IOP PUBLISHING PHYSICA SCRIPTA Phys. Scr. T135 (2009) 014047 (4pp) doi:10.1088/0031-8949/2009/T135/014047 Inﬂuence of chemical processing on the imaging properties of microlenses Darko Vasiljevi´ c, Branka Muri´ c, Dejan Panteli´ c and Bratimir Pani´ c Institute of Physics, Pregrevica 118, 11080 Belgrade-Zemun, Serbia E-mail: darko@phy.bg.ac.yu Received 8 January 2009 Accepted for publication 12 January 2009 Published 31 July 2009 Online at stacks.iop.org/PhysScr/T135/014047 Abstract Microlenses are produced by irradiation of a layer of tot’hema and eosin sensitized gelatin (TESG) by using a laser beam (Nd:YAG 2nd harmonic; 532nm). All the microlenses obtained are concave with a parabolic proﬁle. After the production, the microlenses are chemically processed with various concentrations of alum. The following imaging properties of microlenses were calculated and analyzed: the root mean square (rms) wavefront aberration, the geometric encircled energy and the spot diagram. The microlenses with higher concentrations of alum in solution had a greater effective focal length and better image quality. The microlenses chemically processed with 10% alum solution had near-diffraction-limited performance. PACS numbers: 42.70.Gi, 81.05.Zx, 42.30.Lr, 42.15.Fr (Some ﬁgures in this article are in colour only in the electronic version.) 1. Introduction Both the production and applications of microlenses are fast advancing, because they are increasingly used in biomedical and general optics. Microlenses can nowadays be found in cellphone cameras and medical devices, and are used in optical data storage, confocal microscopy and wavefront sensing [1–5]. Microlenses can be convex or concave and can have spherical or aspherical proﬁles [6, 7]. Standard dimensions for microlenses range from several tens of micrometers to 1 mm. In this paper, the inﬂuence of chemical processing on the imaging properties of microlenses is studied. Microlenses are produced on a layer of tot’hema and eosin sensitized gelatin (TESG); tot’hema is a drinkable solution used in medicine for curing iron deﬁcit in humans and eosin is an organic dye, with the absorption maximum in the green part of the spectrum, used in medicine, too. A detailed description of the procedure for preparing a TESG layer is given in [8]. Microlenses are produced by irradiating a 100 μm thick TESG layer with an unfocused 2nd harmonic Nd:YAG laser (532nm). The power of the laser beam was 70 mW and the exposure time was 10 s. The details of an experimental setup for the production of microlenses are given in [9]. All microlenses obtained in this experiment are concave with a parabolic surface proﬁle in the central part (80% of the aperture). This fact was veriﬁed by stylus proﬁlometry (Talystep TM surface proﬁler, Taylor– Hobson Ltd) [9]. The TESG layer is unstable, and if it is left chemically unprocessed, it becomes opaque after a few days due to crystallization. In order to prevent crystallization of the TESG layer, microlenses are chemically processed with isopropyl alcohol or various concentrations of an alum solution. In this paper, ﬁve microlenses are presented. The ﬁrst one was chemically processed with isopropyl alcohol, and the other microlenses were chemically processed with the following concentrations of alum solution: 1.25, 2.5, 5 and 10%. The different concentrations of the alum solution change the microlens proﬁle by varying the radius of curvature. Basic geometrical parameters like the effective focal length and numerical aperture depend on the radius of curvature. So, by changing the concentration of alum solution, we were able to obtain microlenses with various effective focal lengths. 2. The geometry of microlenses In this paper, the imaging properties of ﬁve concave microlenses with a parabolic proﬁle are discussed based on the experimental results. The parabolic proﬁle of microlenses is deﬁned for the purpose by the even asphere [10]. The basic 0031-8949/09/014047+04$30.00 1 © 2009 The Royal Swedish Academy of Sciences Printed in the UK