Re-evaluation of all-plastic organic dye laser with DFB structure fabricated using photoresists

Organic solid-state lasers (OSSLs) with distributed feedback structures can detect nanoscale materials and therefore offer an attractive sensing platform for biological and medical applications. Here we investigate the lasing characteristics, i.e., the threshold and slope efficiency, as a function of the grating depth in OSSL devices with distributed feedback (DFB) structure fabricated using photoresists. Two types of photoresists were used for the DFB structures: a negative photoresist, SU-8 2002, and a positive photoresist, ma-P 1275. The DFB structure was fabricated using a Lloyd-mirror configuration. The active layer was a rhodamine 6G-doped cellulose acetate waveguide. The threshold for the first order mode (m  = 1) was lower than that for the second and third order modes (m = 2, and 3). A low threshold of 27 μJ cm^-2 pulse^-1 (58 nJ) was obtained using SU-8 2002, with m = 1. The slope efficiency was evaluated as a function of grating depth for each mode and increased as the grating depth increased.