Kirra Faraday Rotators and Isolators for Ti:Sapphire Laser

Lambda, nm	Clear Aperture,	Rod material	Isolation	Model No.
	mm		dB	Rotator
				Isolator
800	5	TGG	38	5AFR-800C
				5AFI38-800C
		Glass	38	5AFR-800G
				5AFI38-800G
	8	TGG	38	8AFR-800C
				8AFI38-800C
		Glass	38	8AFR-800G
				8AFI38-800G

Broadband models have letter B at the end. For example model Kirra 8AFI38-800GB is a Faraday Isolator with 8 mm aperture for 800nm central wavelength made of Faraday Glass with 38 dB isolation

For custom Faraday Rotator or Isolator e-mails us at sales@dmphotonics.com
Please specify the following: wavelength of operation, beam size (required clear aperture), required isolation (38dB and 60dB are our standard).

Del Mar has optimized its new optical isolator, the 5AFI36- 800B broadband Faraday Isolator, to work with femtosecond Ti:sapphire lasers. The device isolates the laser from its own reflections. Its magneto-optical rod is cut from glass (MOS-10), polished to a flatness of L/10, and has a parallelism better than 10 arc•s and a peak isolation of 36 dB. It is antireflection-coated to give a residual reflection of less than 0.2% on each side in the 765- to 835-nm range. The isolator’s polarizers are air-spaced Glan prisms made of calcite. Entrance and exit faces of the polarizers are antireflection-coated to provide a residual reflection of less than 0.3% in the 765- to 835-nm range. request q quote

At high powers optical feedback can damage or disrupt the operation of a laser system. To reduce this feedback, an optical isolator can be inserted into the system. Faraday optical isolators (based on the Faraday effect) are passive unidirectional, nonreciprocal devices that utilize the phenomenon of magneto-optic rotation to isolate the source and protect the laser oscillator from reflections in an optical system. In other words, they basically act as an optical diode allowing the propagation of light in only one direction.

Faraday isolators (see Figure 1) typically consist of a Faraday rotator, two polarizers, and a body to house the parts. The Faraday rotator, in turn, consists of magnetooptically active optical material placed inside a permanent magnet (Nd-Fe-B).

In the Faraday optical isolator shown in Figure 2, the magneto-optical rod (located inside the Faraday rotator) is cut from glass (MOS-10) polished to flatness of

/10, and has parallelism better than 10 arc seconds. It is anti-reflection coated with residual reflection <0.2% (each side) in the 765-835 nm range. The polarizers are air-spaced Glan prisms made of calcite. Entrance and exit faces of polarizers are anti-reflection coated with residual reflection of <0.3% in the range. Polarizer transmittance is >98%. This gives a total transmittance of better than 85% for the isolator.

Laser light (polarized or unpolarized) enters the input polarizer (P1) and is linearly polarized to 0°. Next, the linearly polarized light enters the Faraday rotator rod (magneto-optical rod). The plane of polarization rotates as the light propagates along the axis of the rod. The Faraday rotator is tuned to rotate the plane of polarization by 45°. (Changing the position of the rod allows tuning over a wavelength range from 765-835 nm.) The light then passes through the output polarizer (P2) whose transmission axis is also at 45°.

Any back reflected light re-enters the isolator through the output polarizer and becomes polarized at 45°. The back reflected light then passes through the Faraday rotator, which produces another 45° of rotation, and is now polarized at 90°, or horizontally, before being stopped by the input polarizer, still at 0°. Thus, the laser is isolated from its own reflections that may occur in the application part of the optical set.

This information was contributed by Sergey Egorov for Del Mar Photonics, located in San Diego, CA.

Wideband isolator model Kirra 5AFI38B-800C has 100 nm band: extinction ratio at 750/850 nm - 35dB, at 800 nm - 38 dB.

Isolation of the broadband Faraday isolator Kirra 5AFI38B-800C for femtosecond Ti:Sapphire laser as a function of wavelength.

Transmission of the broadband Faraday isolator Kirra 5AFI38B-800C for femtosecond Ti:Sapphire laser as a function of wavelength.