Abstract
We demonstrate microfluidic laser intra-cavity absorption spectroscopy with mid-infrared lambda approximately 9mum quantum cascade lasers. A deepetched narrow ridge waveguide laser is placed in a microfluidic chamber. The evanescent tails of the laser mode penetrate into a liquid on both sides of the ridge. The absorption lines of the liquid modify the laser waveguide loss, resulting in significant changes in the laser emission spectrum and the threshold current. A volume of liquid as small as ~10pL may, in principle, be sufficient for sensing using the proposed technique. This method, similar to the related gas-phase technique, shows promise as a sensitive means of detecting chemicals in small volumes of solutions.
Highlights
Mid-infrared quantum cascade lasers (QCLs) have recently become a mature technology providing continuous-wave operation with hundreds of milliwatts of output power at and above room temperature [1]
We demonstrate microfluidic laser intra-cavity absorption spectroscopy with mid-infrared λ≈9μm quantum cascade lasers
In this work we report a microfluidic sensor for detecting chemicals in small volumes of solutions based on laser intra-cavity absorption spectroscopy (ICAS) using a λ≈9 μm QCL
Summary
Mid-infrared (mid-IR) quantum cascade lasers (QCLs) have recently become a mature technology providing continuous-wave operation with hundreds of milliwatts of output power at and above room temperature [1]. The emission wavelength of these devices can be adjusted by changing the width of semiconductor quantum wells and spans continuously from 3.4 to 24 μm [2], covering the entire mid-IR fingerprint region [3] This allows one to use QCLs for a variety of chemical sensing applications, including gas [4,5] and liquid [6,7,8,9,10] sensing. Quantum cascade lasers can be designed with a very large homogeneously broadened gain bandwidth, with full width at half maximum (FWHM) of ~300cm-1 [20,21] This is significantly larger than a typical FWHM of the absorption lines of liquids in mid-IR (~20 cm-1) and may make sensitive microfluidic ICAS possible [11]
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