A Raman microprobe with a holographic beamsplitter is described. The beamsplitter is shown to have 90% laser insertion efficiency and high Raman transmission efficiency on both the Stokes and anti-Stokes side. Useful spectra are obtainable as close as ±60 cm−1 from the exciting line using 4 mW power.

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We describe a ball lens assembly, which functions as a broadly tunable bandpass filter and polarizer with imaging capabilities. The physical basis is resonant tunneling of light through an air gap between two half-ball lenses symmetrically coated by few-layer ( S i / S i O 2 or T a 2 O 5 / S i O 2 ) admittance matching stacks. Tuning is achieved by simultaneous adjustments of the incident angle and the air gap thickness. Individual filters with operational ranges spanning visible ( ∼ 400 − 700 n m ) and near-infrared ( ∼ 1000 − 1800 n m ) wavelengths were assembled using 10 mm diameter lenses. We show that these filters, configured as a stand-alone scanning spectrometer, can provide a resolving power ∼ 100 and f -number ∼ 2.5 for a fiber-compatible input aperture <2019