Wireless optical power transmission based on the off-axis VECSEL of long resonator

• Ultra-long cavity semiconductor laser with cavity length over 2 m for wireless power. • Adjustable beam supports large pumping spot to achieve high power output >700 mW. • The laser output operates deviating from the optical axis. • Laser power decreased by 5.5% when off-axis range increased by 40.7%. We present laser generation in a several-meters-long air cavity using an optically pumped semiconductor gain chip for wireless optical power transmission applications. Theoretical calculations showed that stable laser oscillation can be realized in long laser oscillation cavities of more than 500 cm. Moreover, the laser oscillation can be maintained even when the output mirror of the laser is off-axis, which is useful in the alignment of energy charging terminals. A lens was inserted into the cavity to adjust the intra-cavity beam, and the beam radius on the gain chip surface sufficiently increased to match a large pump spot and achieve high output power. Laser generation in an external air cavity of 200 cm was realized, and the maximum output laser power of more than 705.4 mW was achieved. The off-axis range of the output mirror surpassed 19 mm. Moreover, the output laser power decreased by 5.5 % (from 586.4 to 554.2 mW) when the length of the external air cavity was increased from 100 to 200 cm. However, the off-axis range increased by 40.7 % (13.5 to 19 mm). Thus, the longer external cavity laser made it easier to align the laser beam and charging terminal.