The ability to provide UV-NIR coverage in a single miniature spectrometer has always been a challenge. Trade-offs inherent to most diffraction gratings – most noticeably, the effect of blaze angle on the efficiency of the diffraction – can pose challenges for certain applications. While gratings were available that diffracted over a wide range, this came at the expense of decreased optical resolution and increased problems associated with second- and third-order overlap.

Newer gratings such as the XR-1 provide good efficiency over a wider wavelength range (200-1050 nm) than is otherwise possible with standard gratings. What’s more, good optical resolution (<2.0 nm FWHM for most setups) can be maintained, and second- and third-order effects are eliminated by applying proprietary filtering technology to the CCD-array detector window. Transmission efficiency is affected only marginally by this filtering.

Broad spectral response in a single spectrometer offers convenience for those who regularly make measurements in both the UV-Vis and Vis-NIR, yet it also offers a solution for applications where samples are responsive across that same broad range. Examples include certain plasmas, solar irradiance, atomic emission lines and broad-range light sources.

Experimental Conditions

To test the response of the XR-1 grating, we installed the 500 lines/mm groove density grating in the optical bench of our USB2000+ Spectrometer. The spectrometer’s optical bench also included a 25 µm slit and order-sorting detector filter. The grating provides 850 nm of spectral range and is blazed at 250 nm.

The test sample for the experiment was our DH-2000-BAL Deuterium Tungsten Halogen Light Source. The DH-2000-BAL combines the continuous spectrum of deuterium and tungsten halogen light sources in a single optical path to produce a powerful, stable output from 215-2000 nm (we observed only the region from 200-1050 nm). A UV-Vis optical fiber collected the signal from the light source. We recommend our QP450-2-XSR optical fiber, which is a 455 µm core diameter fiber with excellent solarization resistance properties. Integration time of 10 milliseconds is typically sufficient for measuring a light source such as the DH-2000-BAL.

Results

The emission spectrum of the UV-NIR light source measured with the USB2000+XR matched the anticipated spectral output. The XR-1 grating showed good efficiency across the 200-1050 nm spectral range, with the best efficiency in the UV. Optical resolution was calculated at ~1.7 nm (FWHM) with a 25 µm slit (the standard slit option for the USB2000+XR) and at ~1.2 nm (FWHM) with a 5 µm slit. Other expected spectrometer performance characteristics were unaffected by the presence of the grating.

Conclusions

Results demonstrate that an Ocean Optics spectrometer configured with the XR-1 extended-range grating will provide spectral coverage across the 200-1050 nm spectral range without sacrificing optical resolution performance or being subject to second- and third-order diffraction effects. The XR-1 is available in the application-ready USB2000+XR, USB4000-XR1 and JAZ-EL200-XR1 Spectrometers (each has a 25 µm slit and order-sorting filter) or as a custom option in one of our other spectrometers. For applications requiring broad range and sub-nanometer optical resolution (FWHM), our HR2000+CG and HR4000CG-UV-NIR composite-grating spectrometers are recommended.

More Online:

- XR-Series Spectrometers