| Distributed Feedback Lasing in a Dye-Doped Chiral Smectic C Liquid Crystal |
| Distributed feedback lasers (DFBL) are devices that do not use a mirror cavity to provide feedback to a system with gain in order to produce lasing. Rather, DFBL use feedback from the lasing medium itself. The advantage of this device over conventional lasers is its compact size and tunable wavelength output. |
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Feedback
The Chiral Smectic C (SmC*) phase possess a helical superstructure forming a 1-D periodic structure, where the periodicity is temperature dependent. As a result, circularly polarized light propagating parallel to the helical axis is selectively reflected if it has the same handedness as the liquid crystal structure and its wavelength is approximately equal to the pitch. This is the feedback mechanism in this system. |
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Gain
In this experiment cells 50 m m thick were filled with a dye-doped SmC* material that was aligned homeotropically. Dye gives this system gain. |
Lasing
By overlapping the red edge of the photonic band gap with the florescence of the dye, the spontaneous emissions are reduced while stimulated emission are enhanced. This, plus the feedback and gain, make lasing possible.
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