phase locking time in the intermittent phase jump state.

Diode Side Pumping of a Gain Guided, Index Anti-Guided Large Mode Area Neodymium Fiber Laser

Diode side pumping of a gain guided, index anti-guided neodymium doped fiber laser is demonstrated. This method of pumping may lead to a scalable approach to create high power, extremely large mode area fiber lasers.

Observation and investigation of off-axis modes in a high-power Nd:YAG laser

Unusual transverse patterns were observed in a cw-lamp-pumped Nd:YAG laser near the boundaries of the stability zones of the laser resonator. An interpretation of these patterns is given in terms of off-axis modes, which can be excited owing to spherical aberrations and astigmatism of the thermal lens and thermally induced birefringence. Additional evidence of the off-axis character of the observed modes was obtained by analysis of the temporal behavior of the observed patterns.

Transition through on–off intermittency in Nd:YAG laser systems pumped by laser diodes

We have investigated the transition route in a gain-modulated intracavity frequency-doubled Nd:YAG laser pumped by a laser diode when a small gain is modulated periodically. Through analysis of the probability distribution and the scaling relationship as the parameters of a laser system are varied, we ascertained that the intermittent laser operation of the intracavity second harmonics is an on–off intermittency. This is what we believe is the first observation of the transition route in a gain-modulated laser system. As further evidence of this transition route, similar intermittent behaviors were obtained in an acousto-optically Q-switched Nd:YAG laser pumped by a laser diode.