Jaemin Han

X-ray astronomy in the laboratory with a miniature compact object produced by laser-driven implosion

It has been suggested that the extreme states of matter generated by high-intensity lasers could allow conditions similar to those in the vicinity of black holes to be studied in the lab. The observation of striking similarities between the X-ray spectra emitted by a laser-driven laboratory plasma and those measured from two high-mass binary star systems suggests such potential has been realized.

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.

Efficient diffusive reflector-type diode side-pumped Nd:YAG rod laser with an optical slope efficiency of 55%

We fabricated a compact diode side-pumped Nd:YAG laser with a diffusive reflector, in which the diode laser power is transferred directly into the threefold symmetric diffusive cavity through long narrow slits. With a 7.5% output coupler in a linear resonator, we obtained 62.4-W multimode output power with an optical slope efficiency of 53.4% at a diode power of 182 W, which corresponds to an optical-to-optical efficiency of 34.3%. The optical slope efficiency increased to 55.5% when we used an 11% output coupler. From the leakage power analysis method, the pumping efficiency was measured to be approximately 82%. We discuss the thermal lens and the slope efficiency with respect to absorbed power that is derived from the measured pumping efficiency.

Laboratory spectroscopy of silicon plasmas photoionized by mimic astrophysical compact objects

Photoionized plasmas are encountered in astrophysics wherever low-temperature gas/plasma is bathed in a strong radiation field. X-ray line emissions in the several kiloelectronvolts spectral range were observed from accreting clouds of binary systems, such as CYGNUS X-3 and VELA X-1, in which high-intensity x-ray continua from compact objects (neutron stars, black holes or white dwarfs) irradiate the cold and rarefied clouds. X-ray continuum- induced line emission accurately describes the accreting clouds, but experimental verification of this photoionized plasma model is scarce. Here we report the generation of photoionized plasmas in the laboratory under well-characterized conditions using a high-power laser. A blackbody radiator at a temperature of 500 eV, corresponding to a compact object, was created by means of a laser-driven implosion. The emerging x-rays irradiate a low-density (n(e) < 10(20) cm(-3)) and low- temperature (T(e) < 30 eV) silicon plasma. Line emissions from lithium- and helium-like silicon ions were observed from a thermally cold silicon plasma in the 1.8-1.9 keV spectral region, far from equilibrium conditions. This result reveals the laboratory generation of a photoionizing plasma. Atomic kinetic calculations imply the importance of direct K-shell photoionization by incoming hard x-rays.

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.

Stable Isotope Production of 168Yb and 176Yb for Industrial and Medical Applications

We have developed a laser isotope separation technology for the production of the 168Yb and 176Yb isotopes. 168Yb is very useful for the generation of a non destructive testing source, 169Yb. 176Yb can be used to produce 177Lu which is known to be a promising radioisotope for a medical application. For these applications, the abundances of 168Yb and 176Yb isotopes should be enriched to more than 15% and 97%, respectively. Our developed system consists of three dye lasers pumped by a diode-pumped solid-state laser, a Yb evaporator, and a photo-ion extractor. Up to now, we could enrich 168Yb to more than 31% with a productivity of 0.5 mg/h. Also, we succeeded in enriching 176Yb to more than 97% with a productivity of 27 mg/h.

270-W 15-kHz MOPA System Based on Side-pumped Rod-type Nd:YAG Gain Modules

We have developed a 270-W 15-kHz MOPA system based on side-pumped rod-type Nd:YAG gain modules. The master oscillator is a 3-W 15-kHz

Purification and laser isotope separation of 176 Yb for Medical Applications

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Frequency stabilization of the frequency doubled DOFA to the 127I2 line for calcium spectroscopy

Nd:YVO_4