Chalcogenide Glass Mid-IR Acylindrical Lens Development

ABSTRACT: Laser source technology in the mid-infrared region, 2um to beyond 10um, is progressing rapidly. Quantum cascade laser (QCL) is one of these new sources, which cover the whole mid-infrared spectrum with high-power and good wall-plug efficiencies. Due to the micron sized and non-circular cross-section of the active region, the laser beam quickly diverges in the direction perpendicular to the plane of the active region (fast axis), while slowly diverging in the parallel direction. As such, it is a necessity for many applications to first collimate the fast-axis direction with high numerical aperture (NA~0.8) and short focal length (f~2mm) micro-lenses. Cylindrical micro-lens with an aspheric contour provides high NA and small focal length, but such lenses are not known to exist presently for mid-infrared. Chalcogenide glasses are a suitable material for the production of micro lenses; these are transparent from 1um to beyond 10um and offer high refractive index, low and negative dn/dT and high damage threshold. Additionally, it is suitable for high-precision molding. The proposed work will demonstrate the feasibility to develop chalcogenide glass acylindrical micro-lenses with low absorbance and high damage thresholds. Prototypes will be made with short focal length (f~1mm) and high NA (~0.8) for 4.6um wavelength. ; BENEFIT: Development of new chalcogenide glass lenses will benefit military applications that utilize mid-wave infrared (MWIR) laser sources capable of deliver high output powers. High-energy pulsed laser made from Fe:ZnSe delivers beam at 4.5um and is pumped at 3um. This laser would need optics with high damage thresholds and transparent in the MWIR. Also, quantum cascade lasers (QCLs) offer wavelengths from 4.5um to beyond 10um and require high numerical aperture cylindrical micro-lenses to collimate the fast axis of the laser. Both of these laser systems would greatly benefit from chalcogenide glass lenses. Chalcogenide glass offers low-loss transmission in the MWIR and beyond, it possess a high damage threshold and can be molded with high precision. The proposed development of chalcogenide micro-lenses will focus on covering the need of the fast axis collimation of single QCL sources. However the chalcogenide cylindrical microlens can also be extended to collimate QCL arrays. Additionally, industrial and medical applications with laser sources working in the MWIR will find benefit in the development of new chalcogenide microlenses.