Consequently, the device needs to be of length 20 mm or more, and a larger magnetic field is necessary for isolator applications. Even the commercially widely used TGG (Tb 3Ga 5O 12) material with a Garnet structure has a low Verdet constant at only around 36–40 rad Compared with those of the Fe-included magnetic type, paramagnetic type isolators have extremely small Verdet constants. The latter-paramagnetic material-has been applied for wavelength regions lower than 1.2 µm where iron garnet cannot be used. The former is represented by Bi-doped iron garnet and is commonly used in isolator applications owing to its high isolation performance. Polycrystalline ceramics are anticipated to be widely applied to the field of photonics in addition to laser applications.įaraday elements (Faraday rotator materials) that apply Faraday’s effect are classified into either Fe-containing magnetic material or paramagnetic material. However, recent studies have revealed that certain types of ceramic materials can provide novel characteristics that cannot be achieved in single crystals. Generally, ceramic materials are easily influenced by Mie scattering and Rayleigh scattering as they contain many grain boundaries which degrade the oscillation efficiency and laser beam quality when they are used as a laser gain medium. Since then, research and development on various types of ceramic laser materials and laser oscillation has been successively reported. In 1995, highly efficient laser oscillation using a polycrystalline Nd:YAG (Y 3Al 5O 12) ceramic material was reported for the first time. The laser damage threshold of this ceramic was 18 J/cm 2, which is 1.8 times larger than that of TGG, and it was not damaged during a power handling test using a pulsed laser (pulse width 50 ps, power density 78 MW/cm 2) irradiated at 2 MHz for 7000 h. ![]() The thermal lens effect (1/f) was as small as 0.40 m −1 as measured by a 50 W fiber laser. The insertion loss of this ceramic was equivalent to that of the commercial TGG single crystal (0.04 dB), and its extinction ratio reached more than 42 dB, which is higher than the value for TGG crystal (35 dB). It was possible to further minimize the Faraday isolator device.
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