Characterization of high power laser diode as a solid state pumping source

Abstract

Laser diode is popular to be used as an optical pumping source, taking an advantage because it is small in size and light in weight. On the other hand, the laser diode creates a lot of heat dissipation because it was injected by a current. Due to the cuteness of active medium, it will generate a large beam divergence. In attempt to demonstrate the issue and overcome these problems, two laser diodes were characterized and an investigation is carried out to stabilize the output. The first laser diode bar was purposely employed to highlight the issue of beam divergence. The second laser diode is highly collimated and capable to be focused. However, both lasers are not stable, meaning no cooling is provided. Two collimators model FLA40B and FLA15 were used to reduce the beam divergence of laser diodes. The stability of laser diode is identified by operating the laser in free running mode. Knowing that the output turn out to be very small, the result indicates that the laser required stabilizer. Fan extractor and heat sink were introduced in the system. Realizing that the output is still not stable, a Thermoelectric Cooler (TEC) was designed and constructed. After stabilizing the lasers system, they were utilized to pump orthovanadate Nd:YVO4 crystal disk. The fluorescence beams were detected via spectrum analyzer. The pumping by using collimated high power laser diode was further enhanced by focusing the beam into an active medium and filtering the emission radiation using IR filter. The result obtained shows that, the laser diode produce output power of 1.8 W without cooling system with differential responsivity of 0.21 W/A and an efficiency of 8%. With TEC provided the laser power increased up to 4.6 W with power conversion of 12%. The output power of collimated beam achieved up to 8.6 W with differential responsivity of 0.54 W/A and an efficiency of 27%. Both laser diodes produced fundamental wavelength center at 808 nm. This is a suitable absorption band for orthovanadate crystal. However, the spectrum gain of the laser diodes is kept on broadening at higher pumping current. Changes in refractive index and the increase in active zone were the cause to the spectrum gain’s broadening. The emission spectrum comprised of 878 nm, 917 nm with majority line of 1064 nm. It is also noticed that by focusing the high power laser diode and filtering the output, the emission radiation becomes more pronounce and significant.