IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 14, NO. 5, SEPTEMBER/OCTOBER 2008 1323 Progress on the Photoresponse of Chalcogenide Glasses and Films to Near-Infrared Femtosecond Laser Irradiation: A Review Laeticia Petit, Nathan Carlie, Troy Anderson, Student Member, IEEE, Jiyeon Choi, Student Member, IEEE, Martin Richardson, Senior Member, IEEE, and Kathleen C. Richardson, Life Member, IEEE (Invited Paper) Abstract—This paper reviews ongoing progress in exploring the mechanistic origins of photoinduced structural modification in chalcogenide glasses (ChGs). These findings, reported by groups at the University of Central Florida, Clemson University, and throughout other research programs within the United States and abroad, have examined the relationship between the network mod- ification and other photoresponse of IR glasses upon exposure to near-infrared (NIR) femtosecond laser exposure. Contained is a review on the principles of femtosecond laser writing in glass, the photoinduced phenomena, and a summary of the main models predicting photoinduced material response. We compare the pho- toresponse of As- and Ge-based films, taken as example, follow- ing NIR femtosecond laser irradiation that results in near-surface photoexpansion and an increase or decrease of the refractive index, respectively. This difference in photoresponse has been related to the “layered” network of the As-based glass that leads to the break- ing and formation of bonds during laser exposure as compared to the 3-D network of Ge-based glass that leads only to a modifica- tion of the bond arrangements. Last, an explanation of the need to control the photoresponse of ChGs by aging, changing the glass thermal history, adding modifiers, or replacing the anions forming the network is discussed. Index Terms—Chalcogenide glasses (ChGs), femtosecond near- infrared (NIR) laser irradiation, micro-Raman spectroscopy, pho- toexpansion, photosensitivity, refractive index modification. I. INTRODUCTION C HALCOGENIDE glass (ChG) materials have been stud- ied extensively over the past 50 years. Along with the growing interest in these materials for optoelectronic and telecommunication applications, comes a need to understand Manuscript received January 8, 2008; revised February 13, 2008. First published May 14, 2008; current version published October 3, 2008. This work was supported in part by the National Science Foundation and in part by the Cen- ter National de la Recherche Scientifique (CNRS) under Grant ECS-0225930, Grant ECS-0123484, Grant INT-0129235, Grant DMR-9912975, Grant DMR- 0312081, Grant DMR-0321110, Grant EEC-0244109, and Grant NSF/CNRS 13050. L. Petit, N. Carlie, and K. C. Richardson are with the School of Mate- rial Science and Engineering, Center for Optical Materials Science and En- gineering Technologies (COMSET), Clemson University, Clemson, SC 29634 USA (e-mail: lpetit@clemson.edu; ncarlie@clemson.edu; richar3@exchange. clemson.edu). T. Anderson, J. Choi, and M. Richardson are with the College of Op- tics and Photonics, Center for Research and Education in Optics and Lasers (CREOL)/Florida Photonics Center of Excellent (FPCE), University of Central Florida, Orlando, FL 32816 USA (e-mail: troy@creol.ucf.edu; jichoi@creol. ucf.edu; mcr@creol.ucf.edu). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JSTQE.2008.922898 any modification or variation in these properties resulting from light irradiation. Photoinduced structural changes in amorphous chalcogenide films have been broadly investigated for more than 30 years [1], [2], but the mechanistic origin behind these changes is not identical to all ChGs, nor fully understood. One interesting consequence of the interaction of tightly focused femtosecond laser radiation within transparent materials is the possible mod- ification of the structure and of refractive index of the exposed area under specialized experimental conditions. These photo- and thermally induced effects may be either irreversible or re- versible. This is of particular interest for writing 3-D structures in a wide variety of glasses for applications, such as optical memories, holography, imaging, photolithography [3], density information storage, high-resolution display devices, and fabri- cation of diffractive optical elements [4]. Most of the data published on ChG–laser interactions to date have been mainly focused on amorphous (a-) Se, amorphous or crystalline As 2 S 3 , or As 2 Se 3 [5]. Few efforts have systemati- cally examined the photoresponse of Ge-based ChGs [6]–[15] or multicomponent (>binary) As-containing materials. These studies demonstrated that these amorphous chalcogenide ma- terials, based on binary (e.g., As–S, As–Se) or ternary [e.g., Ge–As–(S, Se), Ge–Sb–(S, Se)] combinations, exhibit a wide variety of physical and chemical changes when illuminated by bandgap or IR light as the photoinduced changes are due to transformations of the structure and impact many related phys- ical properties. Often new materials are developed without suitable aware- ness as to how key physical properties and performance may be compromised following laser interaction. For the last decade, our effort has been focused on acquiring a greater understand- ing of the mechanisms behind ChG–laser interaction realized during laser material processing, with a focus on developing specific understanding of composition-dependent response that will allow predictive processes, whereby, new materials or mor- phologies, with enhanced functionality and known stability, can be engineered [6], [16], [17]. A large number of models has been proposed since the first developed in 1977 by Street [18]. These models, which most of them are reviewed in Section V, are based on the suggestion that bonds get broken and rearranged, while others propose that these bonds are left unchanged while various modifications of the coordination spheres (and residual charge/defects) take place. 1077-260X/$25.00 © 2008 IEEE