Abstract
Organic solid-state lasers (OSSLs) with distributed feedback (DFB) structures or distributed Bragg reflectors (DBRs) are promising for potential application in bio-sensing and hazardous materials detection. Here, the laser performances of the all-organic DFB waveguide lasers with various grating heights ranging from 0.4 to 4.7 μm were investigated. The grating structures used as the lasing cavity were fabricated using a two-photon absorption (TPA) direct laser writing (DLW) method with an SU-8 negative photoresist. The laser active layer consisted of a rhodamine 6G (R6G) laser dye and a cellulose acetate (CA) matrix. The R6G/CA solution was spin-coated onto the quartz substrate with the cavity (grating) structures to fabricate the DFB waveguide laser devices. The diffraction order of lasing ranged from m = 4 to 7. As the grating height was increased to 1.9 μm, the slope efficiency increased for all diffraction orders and the threshold decreases for each diffraction order. The dependence of the cavity (grating) length on the laser performances was investigated. The slope efficiency increased as the cavity length increased to 300 μm. The effect of the cavity (grating) position on the slope efficiency and the threshold position of the cavity (grating) was also studied. A maximum slope efficiency of 10.2% was achieved for the DFB waveguide laser device with a cavity (grating) length of 300 μm, a cavity position at 6 mm from the emission edge of the waveguide, and an aspect ratio ≈3 between the grating height of 1.74 μm and the grating width of 0.6 μm for the diffraction order m = 6 for lasing.
Highlights
In our previous report[8], the dependence of the grating height less than 80 nm on the threshold and the slope efficiency for lasing were investigated for the various orders of the diffraction process (m) ranging from m = 1 to 3; it was found that the slope efficiency increases with increasing grating height, and lower threshold was measured for lower diffraction orders
The effects of grating height, cavity length, and grating position on the laser performances of the threshold and the slope efficiency were investigated for the distributed feedback (DFB) laser waveguide devices consisting of the grating structures of an SU-8 negative photoresist and a laser active layer of the rhodamine 6G (R6G)-doped cellulose acetate (CA)
The SEM images clearly show that the proper grating structures for the laser cavity are formed using a SU-8 negative photoresist
Summary
Received: 7 May 2019 Accepted: 10 July 2019 Published: xx xx xxxx by a Two-Photon Absorption DLW Method. The grating structures used as the lasing cavity were fabricated using a two-photon absorption (TPA) direct laser writing (DLW) method with an SU-8 negative photoresist. The R6G/CA solution was spin-coated onto the quartz substrate with the cavity (grating) structures to fabricate the DFB waveguide laser devices. Two-photon polymerization of R6G-doped SU-8 negative photoresists by a DLW method obtained a DFB organic laser device with the grating height of 80 nm and the grating pitch of 550 nm, corresponding to the third diffraction order (m = 3)[19]. The effects of grating height, cavity (grating) length, and grating position on the laser performances of the threshold and the slope efficiency were investigated for the DFB laser waveguide devices consisting of the grating structures of an SU-8 negative photoresist and a laser active layer of the R6G-doped cellulose acetate (CA). An optical-fibre coupled photodiode pyrometer (Ophir PD-10-P) with a Nova II Display equipped with an optical filter to cut out the incident excitation beam was used to monitor the absolute intensity of the laser emission from the edge of the waveguide
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