Nonlinear optical microscopy with achromatic lenses extending from the visible to the mid-infrared

Adam M Hanninen,Eric O Potma

doi:10.1063/1.5111406

Abstract

With the advent of near-infrared broadband sources stretching into the mid-infrared (MIR) region, there is a growing demand for optical components with utility over an increasingly broad spectral range. For refractive lenses, color correction over such broad bandwidths can be a challenge. In this work, we discuss and demonstrate a two-element lens design with achromaticity spanning the visible to the mid-infrared. The air-spaced doublet designed from commercially available materials shows a significant reduction in spot size and chromatic shift compared to single lens alternatives. We have tested these new broad bandwidth achromats for the purpose of laser-scanning sum-frequency generation microscopy, confirming their improved performance for nonlinear optical imaging applications. The super broadband achromatic lenses represent an attractive alternative to reflective components in ultrabroadband applications, as they enable compact transmission-based optical designs and good focusing performance at off-axis field angles.

Highlights

The ability to generate high-brilliance, coherent mid-infrared (MIR) radiation has improved significantly over the past decade
A case in point is nonlinear optical (NLO) microscopy based on MIR light to excite selective molecular vibrational modes and visible/near-infrared (NIR) light for probing the excited vibrations
We have presented a cost-effective solution to ultrabroadband focusing of light based on CaF2:sapphire achromatic lenses

Summary

Introduction

The ability to generate high-brilliance, coherent mid-infrared (MIR) radiation has improved significantly over the past decade. A case in point is nonlinear optical (NLO) microscopy based on MIR light to excite selective molecular vibrational modes and visible/near-infrared (NIR) light for probing the excited vibrations. Both photothermal MIR microscopy and sum-frequency generation (SFG) microscopy are based on this principle, which makes it possible to probe MIR-driven spectroscopic transitions with conventional visible photo-detectors. Such applications underline the need for optical components that show high performance over an exceptionally wide spectral range. For MIR-based NLO microscopy and other broadband imaging applications, development of super broadband achromatic lens systems is highly desirable

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