Norio Karube

Laser-induced cleavage of LCD glass as full-body cutting

The laser-induced cleavage of LCD glass is free from the generation of cullet and micro-crack, dispensing with the subsequent processes of grinding and cleansing. This paper deals with the theory and experiment of this technology which can improve the manufacturing of flat panel displays. Different from the preceding technology using CO2 laser irradiation which can realize surface absorption and scribing only, we have realized the surface/inward absorption of laser beam inside glass by matching the absorption characteristics of glass and the emission wavelengths of appropriate lasers and have succeeded in realizing the full-body cleavage of LCD glass. We have also succeeded to develop the technologies, which can eliminate the shortcomings so far considered to be inherent to this full-body cleavage, i.e. size effect. The completion of the full-body cleavage in this way can simplify the manufacturing process of LCD.

1.1-kW high-efficiency LD-pumped Nd:YAG laser

Recently, the development of multi-kW all solid-state lasers for industrial applications has been evaluated for the energy saving characteristics. We report the laser oscillator using the LD pumped slab Nd:YAG producing the highest efficiency on the cooling condition of room temperature. The two-side pumping is generally used for realizing symmetrically distributed excitation and temperature in the crystal. However, there exist two demerits coming from the useless LD pump light which is not absorbed in the slab. The first demerit is the fact that this light does not contribute to laser oscillation and the second one that the same light degrades the performances of LDs locating on the opposite side. We have eliminated these demerits by employing the one- side pumping method in which LDs are located on one side of the slab and a highly reflecting mirror is located on the other side. Based on this concept, the LD pumped slab Nd:YAG laser has been developed using a 6 X 25 X 206 mm3 slab crystal. The average output power of 1109 W and the peak output power of 4900 W have been obtained with the optical efficiency of 40.6% and the electrical efficiency of 15.3% on the cooling condition of 299 K.

Thermal analysis of high-power LD-pumped slab Nd:YAG laser

We have developed a high power LD pumped Nd:YAG laser using one zig-zag slab crystal, and obtained the average output power of 3.3 kW with the optical efficiency of more than 35% under the cooling condition of 12 degrees Celsius. Our method is to mount the LD stacks on both the sides of the 6 mm X 25 mm X 206 mm slab crystal in which the LD stacks mounted on one side of the slab pump the upper part of it while the ones on the other side pump the lower part. The LD pump light transmitted through the crystal is reflected by Au mirror and is introduced back into the slab. These LD stacks are arranged so that the thermally induced birefringence can be eliminated by maintaining uniform pumping in the width direction of the slab (non-zig-zag direction). The pumping distribution in the width direction was made constant by ray tracing simulation. The small signal gain distribution was measured constant in this direction, which indicates that the pumping distribution in the width direction has become uniform. The total heat generated in the slab was calculated to be less than 2.3 kW and the temperature distribution and thermal stress distribution were also simulated. According to this calculation, the maximum thermal stress of 40 MPa occurs in the surface of the slab, which is one-fourth of the fracture limit of YAG crystal.

Analysis of CO2 laser beam suitable for thick metal cutting

In dealing with CO2 laser beams, it is often observed that the beam does not obey optical formula that are valid in lower power situations. This is particularly true with the beams of low order mode and power greater than 2 kW. Traditional approaches aimed at improving focussing characteristics of such beams may actually produce the opposite effect. An analysis was made concerning optical distortion caused by laser beam heating of transmission optics. The distortion in the output coupling mirror was observed to give rise to a spike that may be observed in the near-field. The distortion that takes place in the focussing lens has been found to cause serious deterioration of its focussing property. A beam mode that offers good focusing while avoiding the occurence of distortion was pursued theoretically. Good agreement between the theoretical and experimental observations of focussing properties was achieved. Additionally the resultant cutting performance correlates well to the measured focussing characteristics. As a result of this analysis it can be demonstrated that a 2 kW CO2 beam can cut up to 20 mm thick mild steel with good surface quality.In dealing with CO2 laser beams, it is often observed that the beam does not obey optical formula that are valid in lower power situations. This is particularly true with the beams of low order mode and power greater than 2 kW. Traditional approaches aimed at improving focussing characteristics of such beams may actually produce the opposite effect. An analysis was made concerning optical distortion caused by laser beam heating of transmission optics. The distortion in the output coupling mirror was observed to give rise to a spike that may be observed in the near-field. The distortion that takes place in the focussing lens has been found to cause serious deterioration of its focussing property. A beam mode that offers good focusing while avoiding the occurence of distortion was pursued theoretically. Good agreement between the theoretical and experimental observations of focussing properties was achieved. Additionally the resultant cutting performance correlates well to the measured focussing characteris...

