An international team of scientists has produced the first high-powered, randomly polarised laser beam with a “Q switch” laser, which typically emits pulses of light so brief that they’re measured in nanoseconds.
Goto and his team used Q switching, along with a laser a tenth of the size of an American penny, to produce a laser beam ten times more powerful than previously reported with a larger laser.
Above – Diode-pumped magnetooptical (MO) Q-switched laser. (a) Schematic of laser cavity setup. The rare-earth substituted iron garnet (RIG) film was sandwiched by a pair of coils and its magnetisation was modulated by a pulsed field. The minimum cavity length L was 10 mm. (b) Beam diameter (thick orange line) estimated using ABCD matrix method and refractive indexes (thin blue line) in cavity.
Along with the change of laser size, the researchers also adjusted the magnetic material through which the light travels and amplifies to a more powerful pulse. With the addition of a neodymium-yttrium-aluminum-garnet, Goto could use magneto-optics to better control how the light moves within the laser cavity.
The short pulses allow the researchers to change the polarization of the laser through manipulation of the photons comprising the light. Instead of a constant light, each pulse can be switched. The laser size means the energy punches out, instead of dissipating as it travels inside the system.
The researchers plan to increase the peak power of their system, according to Goto. They also plan to apply the system as an integrated microlaser for further testing.
Diode-pumped solid-state micro lasers are compact (centimetre-scale), highly stable, and efficient. Previously, we reported Q-switched lasers incorporating rare-earth substituted iron garnet (RIG) film. Here, the first demonstration of the magnetooptical (MO) Q-switch in an Nd:YAG laser cavity is performed. We fabricate a quasi-continuous-wave (QCW) diode-pumped Nd:YAG laser cavity, which is shortened to 10 mm in length and which contains an RIG film and a pair of small coils. This cavity yields a 1,064.58-nm-wavelength pulse with 25-ns duration and 1.1-kW peak power at a 1-kHz repetition ratio. Further, the polarisation state is random, due to the isotropic crystal structure of Nd:YAG and the fact that the MO Q-switch incorporating the RIG film does not require the presence of polarisers in the cavity. This is also the first report of an MO Q-switch producing random polarisation.
This study demonstrates integrable MO Q-switching using RIG film in an Nd:YAG laser system for the first time. The 10-mm-long cavity produced 1.1-kW peak power and a 27-ns-long output at a centre wavelength of 1064.58 nm via QCW diode pumping, generating randomly polarised pulses. The repetition ratio was 1 kHz. In addition, the output polarisation state was confirmed to be random and an M2 value of 3.7 was obtained. In this laser system, the Q-switch and the lasing material have a similar crystal structure; therefore, the MO Q-switch and the Nd:YAG can be combined into actively Q-switched micro lasers, similar to epitaxial growth31 or bonding of passive Q-switches on lasing materials (e.g., Cr4+:YAG on Nd:YAG)32,33. The experimental evidence provided in this study advances this research field toward the realisation of actively controllable integrated micro lasers.
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