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Magnetic Materials Drive Up Power of Compact Q-Switched Laser
Aug 2016
AICHI, Japan, Aug. 15, 2016 — A submillimeter-thick film with magnetic microdomains has been used to control a Q-switched laser, increasing its pulse power by 1,000 times. The laser, developed using a 190-µ-thick garnet film with labyrinth-shaped magnetic domains, may be the first magneto-optic (MO) Q-switched laser developed using thin magnetic garnets.

Magnetic Materials
Ph.D. candidate Ryohei Morimoto (left) and assistant professor Taichi Goto working with the MO Q-switched laser. Courtesy of Toyohashi University of Technology. All Rights Reserved.

Researchers at Toyohashi University of Technology, Iowa State University and the Institute for Molecular Science obtained an active Q-switched microchip laser (MCL) whose repetition rate, pulse width, mode-lock stability and pulse could be controlled. To do so, they exploited the MO effects in magnetic films that possess a garnet structure.

"The most difficult part of realizing MO Q-switching was to combine three different techniques/fields: the preparation of a magnetic material, the fabrication of a high-speed magnetic field switch and the construction of a laser cavity," said researcher Ryohei Morimoto.

Using a custom-made coil and circuits researchers generated a pulsed magnetic field which was applied to the magnetic garnet, to actively control the film and generate an optical output with a pulse width of tens of nanoseconds. The technique achieved precise pulse control in the Q-switched laser and enhanced its output power by a factor of 4 × 103.
Toyohashi University of Technology

A pulsed output with a power of dozens of watts and a pulse width of 40 ns was obtained through an MO Q-switched laser controlled by labyrinth-shaped magnetic domains. Courtesy of Toyohashi University of Technology. All Rights Reserved.

Researchers also discovered that when a ring-shaped permanent magnet was placed close to the magnetic garnet, they were able to generate the same optical pulse in the MO Q-switched laser using seven times less electric power. This result indicated that the Q-switch would not need a large power supply for operation.

"The device was two orders of magnitude smaller than other reported controllable Q-switches," said professor T. Taira.

The researchers’ approach was inspired by bulk-based electro-optic (EO) and acousto-optic (AO) Q-switches, which are widely used in cavity laser systems. However, these components are difficult to integrate into MCLs because of their size and mechanisms. In addition, they typically require a large-size power supply, which hinders the entire system from being downscaled.

The researchers have demonstrated what is believed to be the first evidence of a Q-switched laser driven by magnetic domain motions and the first evidence of the possibility of an integrated Q-switched laser.

"There are no previous reports of MO Q-switches using thin garnets. This is surely the first demonstration, and it also becomes an important first step in the development of an integrated high-power laser," said professor Taichi Goto.

The novel type of active Q-switch developed by the research team can be combined with a microlaser to obtain megawatt-order pulses and may extend the scope of compact high-power laser applications.

The research was published in Optics Express, a journal of the Optical Society of America (doi: 10.1364/OE.24.017635).

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