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This page describes an outdated design. The up-to-date version can be found here. |
Laser setup
The laser source of the LASER4DIY project is a diode pumped solid state laser with a Neodymium-doped yttrium orthovanadate (Nd:YVO4) crystal. This widely-used laser is especially suitable for this usecase, since the Nd:YVO4 cristal is cheap, easy to obtain and also, based on the use of the so called bounce geometry, very powerful. In figure 1 you can see the setup of the laser system, which is very similar to the puplication by Thomas and Damzen, 2011 [1]
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Because the pump light is only exciting a part of the Nd:YVO crystal and therefore a temparture gradient is formed, a thermal lense occurs. Dependend on how big the temperature gradient is, a different refractory index occurs, which let the emitted radation leave the crystal under a different angle. To tune the laser beam to maximum power than the lengths L1 and L2 (see figure 1) has to be adjusted to this angle.
Simulation of the laser source
Simulation was done using the program LASCAD. A finite element analysis (FEA) for the thermal effects of the Nd:YVO4 crystal is possible with it, allowing to determine the exact geometry of the resonator. Especially the distances of mirror 1 and the uncoupling mirror to the crystal (see figure 1) are important for the construction later on. Additionally the simulation program can calculate the average power in CW mode (continuous wave mode), as well as the peak power of the laser source when using the Q switch. The simulation was done without frequency doubler, as it is less important for the laser geometry.
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Figure 5: Temperature distribution for simulated crystal
Simulation Results
The following simulatino results were calculated with distances L1 = L2 = 25 mm between the reflection mirrors and the crystal. As only an approximation of the bounce geometry could be simulated, a deviation of up to 50% with the resulting output pwoer figures must be considered.
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The results of the performed simulations show much higher output power figures than to be expected regarding the experiments done by Thomas und Damzen, 2011. Nevertheless the results can serve as a starting point for the setup of the mirrors when building the resonator. Additionally, the simulation showed, that the used setup of the laser with a Nd:YVO4 crystal can provide enough power for the ablation of copper.
Conclusion
The results from the simulation performed generally showed significantly higher output powers than could be expected under real conditions according to [1]. In an experiment, we have shown that this setup works in principle and is also suitable for generating laser pulses with peak powers that are sufficiently high for the ablation of copper, even if the values from the simulation – as expected – could not be achieved.
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For these reasons, we looked for an alternative setup that on the one hand increases the possible peak performance and on the other hand makes it easier to adjust the system. The resulting setup is described here.
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Literature:
[1] G. M. Thomas and M. J. Damzen, “Passively Q-switched Nd: YVO 4 laser with greater than 11W average power,” Opt. Express, vol. 19, no. 5, pp. 4577–4582, 2011.
[2] “Betrieb von Lasereinrichtungen,” Berufsgenossenschaft der Feinmechanik und Elektrotechnik, Berufsgenossenschaftliche Informationen für Sicherheit und Gesundheit bei der Arbe 832, 2003.
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