Blue surface-emitting distributed feedback lasers based on TPD-doped films Eva M. Calzado, 1,2 Jose M. Villalvilla, 1,3 Pedro G. Boj, 1,4 Jose A. Quintana, 1,4 Pablo A. Postigo, 5 and María A. Díaz-García 1,3, * 1 Instituto Universitario de Materiales de Alicante (IUMA), Universidad de Alicante, 03080 Alicante, Spain 2 Departamento de Física, Ingeniería de Sistemas y Teoría de la Señal, Universidad de Alicante, 03080 Alicante, Spain 3 Departamento de Física Aplicada, Universidad de Alicante, 03080 Alicante, Spain 4 Departamento de Óptica, Universidad de Alicante, 03080 Alicante, Spain 5 Centro Nacional de Microelectrónica, Consejo Superior de Investigaciones Científicas, Isaac Newton 8, PTM Tres Cantos, 28760 Madrid, Spain *Corresponding author: maria.diaz@ua.es Received 28 September 2009; accepted 24 November 2009; posted 15 December 2009 (Doc. ID 117696); published 15 January 2010 Single-mode second-order distributed feedback (DFB) lasers with low threshold, based on polystyrene films doped with 30 wt: % of the hole-transporting organic molecule N,N 0 -bis (3-methylphenyl)-N,N 0 - diphenylbenzidine (TPD) are reported. The laser emission wavelength was tuned between 415 and 427 nm by film thickness variation. The effectiveness of the DFB grating in improving the laser perfor- mance is evidenced by the observation of linewidths and laser thresholds lower than those of the amplified spontaneous emission characteristics shown by films without gratings. The use of holographic lithography as the technique for grating recording has allowed us to prepare large samples in a fast, versatile, and simple manner. © 2010 Optical Society of America OCIS codes: 140.0140, 140.2050, 140.3580, 160.0160, 160.3380, 160.4890. 1. Introduction Since the discovery of stimulated emission in semi- conducting polymer films [1–3], extensive research has been devoted to the development of solid-state lasers based on semiconducting materials, including polymers, small organic molecules, oligomers, and dendrimers [4–6]. A very unique property of organic materials is that, due to their broad photolumines- cence (PL) spectrum, the laser wavelength can be tuned over a wide range [7]. Among the various types of organic material, those that are semiconducting open the possibility of electrical pumping. Moreover, those that are soluble have the additional advan- tages of easy processing in the form of thin films by inexpensive techniques and high compatibility with the substrates over which they are deposited. These characteristics open ways to heterogeneous integration of optic and electronic devices. One of the main challenges in the use of new active organic materials for lasing is the achievement of laser thresholds, low enough to allow pumping with com- pact and inexpensive optical sources [8–10]. The easiest way to evaluate the potential of a cer- tain material to be used as an active laser medium consists in characterizing its amplified spontaneous emission (ASE) when deposited as thin films in a waveguide configuration [2,11]. In addition, this technique is the most convenient for comparing the performance of different materials, since it allows se- parating the variations due to the material from those due to the resonant cavity. The laser properties of 0003-6935/10/030463-08$15.00/0 © 2010 Optical Society of America 20 January 2010 / Vol. 49, No. 3 / APPLIED OPTICS 463