Yoshimatsu Laboratory
Nd:YAG Laser (#1)
LOTIS TII Nd:YAG laser LS-2145
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Fundamental (1064 nm), 2ω (532 nm), 4ω (266 nm) wavelength
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This laser can be used for laser ablation in PLD method since it can irradiate laser with long pulse width of 14-16 nm.
Controlling energy in Nd: YAG laser
The laser energy value is a very important parameter in the PLD method, which determines the plume state. There are three ways to control the energy value:
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Keep the laser conditions constant and adjust the energy with an attenuator.
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Adjust the output energy based on the laser conditions.
Our laboratory uses method 2. The above figure shows the relationship between the flash lamp pump energy, Q-switch delay, and laser power for 2ω (wavelength: 532 nm) and 4ω (wavelength: 266 nm). In the case of 4ω, the pump energy is fixed at 16.5 J, and the Q-switch delay is changed from 136 to 240 µs, modulating the laser energy in the range of 20 to 70 mJ.
Design and adjustment of the optics in PLD
Top: Optical system of our laboratory's PLD. Bottom left: Focusing lens
Bottom center: Beam expander
Bottom right: Relationship between lens position and laser area. Area was calculated using graph paper and Image J.
In the PLD method, an ultraviolet laser that ablates the target is introduced into the PLD chamber from outside through a view port. Our laboratory has set up an optical system as shown in the left figure. To reduce damage to the mirror, lens, and view port, a fixed magnification beam expander (x2) is placed directly below the Nd:YAG laser. A laser shutter is installed between the first and second mirrors. A φ9 mm aperture is installed in front of the focusing lens to clean the laser profile.
By introducing thermal paper onto a target holder and moving the focusing lens, the laser irradiation area can be visualized. The left figure shows the results when the focal position is set to 0 mm and the lens is moved 70 mm away. The area is systematically changed from 0.3 mm to 2.5 mm, and it can be seen that the area fits well as a quadratic function of the lens position.
The optical system is aligned using a He-Ne laser through a viewport on the back of the PLD chamber. This method allows for accurate reproduction of the relationship between lens position and laser area.
Typical laser conditions using this optical system are 0.5 J/cm2 (energy: 7.5 mJ, area: 0.15 cm2).