Pi-Ling Huang

Passively Q-switched quasi-three-level laser and its intracavity frequency doubling

A passively Q-switched quasi-three-level Nd:YAG laser is intracavity frequency doubled to generate a blue laser. The 473-nm blue laser has a peak power of 37 W and a pulse width of 23 ns at a pumping power of 1.6 W. To model this laser numerically, we developed rate equations by taking into consideration both the quasi-three-level nature of the gain medium and the four-level nature of the saturable absorber. Good agreement was achieved between experimental and simulated results for both the fundamental and the second-harmonic output. The reabsorption loss of the gain medium is estimated under pulsed operation.

Non-invasive characterization of the domain boundary and structure properties of periodically poled ferroelectrics

Shaping the ferroelectric domains as waveguide, grating, lens, and prism are key to the successful penetration of periodically-poled ferroelectrics on various wavelength conversion applications. The complicated structures are, however, difficult to be fully characterized, especially the unexpected index contrast at the anti-parallel domain boundaries are typical in the order of 10(-4) or less. An ultrahigh resolution optical coherence tomography was employed to fully characterize the domain boundary and structure properties of a periodically-poled lithium niobate (PPLN) waveguide with an axial resolution of 0.68 μm, an transversal resolution of 3.2 μm, and an index contrast sensitivity of 4x10(-7). The anti-parallel domain uniformity can clearly be seen non-invasively. Dispersion of the ferroelectric material was also obtained from 500 to 750 nm.

Efficient Nd:Y3Al5O12 Crystal Fiber Laser

Efficient Nd:Y3Al5O12 (Nd:YAG) lasers were demonstrated using gradient-index crystal fibers. A laser output power of 145 mW was achieved along with a slope efficiency of 28.9%. Up to 40% higher Nd ion concentration compared to that in the source rod at the center of the crystal fiber was obtained. Measurement by low-coherence reflectometry indicated an index difference of 0.0284 between the center and the edge of the crystal fiber.

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.

Reentrant two-mirror ring resonator for generation of a single-frequency green laser

A nonplanar, reentrant two-spherical-mirror ring cavity is demonstrated. It is compact and free of astigmatism. Unidirectional operation is achieved by use of reciprocal and nonreciprocal polarization rotators to differentiate round-trip loss. A single-frequency green laser is generated by intracavity frequency doubling. Amplitude noise as low as 0.25% is achieved.

Fabrication and Characteristics of Ce-Doped Fiber for High-Resolution OCT Source

The fabrication of Ce-doped fibers (CeDFs) is demonstrated by drawing-tower method employing rod-in-tube technique. The fluorescence spectrum of CeDFs with a 16-μm core exhibited a 160-nm broadband emission with 1.45-μm axial resolution. This CeDF may be functioned as a high-resolution light source for optical coherence tomography applications.

A Passively Q-Switched Laser Constructed by a Two-Mirror Reentrant Ring Cavity

A passively Q-switched laser is demonstrated by a two-mirror reentrant and unidirectional ring cavity. Due to the cavity configuration, the pulse-to-pulse timing jitter is effectively reduced to less than 3% over 40,000 shots. As indicated in our simulation on photon dynamics in the cavity, spontaneous noise from the gain medium is the major cause of large timing jitter in passively Q-switched lasers, and it is eliminated in this laser.

Measurement of temperature gradient in diode-laser-pumped high-power solid-state laser by low-coherence reflectometry

A noninvasive technique was developed to measure the temperature distribution in laser gain medium. Both axial and radial temperature distributions of a diode-laser-pumped and intracavity frequency-doubled high-power Nd:YVO4/KTP laser were characterized using a high dynamic range, low-coherence reflectometer. This measurement is important to the design of high-power solid-state lasers both in terms of mode matching and laser-rod doping selection.

Gain Enhancement of Single-Mode Cr-Doped Core Fibers by Online Growth System

Gain enhancement of single-mode Cr-doped crystalline core fiber (SMCDCCF) with longer fiber length fabricated by online laser-heated pedestal growth (LHPG) technique is demonstrated. In comparison with the SMCDCCF fabricated without online growth, the online technique enables real-time monitoring and controlling small molten zone in the LHPG to achieve longer length with better uniformity and smaller core diameter of the SMCDCCFs. The SMCDCCF exhibits a length of 10.6 cm, a core diameter of 25 μm, and a V-value of 2.40, which confirms the LP01 single-mode operation by the far-field pattern measurement. A 3.9-dB gross gain and a 1.9-dB net gain of the SMCDCCF at the wavelength of 1400 nm were obtained. The gross and net gains are the highest yet reported of the SMCDCCFs. Further development on higher gain of the SMCDCCF may be functioned the SMCDCCF as a broadband fiber amplifier for use in the next-generation fiber transmission systems.

Polarization Analysis of a Nonplanar Reentrant Ring Laser Cavity

The study of polarization evolution in a nonplanar, reentrant ring cavity is reported. In the numerical simulation, the factors which affect the polarization state within the cavity were considered. By measuring the polarization of a linear-cavity laser, we also derived the thermally induced optical axis rotation in the gain medium, and determined the equivalent themperature-dependent dielectric tensor of the gain medium at various pump powers, which enable Jones matrix analysis of the polarization in the nonplanar ring laser cavity. The laser cavity is compact and suitable for applications in cases in which unidirectional propagation is required. A highly stable single-frequency green laser was generated with an amplitude noise of less than 0.35%.