Laser action in solution-processed gain media

In this thesis, we study laser action in solution-processed gain media, in which 'conventional' (distributed-feedback, DFB) and 'random' (multiple scattering) lasing are covered, using colloidal quantum dots (CQDs) and organic semicon- ductors. For CQD-based laser action, we demonstrated a flexible DFB CQD laser. A submicron-scale passive bendable grating structure was fabricated, followed by drop-coating a CdSe/ZnS CQDs layer to form the active region. Such a D FB CQD laser has a threshold of 4 mJ / cm 2 and operates in transverse electric polarized multiple-modes. The lasing emission can also be changed in a 610-640 nm spectral window simply by using different sizes of CQDs. We also report CQD random lasing in CdSe/ZnS CQDs deposited into rough micron-scale grooves fabricated on the surface of a glass substrate. The lasing threshold is about 25 mJ / crrr' and stability of the lasing mode positions are anal- ysed from the recorded single-shot spectra and the corresponding power Fourier transform spectra. For polymer-based laser action, a free-standing organic composite membrane DFB laser was demonstrated. In this case, we incorporated an organic semicon- ductor polymer (BBEHP-PPV) as the gain element in a polymer matrix to form an active organic composite, the optical gain and loss characteristics of which are measured. An active grating structure was fabricated, which successfully supported lasing emission centred at 521 nm with a threshold of 1.1 mJ / cm 2. Random laser action in a semi conducting polymer has also been investigated. We found that it is possible to modify the lasing emission wavelength of a photonic glass-based disordered organic gain system over a 7-nm waveband. The emission wavelength is shifted by changing the size of the spheres in the nano-scale range, thereby altering the transport mean free path, and/or by varying the pump spot size and pump fluence.EThOS - Electronic Theses Online ServiceGBUnited Kingdo