C. H. Tsou

Observation of self-mode-locking assisted by high-order transverse modes in optically pumped semiconductor lasers

The criterion for achieving the self-mode-locking (SML) in an optically pumped semiconductor laser (OPSL) with a linear cavity is systematically explored. Experimental results reveal that the occurrence of SML can be assisted by the existence of high-order transverse modes. Numerical analysis is performed to confirm that the critical pump power for obtaining the SML operation agrees very well with the pump threshold for exciting TEM1,0 mode. The present finding offers an important insight into laser physics and a useful indication for obtaining the SML operation in OPSLs.

A high-power harmonically self-mode-locked Nd:YVO 4 1.34- m laser with repetition rate up to 32.1 GHz

We develop a practical method to achieve harmonically self-mode-locked operation in a Nd:YVO4 1.34- m laser for the generation of high-repetition-rate pulse trains. We exploit a gain medium with partial-reflection coating at the lasing wavelength to introduce effective mode selection. We numerically demonstrate that the coated gain medium can effectively modify the mode spacing of the laser cavity to be the harmonics of the free spectral range of the gain medium when the optical cavity length is adjusted to be commensurate with the optical length of the gain medium. We further employ a coated Nd:YVO4 crystal to realize harmonically mode-locked operation with a highest repetition rate of up to 32.1 GHz. At a pump power of 11.5 W, the average output power of 2.3 W is generated with a pulse duration as short as 5.7 ps. The locking range for the cavity length is also experimentally explored.

Exploring the influence of high order transverse modes on the temporal dynamics in an optically pumped mode-locked semiconductor disk laser

We quantitatively investigate the influence of high-order transverse modes on the self-mode locking (SML) in an optically pumped semiconductor laser (OPSL) with a nearly hemispherical cavity. A physical aperture is inserted into the cavity to manipulate the excitation of high-order transverse modes. Experimental measurements reveal that the laser is operated in a well-behaved SML state with the existence of the TEM(0,0) mode and the first high-order transverse mode. While more high-order transverse modes are excited, it is found that the pulse train is modulated by more beating frequencies of transverse modes. The temporal behavior becomes the random dynamics when too many high-order transverse modes are excited. We observe that the temporal trace exhibits an intermittent mode-locked state in the absence of high-order transverse modes.

High-peak-power optically-pumped AlGaInAs eye-safe laser with a silicon wafer as an output coupler: comparison between the stack cavity and the separate cavity

An intrinsic silicon wafer is exploited as an output coupler to develop a high-peak-power optically-pumped AlGaInAs laser at 1.52 μm. The gain chip is sandwiched with the diamond heat spreader and the silicon wafer to a stack cavity. It is experimentally confirmed that not only the output stability but also the conversion efficiency are considerably enhanced in comparison with the separate cavity in which the silicon wafer is separated from other components. The average output power obtained with the stack cavity was 2.02 W under 11.5 W average pump power, corresponding to an overall optical-to-optical efficiency of 17.5%; the slope efficiency was 18.6%. The laser operated at 100 kHz repetition rate and the pulse peak power was 0.4 kW.

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.

Various phenomena of self-mode-locked operation in optically pumped semiconductor lasers

This work presents several optical experiments to investigate the phenomenon of self-mode locking (SML) in optically pumped semiconductor lasers (OPSLs). First of all, we systematically explore the influence of high-order transverse modes on the SML in an OPSL with a linear cavity. Experimental results reveal that the occurrence of SML can be assisted by the existence of the first high-order transverse mode, and the laser is operated in a well-behaved SML state with the existence of the TEM0,0 mode and the first high-order transverse mode. While more high-order transverse modes are excited, it is found that the pulse train is modulated by more beating frequencies of transverse modes. The temporal behavior becomes the random dynamics when too many high-order transverse modes are excited. We observe that the temporal trace exhibits an intermittent mode-locked state in the absence of high-order transverse modes. In addition to typical mode-locked pulses, we originally observe an intriguing phenomenon of SML in an OPSL related to the formation of bright-dark pulse pairs. We experimentally demonstrated that under the influence of the tiny reflection feedback, the phase locking between lasing longitudinal modes can be assisted to form bright-dark pulse pairs in the scale of round-trip time. A theoretical model based on the multiple reflections in a phase-locked multi-longitudinal-mode laser is developed to confirm the formation of bright-dark pulse pairs.

Observation of reflection feedback induced the formation of bright-dark pulse pairs in an optically pumped semiconductor laser.

It is experimentally demonstrated that the tiny reflection feedback can lead the optically pumped semiconductor laser (OPSL) to be operated in a self-mod-locked state with a pulse train of bright-dark pulse pairs. A theoretical model based on the multiple reflections in a phase-locked multi-longitudinal-mode laser is developed to confirm the formation of bright-dark pulse pairs. The present finding can offer an important insight into the temporal dynamics in mode-locked OPSLs.

Nondiffracting superlattice beams

We introduce a class of optical superlattices that are formed by two sets of wave vectors with single wave number but different azimuths. By a collimated light to illuminate a mask with multiple apertures, we generate nondiffracting superlattice beams.

Exploring optical properties of Nd-doped vanadates with intracavity self-mode locking

We employ an intracavity self-mode-locked laser to systematically measure the group refractive indices and the thermo-optic coefficients for Nd:GdVO4, Nd:YVO4 and Nd:LuVO4 crystals at 1064 nm. We further make a detailed comparison between the present results and those currently reported in the literature. All the experimental results can be found to be fairly consistent with the recent reported data

Formation and recurrence of quasicrystalline patterns from quantum dynamics of suddenly released matter waves: Analogous manifestation of optical waves

We analytically and numerically verify that two-dimensional (2D) quasicrystalline matter waves can be formed from the free-time evolution of multiple Gaussian waves regularly distributed on a circular ring. We also demonstrate that an interesting recurrence phenomenon can be manifested by adding an extra Gaussian wave on the center of multiple Gaussian waves uniformly distributed on a ring. We finally employ an optical experiment for the coherent light passing through the mask to analogously illustrate the formation of 2D quasicrystalline patterns and the associated recurrence.