Jui-Yun Yi

Multi-reentrant nonplanar ring laser cavity

A multi-reentrant nonplanar ring laser cavity configuration is presented. Two identical spherical mirrors were used to construct the laser cavity. The exact reentrant condition of the ring cavity is derived and the stability of the laser cavity is analyzed. Although slight astigmatism can arise from the intracavity elements, the cavity itself is astigmatism-free. Linear output polarization is readily achieved. A 3-atm.% Nd doped YAG with 1-mm thickness was used as the gain medium to reduce beam distortion, and the gain medium also served as a Faraday rotator to control the laser beam propagation direction. The laser cavity length is short, whereas the laser beam round-trip length can be long. A factor of 13-times enlargement in round-trip length is demonstrated.

Efficient and compact Yb:YAG ring laser

An efficient and compact Yb:YAG ring laser was demonstrated with a slope efficiency of 39.0% with respect to the absorbed power. The design issues for using Yb:YAG as the gain medium in the reentrant multipass ring laser are discussed. The high absorption coefficient and low quantum defect of Yb:YAG make it an ideal gain medium for the multipass ring cavity to fulfil reentrant condition and reduce reabsorption loss. The absorption characteristics of a 20-at.% doped Yb:YAG crystal and the optimum ratio of absorption depth to Yb:YAG thickness were measured. The degrees of linear polarization were 99.0% and 94.1% in planar N=2 and nonplanar (N,M)=(2,1) ring lasers, respectively. The multipass ring cavities can be applied in a compact mode-locked laser with long round-trip length

Study of Short-Wavelength Yb:Fiber Laser

Yb:fiber lasers have shown excellent performance in 980- to 1100-nm wavelength range. Below 980 nm, the small ratio between emission and absorption cross sections hindered its development. To find out a feasible solution for short-wavelength Yb:fiber laser, the temperature-dependent emission and absorption cross sections, fiber length, pumping method, and suppression of high-gain wavelengths are analyzed and discussed. It is interesting to find that elevated temperature of the gain fiber is beneficial for short-wavelength Yb:fiber laser generation, which is opposite to general perception of quasi-three-level lasers. In this paper, a 960-nm Yb:fiber laser with 20.1% slope efficiency is successfully developed at 101°C, which is the shortest wavelength of Yb:fiber laser to our knowledge. And this 960-nm Yb:fiber laser can be applied in generating blue light for large-screen laser display.

Planar Multipass Ring Laser Cavity

A planar multipass ring laser is demonstrated using a pair of spherical mirrors. The reentrant conditions of ring cavities are derived. The stabilities of laser cavities are also analyzed. A 3 atm.% Nd-doped YAG crystal of 1 mm thickness was used as the gain medium. The laser output is polarized even for cubic gain media. The polarization ellipticity is increased by a factor of 23.8 in a planar ring cavity compared with that in a nonplanar ring cavity.

Compact Passively Q-Switched Yb:YAG Multipass Ring Lasers

An efficient and compact continuous-wave Yb:YAG laser with a slope efficiency of 50.3% with respect to the absorbed power was demonstrated using a multipass ring cavity (MPRC). Large cavity length ranges can be implemented using MPRCs with the same optical elements but different beam configurations. When Cr:YAG was used as the saturable absorber for passive Q-switching, various pulse widths and repetition rates were obtained. When a two-mirror MPRC, which is a compact ring laser cavity was used, the spatial hole-burning effect was reduced, and the spontaneous noise from the gain medium was not directly incident on the saturable absorber, causing less perturbation of the population difference of the saturable absorber than that of a linear cavity. This indicates that MPRCs can reduce the time jitter problem of a passively Q-switched laser. In this study, a Yb:YAG MPRC laser with a 33 ns pulse width is demonstrated, and the timing jitter of the repetition period was restrained to around 11%. The obtained experimental results are in good agreement with simulation results.

Short-wavelength Yb:Fiber laser

The small ratio between emission and absorption cross sections below 980 nm hinders Yb:fiber lasers development. The temperature, fiber length, and suppression of high-gain wavelengths are analyzed and a 960-nm laser is successfully developed.

Ytterbium-Doped Yettrium Aluminum Garnet Crystal Fiber Multipass Ring Laser

We report the growth of ytterbium-doped yettrium aluminum garnet (Yb:YAG) crystal fibers by the laser-heated pedestal growth (LHPG) method. The characteristics of Yb:YAG crystal fibers were analyzed by electron probe microanalyzer (EPMA) and X-ray diffraction measurements. The small crystal fiber diameter makes it effective for heat removal from a high-Yb3+-concentration and quasi-three-level gain medium. The length of this crystal-fiber-based high absorption can be shorter, which is eminently suitable for a multipass ring cavity to maintain cavity stability and mode symmetry. We successfully demonstrated a two-mirror multipass ring laser with 54.7% slope efficiency, which is higher than the 50.3% for a bulk Yb:YAG laser.

Compact Multi-pass Ring Laser Using LHPG-grown Yb:YAG Crystal Fiber

Yb:YAG crystal fiber was fabricated by laser-heated pedestal growth method for the first time. It was applied in a multi-pass ring laser with 54.7% slope efficiency, which is higher than 50.3% of using bulk YbYAG.

Planar and non-planar multi-reentrant 2-mirror ring cavities

Summary form only given. Planar and non-planar multi-reentrant ring cavities are demonstrated. We have successfully derived the reentrant condition and obtained good agreement with the experimental results. The stability criteria have also been analyzed. Long round-trip length can be achieved with short cavity length by using the multi-reentrant ring laser cavities. They have the advantage for a mode-locked laser to have a ten-fold reduction in cavity length compared to a conventional linear cavity. They can also be used in trace gas detection for increasing the sensitivity compared to the multi-pass cell technique.