ABSTRACT
CONTENTS 5.1 Introduction ........................................................................................... 204
5.1.1 Amplified Spontaneous Emission .......................................... 207 5.1.2 Super-radiance and Superfluorescence.................................. 207 5.1.3 Cavity-Based Lasers ................................................................. 208 5.1.4 Random Lasers .......................................................................... 209 5.1.5 Experimental Setup for Studying Laser Action ................... 210
5.2 Laser Action in p-Conjugated Polymers ............................................211 5.2.1 Amplified Spontaneous Emission in
Solutions and Thin Films of DOO-PPV ................................. 212 5.2.1.1 Spectral Narrowing in Dilute DOO-PPV
Solutions ...................................................................... 213 5.2.1.2 ASE in DOO-PPV Films with Superior
Optical Confinement ..................................................214 5.2.1.3 Transient ASE Dynamics in DOO-PPV Films ....... 218
5.2.2 Cylindrical Microlasers of DOO-PPV .................................... 223 5.2.2.1 Microring Lasers ........................................................ 223 5.2.2.2 Microdisk Lasers ........................................................ 227
5.2.3 Random Lasers in Films and Photonic Crystals .................. 231 5.2.4 Superfluorescence in Organic Gain Media ........................... 238
5.2.4.1 Spectral Narrowing in DOO-PPV Films with Poor Optical Confinement ........................................ 240
5.2.4.2 Superfluorescence in DSB Single Crystals .............. 242 5.3 Summary ................................................................................................ 244 Acknowledgments ......................................................................................... 245 References ........................................................................................................ 245
Organic laser materials have a long history. Lasers based on dye molecules have been a staple of laser science since the 1960s [1,2], with rhodamine the prototypical example. The molecules are optically excited with an external source, placed in a resonator cavity, and readily produce laser emission. The critical feature of the dye molecules that allows efficient laser emission is the chemical nature. In many dyes, this is an alternating p-electron single and double binding of the carbon atoms, whereas the sigma bonds add to the molecule stability. When optically excited, a bound electronhole pair is formed, which is an exciton. From dipole selection rules of quantum mechanics, the excited exciton is a singlet. The conjugated structure allows the exciton to extend over several atoms, and this configuration increases the exciton lifetime and dipole moment, which are crucial for lasing. The increased lifetime allows for population inversion, and the strong dipole moment promotes laser emission.