1.7kW high efficiency LD pumped Nd:YAG laser

Material processing kilowatt-class LD pumped solid-state lasers have been actively developed to be used in such industries as automotive, aerospace, electronic and so on. In this development, the key technologies are the following two, i.e. development of high power LD possessing high efficiency and thermal management within the laser crystal.

Laser‐induced full body cleavage of flat‐panel‐display glass

— Of the two types of thermal-stress processes for glass, i.e., surface scribing and full body cleavage, the latter is not presently applied in commercial manufacturing due to the technical difficulties, notwithstanding its various advantages. These difficulties, which were pointed out by Kondratenko and were refered to as size effect, consist of a reduced processing speed in a large glass plate and the positional inaccuracy when cleaving close to edges of a glass plate. The result of the investigation aimed to solve these problems, which can pave the way to the commercial application of full body cleavage in the manufacturing of flat-panel-display (FPD) devices, is reported.

49.1: Invited Paper: Laser-Induced Full Body Cleavage of Glass for FPDs

In this paper, we describe the laser-induced full body cleavage of FPD glass, i.e. its technology and properties of work processed by it. It is the next generation technology after the surface scribing using CO2 laser irradiation. The removal of size effect which was considered to be inherent to full body cleavage was the main subject of this investigation.

LD-pumped slab Yb:YAG laser

In recent years, the high power Yb:YAG lasers have been actively investigated due to the advantage of the high quantum efficiency of 91% which reduces the thermal loading in the Yb:YAG crystal. So far, the Yb:YAG laser with the output power higher than several hundreds watts has been developed using the crystal configurations of rod and thin disk. We have developed the Yb:YAG laser by employing the rectangular slab crystal in order to examine the possibility of realizing the high power slab Yb:YAG laser. The dimension of the Yb:YAG crystal used is 1 mm X 5 mm X 10 mm and its configuration is a rectangular parallelepiped, and the density of Yb is 1.1 atom%. The LD (Laser Diode) pump light focused with plano-convex lens is introduced through the 1 mm X 10 mm plane of this slab which is AR-coated at 940 nm while the opposite 1 mm X 10 mm plane is HR-coated at the same wavelength. The Yb:YAG laser cavity axis is in the direction perpendicular to the 1 mm X 5 mm planes which are AR-coated at 1030 nm. The two 5 mm X 10 mm planes are cooled by being contacted with the copper heat sinks which are cooled by the water at the temperature of 18 degrees Celsius. The CW output of 35 W was obtained when the power of LD pump light was 496 W. The optical efficiency was 7.1% with the optical slop efficiency of 12.2%.

2.5-kW slab Nd:YAG laser using a 400-mm-long crystal bonded by optical contact method

The optical contact method has been developed to obtain a large volume slab Nd:YAG crystal for achieving a multi-kW output power. The bonded crystal with the dimension of 6 X 25 X 402 mm3 (tip to tip) is mounted in a single laser head and is pumped with four krypton arc lamps. In continuous wave (CW) operation, the maximum output power of 2480 W, the overall efficiency (eta) E-O of 4.0% and the slope efficiency of 5.5% have been obtained. A beam quality which is defined as the product of full divergence angle and diameter of the beam waist is better than 10 mm (DOT) mrad and 80 mm (DOT) mrad in the directions of the thickness and the width of the slab, respectively. The output laser beam was transmitted through a GI type 600 micrometer-core optical fiber completely. This configuration has realized a simple resonator laser producing high processing performance.

Industrial lasers in Japan

I am to report on some aspects of industrial lasers in Japan. Mostly centering on the market. In Japan, the history of laser developnent is rather profound. And long. Ever since the first invention of the laser in this country in 1960. This is partly because of the fact that in Japan the spectroscopic studies of the ruby was very popular in the late 1950s. Ever since niost of the work has been done in the research laboratories of the industry, not in the universities or not in the governmental laboratories. And since that time our first activity was mainly centering on the basic research, but after that time we have the evolution of the technology. One of the features in Japan is that the activity of developement and research of laser technology from the very basic phase up to the present commercialization has been done by the same group of people, including ine. We had a national project which ended about six years ago which was sponsored by MITI. MITI is Ministry of International Trade and Industry in Japan. And because of this national project, the effect of this project had a very enlightening effect in Japan. And after that our Japanese laser market became very flourishing.