Gwon Lim

Self-seeding in a dual-cavity-type pulsed Ti:sapphire laser oscillator

We have constructed a self-seeded Ti:sapphire laser oscillator by using a dual-cavity configuration that consists of a Littman configuration cavity and a partially reflecting feedback mirror. This configuration can be decomposed with two kinds of cavity, a grazing-incidence cavity and a standing-wave cavity. The former behaves as an injection seeder and the latter as a slave oscillator. This Ti:sapphire laser system is capable of delivering a continuously tunable laser pulse with a narrow linewidth. Injection at the laser emission region of the free-running Ti:sapphire laser resulted in essentially complete energy extraction.

External-cavity frequency doubling of a 5-W 756-nm injection-locked Ti:sapphire laser

We have developed a 5-W 756-nm injection-locked Ti:sapphire laser and frequency-doubled it in an external enhancement cavity for the generation of watt-level 378-nm single-frequency radiation, which is essential for isotope-selective optical pumping of thallium atoms. With a lithium triborate (LBO) crystal in the enhancement cavity, 1.1 W at 378 nm was coupled out from the cavity. Such results are to our knowledge the highest powers of continuous-wave single-frequency radiation generated from a Ti:sapphire laser and its frequency doubling.

Development of a 756 nm, 3 W injection-locked cw Ti:sapphire laser.

We have developed a 756 nm, 3 W single-frequency cw Ti:sapphire laser by using the technique of injection locking. A cw Ti:sapphire laser in a ring-type configuration was forced to lase unidirectionally by use of an optical diode to prevent a high-power backward laser from disturbing the injection laser. A master laser was amplified by a broad-area laser diode and coupled into a single-mode fiber to generate a 50 mW injection laser with a Gaussian beam profile, which was enough to lock the Ti:sapphire laser at full power of 3 W. Such a high-power single-frequency Ti:sapphire laser enables a watt-level blue or near-ultraviolet single-frequency laser to be generated by frequency doubling.

Investigation of Isotope Selective Characteristics of the Strontium Magneto-optical Trap by the Fluorescence Detection

The strontium magneto optical trap followed by a Zeeman slower has been demonstrated. The isotope selective characteristics of the trap have been investigated. The fluorescence spectrum of the MOT was compared with those of other high resolution spectroscopic methods. The red detuned deflection beam is also considered for a more selective spectrum.

Threshold reduction of stimulated Brillouin scattering by the enhanced Stokes noise initiation

A method of threshold reduction for stimulated Brillouin scattering (SBS) has been demonstrated in a SBS medium combined with a laser dye. It is based on the enhanced Stokes noise initiated by additional field with a Brillouin-shifted frequency component emitted from the laser dye in the SBS medium. Rhodamine 6G dye dissolved in SBS medium (ethanol), which was pumped by a 570 nm wavelength laser, was used to prove the SBS threshold reduction by the additional Stokes fields. The SBS threshold of this solution was reduced to a level about four times lower than that of the pure SBS medium. Also, the experimental results were investigated using the modified formula for the SBS threshold.

Transverse mode instability induced by stimulated Brillouin scattering in a pulsed single-frequency large-core fiber amplifier

We report the observation of transverse mode instability (TMI) in a pulsed single-frequency ytterbium-doped large-core fiber amplifier in which stimulated Brillouin scattering (SBS) is generated easily owing to the high peak power and narrow linewidth of the laser pulses. It was shown experimentally that the threshold of TMI is almost the same as that of SBS and that the suppression of SBS also increases the threshold of TMI, which indicates that the TMI originates from SBS in the fiber.

The influence of laser gain on stimulated Brillouin scattering in an active medium

The threshold and reflectivity of the stimulated Brillouin scattering (SBS) were investigated in an excited laser gain medium. The SBS in a steady-state was modeled numerically and its results for the threshold and reflectivity were compared with experimental results of SBS in a Rhodamine 6G solution pumped by a frequency-doubled Nd:YAG laser. It is demonstrated that the reflectivity has the maximum value at a certain intensity of an incident laser beam.

Development and Characterization of a 400-W Slab-type Nd:YAG Gain Module

We have developed a slab-type Nd:YAG gain module based on the techniques of conduction cooling and end pumping. The Nd:YAG slab is end-capped on both ends by undoped pure YAG and is pumped through the end-caps by stacked arrays of laser diode bars. The slabs surfaces of total internal reflection are in contact on both sides with microchannel cooling blocks which are cooled by water circulation. The power oscillator based on the gain module generates more than 400 W at 1-kW pumping with a slope efficiency of 55%. The small-signal gain of the gain module is 10 in a single zig-zag pass, and the amplified beam shows a near diffraction-limited beam quality.

DUAL-WAVELENGTH OPERATION OF A SELF-SEEDED DYE LASER OSCILLATOR

We demonstrate simultaneous dual-wavelength operation of a self-seeded dye laser. The laser cavity consists of one dye cell, two pairs of grating and tuning mirrors, and two reflecting mirrors. This configuration can be decomposed with two grazing-incidence cavities and a standing-wave cavity. The self-seeded dual-wavelength output beams are collinear and independently tunable. We were able to vary the output powers at the two wavelengths smoothly by changing the cavity length of a master oscillator.

Generation of continuous-wave single-frequency 1.5 W 378 nm radiation by frequency doubling of a Ti:sapphire laser

We have generated continuous-wave single-frequency 1.5 W 378 nm radiation by frequency doubling a high-power Ti:sapphire laser in an external enhancement cavity. An LBO crystal that is Brewster-cut and antireflection coated on both ends is used for a long-term stable frequency doubling. By optimizing the input couplers reflectivity, we could generate 1.5 W 378 nm radiation from a 5 W 756 nm Ti:sapphire laser. According to our knowledge, this is the highest CW frequency-doubled power of a Ti:sapphire laser.