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Spectral behaviors of lasing from semiconductor square ring microcavities with structures for unidirectional laser oscillation were investigated. When a tapered structure was introduced, the lasing envelope shifted to a shorter wavelength region. Statistical estimate of the additional loss caused by the tapered structure was carried out by analyzing spectral data from many sets of cavities with various sizes. When a saw-edged structure was introduced, the unidirectional lasing functioned well but no apparent spectral shift was observed due to negligible additional loss.

Operation properties, such as output power, beam radius, and crystal temperature rise were investigated in a diode-pumped edge-cooled monolithic Yb:YAG laser with ~ 4 W pumping level. The output power showed saturation behavior because of severe temperature rise and poor spatial overlapping between pump beam and lasing mode. Face cooling geometry by using a sapphire plate was also investigated. No apparent saturation behavior in output power was observed due to the reduced temperature rise, which could be attributed to efficient heat removal through the crystal-sapphire interface.

The 1 kJ Nd:Glass laser at KAERI1 has symmetrically irradiated a SiO2 shell from tetrahedral direction for uniform compression of a spherical target since August 2015. A spherical target chamber with turning mirrors, focusing lenses and monitoring instrument was installed to generate a high density laser-plasma by irradiating four laser beams.

We numerically investigate the generation of wavelength-tunable few-cycle pulses in the visible spectral region through soliton-plasma interactions. We found that in a He-filled single-ring photonic crystal fiber (SR-PCF), soliton-plasma interactions could shift the optical spectra of pulses propagating in the fiber to shorter wavelengths. Through adjusting the single pulse energy launched into the fiber, the central wavelength of these blueshifting pulses could be continuously tuned over hundreds of nanometers, while maintaining a high energy conversion efficiency of >57%. Moreover, we observed that during the nonlinear pulse propagation in the SR-PCF, soliton self-compression effects enhanced the plasma density in the fiber at high pulse energies, which could modulate the phase-matching condition of ultraviolet (UV) dispersive wave (DW) generation. Furthermore, we employed the recently-developed model to study numerically the loss and dispersion of the SR-PCF in its resonant and anti-resonant spectral regions, and demonstrated the remarkable influence of the core-cladding resonance on the process of soliton-plasma interactions. The numerical results demonstrated here pave the way to develop wavelength-tunable, few-cycle light sources in the visible region, which may have considerable application potential in pump-probe spectroscopy and strong-field physics.

A temperature measurement scheme using spectral shift was applied to a diode end-pumped Yb:YAG laser with ∼ 4 W pumping level. The temperature rise was ∼ 90 °C at the input power of 3.3 W.

Laser isotope separation experiments of Gd and B by atomic and molecular methods, respectively, have been performed. Gadolinium-157 was selectively photoionized by means of three linearly polarized dye lasers, the excitation process of which is based on the polarization selection rules. The effect of magnetic field on isotopic selectivity was discussed. 10BCl3 was selectively photodissociated through IR multiphoton dissociation by the irradiation of TEA CO2 laser or free electron laser (FEL). Selectivity was improved by two-color laser irradiation.

A plane wave model has been developed to describe the dynamic behavior of end-pumped CW quasi-three-level lasers. We have derived algebraic equations and analytic expressions from a set of coupled rate equations. The analytic expression predicts that characteristics of a laser are affected not only by the Boltzmann occupation factor of the pump states, but also by that of the laser states. To illustrate the utility of the model, an end-pumped Yb:YAG laser oscillator was investigated and optimized. We have examined the threshold value of the pump beam, pump beam depletion in the gain medium, optimal crystal length, and laser output power for a given pump power. Finally, we have shown the pump and laser intensities and the population of each manifold as a function of crystal length.

A temperature measurement scheme was proposed in a diode end-pumped thin monolithic Yb:YAG laser by analyzing the red-shifting behaviors of each lasing peak. The amount of peak shift was measured on the basis of the threshold lasing spectrum by using a chopped pump beam. In order to determine the effective scale factor, the ratio between the peak shift and the temperature rise, the dynamics of the spectral shift, the output beam profile, and the output power were investigated. The effective scale factor was determined to be about 0.0114 nm/°C in the case of the crystal sandwiched by copper bocks with a hole, wherein the plane stress approximation is valid. On the other hand, the effective scale factor significantly decreased in the case of the crystal sandwiched by sapphire plates.

In order to study autoionizing states of zirconium, we performed three-photon polarization spectroscopy. Three dye lasers were used as atomic excitation sources. The first two dye lasers charged with rhodamine 570 were pumped by the second harmonics of a Nd:YAG laser. Atoms in the high-lying even parity levels were excited to autoionizing states and ionized by scanning the third dye laser, which was pumped by the third harmonics of the Nd:YAG laser.