Although Raman spectroscopy is an excellent analytical tool, Raman signals are often weak and traditional slit spectrometers typically have poor optical throughput, limiting their effectiveness in low light level setups. Using a high throughput virtual slit design, the Apex 785 Raman spectrometer from Ocean Optics eliminates trade-offs between sensitivity and resolution.

Conventional spectrometers use a narrow entrance slit to achieve high resolution, but at the expense of throughput. The slit can reject as much as 75–95% of the light entering the optical bench. With high-throughput virtual slit (HTVS) technology licensed from Tornado Spectral Systems, Apex spectrometers overcome the compromise between throughput and spectral resolution.

Apex uses a beam reformatting technology that eliminates the need for a physical slit to achieve high resolution. When combined with precision optical coatings, volume phase holographic (VPH) gratings, and solid state detector technology, spectrometer throughput as high as 95% is achievable.

Also, Apex spectrometers use a large input aperture and specially configured optical components to compress, reformat, and then expand the light beam, which narrows the input aperture along the dispersion axis while preserving total flux.

Experimental Conditions

To maintain peak optical throughput, Apex uses a 1200 line/mm VPH grating blazed at 830 nm in an optical bench with an uncooled, NIR enhanced back-thinned CCD array detector.

Raman measurements of paracetamol (acetaminophen), polystyrene, isopropanol, and toluene were made using the Apex spectrometer (APEX-RAMAN-785) in a setup with a 100 mW 785 nm laser diode, a Raman sample holder and a 785 nm Raman fiber optic probe. Integration time intervals ranged from
195 ms for toluene to 750 ms for paracetamol.