Laser from a liquid excimer

Abstract

Conjugate Polymers are novel optoelectronic materials with wide range of applications. In this paper, we present the results of fluorescence and laser excited amplified emission spectra of MEH-PPV polymer, which has some surprising laser properties. (MEH -PPV) is a complex macro molecule. When this is dissolved in liquids like, tetra hydro furan (THF), it is very fluorescent, with quantum yield comparable to conventional laser dyes. This polymer has absorption peak around 490nm and emission peak at 560nm for a low concentration (1 micro molar). However for higher concentration (10 micro molar) it has a new band at 600nm, in emission only without any new band in absorption. This is a strong indication of excimer formation. When this particular solution is pumped by a 3rd harmonic of Nd-YAG laser (355nm and 11 ns), the polymer underwent strong excitation and population inversion and amplified spontaneous emission (ASE) at 600 nm only. For lower concentration, we could get fluorescence only with a peak at 560 nm. That is, this particular polymer produces ASE and hence laser only from the excimeric state. It is important note that most of the liquid laser dyes do not produce laser from the excimeric state; other solutions which are easily forming excimeric state do not laze. This appears to be the only liquid excimeric state laser. Another important feature of the solution it is at least 10 times more stable than the conventional laser dyes.