400-W Diode-Pumped Solid-State Green laser

Abstract

More than 400-W green laser power was generated by second-harmonic generation of a Q-switched diode-pumped Nd:YAG laser at a repetition rate of 8 kHz. This power is, to our knowledge, highest in solid-state green lasers.High power green lasers are expected in many applications, such as the laser annealing and the precise material processing. The laser annealing technique is commonly used in product lines in order to crystallize amorphous silicon films into polycrystalline silicon (poly-Si) films for the fabrication of thin film transistors (TFTs). The poly-Si TFTs are used for high-precision high-quality flat panel displays (FPD), such as liquid crystal displays (LCD) and organic light emitting diode (OLED) displays. So far, excimer lasers have been applied as the laser source for laser annealing1' 2). However, there are some problems in this method. One is the high maintenance cost, and the other is the limited process window of the optimum laser energy density for obtaining the maximum mobility3).The problem about the maintenance cost is caused by many maintenance items of excimer lasers, because excimer lasers are pumped by discharge in halogen gas, and the chemical vapor doping is occurred by UV beam. Short-term maintenance items are laser gases and cleaning windows, and long-term maintenance items are laser windows, gas refinement systems, a thyratron switch, and a laser chamber, and so on.To overcome these problems, diode-pumped solid-state green lasers were demanded alternatively, because the maintenance item is only frequency conversion crystal, and the process window obtained by a green laser is more than twice wider than that by an excimer laser3). To use diode-pumped solid-state green lasers as a light source for laser annealing in product lines, the high power and the high energy are necessary. Authors have already proposed a 200-W, 50-mJ diode-pumped solid-state green laser as a light source for laser annealing4). In order to high-speed laser annealing, we have tried to make green lasers higher power. In this paper, we report on the over 400-W green beam generation by second-harmonic generation of a Q-switched diode-pumped Nd:YAG laser. Figure 1 shows the schematic drawing of a Q-switched diode-pumped Nd:YAG green laser. The simple external-cavity frequency-conversion scheme is applied in consideration of the practical use and the easy maintenance. A Q-switched diode-pumped Nd:YAG laser is used as a light source for frequency conversion, which consists of an oscillator and amplifiers with rod-type laser materials. An efficient diode side-pumping configuration is applied for diode-pumping modules in this laser5' 6). This pumping configuration has long-term working records in high-power IR lasers for metal welding in product lines. The type-II phase-matching LBO (LiB305) crystal of 18-mm long is used for frequency conversion. The temperature of the crystal was controlled at nearly room temperature with the accuracy of 0.1 degree for the stable operation. The IR laser beam generated by the Q-switched di...

High efficiency 125 J second-harmonic generation from CsLiB_6O_10 nonlinear crystal by diode-pumped Nd:glass laser

“…Frequency conversion is useful technique for extending utility of high power lasers [1,2]. Second-harmonic generation (SHG) of near infrared lasers is essential technique to use for a pumping source of Ti:sapphire lasers and optical parametric amplifiers [3][4][5].…”