Organic dye-based distributed feedback (DFB) lasers are widely tunable laser light sources in the visible wavelength range and exhibit low-cost, simple fabrication, low threshold and single-mode emission. Precise emission wavelength modeling is essential for understanding and optimization of DFB lasers. Here, a simple yet precise model for calculating the emission wavelength of multilayer DFB lasers is presented. It is found that experimental and calculated wavelength values are in compelling agreement for hybrid nanoimprinted Ormocomp-TiO2 (doped with Pyrromethene 597) first order DFB lasers [1]. Applying the model, the occurrence of different laser light polarization is explained.

Hybrid Ormocomp-TiO2 second order DFB lasers as highly sensitive refractive index sensors featuring narrow linewidth and thus high quality spectral resolution are explored. Design guidelines for high performance sensing are given and the influences of layer thicknesses and grating period on wavelength and wavelength shifts are discussed in this context [2]. This is used for optimizing the laser sensors towards highest sensitivity and thus lowest detection limits. The additional TiO2 layer can increase the sensitivity by a factor of 5 making the laser sensors competitive with state-of-the-art photonic crystal sensors.

The highly sensitive distributed feedback (DFB) dye laser sensors are applied for label-free high frame rate imaging in one dimension and two dimensions of space without any moving parts and enabling a frame rate of up to 12 Hz . The presence of molecules on the laser surface results in a wavelength shift which is used as sensor signal. Imaging is demonstrated by monitoring of flow and diffusion of small sucrose molecules. The unique DFB laser structure comprises several areas of different grating periods which result in distinct laser emission wavelengths [3]. Imaging in two dimensions of space is enabled by focusing an image of the laser surface with a cylindrical lens onto the entrance slit of an imaging spectrometer.

In addition, single-mode biological second order distributed feedback dye lasers are presented [4]. The active core of these lasers consists of vitamin B2 doped gelatin which is spin-coated onto a nanoimprinted grating structure in low-index polymer. These single-mode biological lasers represent a next step towards all-biological lasers where the resonator is formed from structured biological material. Such devices could be biocompatible and eventually biodegradable laser light sources and laser sensors.
[1] C. Vannahme et al., Appl. Phys. Lett. 101, 151123 (2012).
[2] C. Vannahme et al., Laser Photonics Rev. 6, 1036-1042 (2013).
[3] C. Vannahme et al., European patent application no. 14167484.6 (2014).
[4] C. Vannahme et al., Lab Chip 13, 2675-2678 (2013).

Anders Kristensen

Technical University of Denmark

Appearances