Polarization characteristics of a near infrared distributed feedback dye laser operated at the first, second and third orders of Bragg condition

The first, second, and third order distributed feedback lasing characteristics of LDS 759 dye in methanol were investigated. Both intensity modulation and polarization modulation were used to generate laser action. Tunable narrow line-width lasing output was achieved by crossing the pump beams at intersection angles matching the Bragg condition. It was observed that the threshold pump energy increased with the increase of the Bragg order. The ratio of the threshold energy required when using polarization modulation to that required when using intensity modulation increased with increasing Bragg order. The laser output showed different polarization characteristics when the feedback mechanism was changed from intensity modulation to polarization modulation. The degree of polarization of the laser output showed an increasing trend with the Bragg order, which changed from 0.13 at the first Bragg order to 0.67 at the second Bragg order under polarization modulation. Wide-band tuning of the distributed feedback lasing was obtained for first-order operation using both intensity modulation and polarization modulation, from 708 nm to 896 nm and 712 nm to 820 nm, respectively.