USB Optical Bench Options

What makes the USB spectrometers (USB2000+ and USB4000) so special are the options that allow you to configure the bench for your application. Our Applications Scientists can help you choose the optimum components, or you can follow this guide to choose an entrance aperture size, detector accessories, filters, a grating and more. The diagram below shows how light moves through the asymmetrical crossed Czerny-Turner optical bench, which has no moving parts that can wear or break; all components specified are fixed in place at the time of manufacture.

1	SMA 905 Connector	Light from a fiber enters the optical bench through the SMA 905 Connector. The SMA 905 bulkhead provides a precise locus for the end of the optical fiber, fixed slit, absorbance filter and fiber clad mode aperture.
2	Fixed Entrance Slit (specify slit size)	Light passes through the installed slit, which acts as the entrance aperture. Slits come in various widths from 5 µm to 200 µm. The slit is fixed in the SMA 905 bulkhead to sit against the end of a fiber.
3	Longpass Absorbing Filter (optional)	If selected, an absorbance filter is installed between the slit and the clad mode aperture in the SMA 905 bulkhead. The filter is used to block second- and third-order effects or to balance color.
4	Collimating Mirror (specify standard or SAG+)	The collimating mirror is matched to the 0.22 numerical aperture of our optical fiber. Light reflects from this mirror, as a collimated beam, toward the grating. You can opt to install a standard mirror or a UV absorbing SAG+ mirror.
5	Grating & Wavelength Range (specify grating & starting wavelength)	We install the grating on a platform that we then rotate to select the starting wavelength you’ve specified. Then we permanently fix the grating in place to eliminate mechanical shifts or drift.
6	Focusing Mirror (specify standard or SAG+)	This mirror focuses first-order spectra on the detector plane. Both the collimating and focusing mirrors are made in-house to guarantee the highest reflectance and the lowest stray light possible. You can opt to install a standard or SAG+ mirror.
7	L2 & L4 Detector Collection Lenses (optional)	One of these cylindrical lenses, made in-house to ensure aberration-free performance, is fixed to the detector to focus the light from the tall slit onto the shorter detector elements. It increases light-collection efficiency. The L2 is for the USB2000+; the L4 is for the USB4000.
8	Detector	For the USB2000+ we offer the 2048-element Sony ILX511 linear CCD array detector. For the USB4000, we offer the  3648-element Toshiba TCD1304AP linear CCD array detector. Each pixel responds to the wavelength of light that strikes it. Electronics bring the complete spectrum to the software.
9	OFLV Variable Longpass Order-sorting Filter (optional)	Our proprietary filters precisely block second- and third-order light from reaching specific detector elements.
10	UV2 & UV4 Detector Upgrades (optional)	When selected, the detector’s standard BK7 window is replaced with a quartz window to enhance the performance of the spectrometer for applications <340 nm. The UV2 is for the USB2000+; the UV4 is for the USB4000.

A precision SMA 905 Connector aligns to the spectrometer’s entrance slit and ensures concentricity of the fiber. For an upgrade fee that includes the cost of the custom connector and labor, we will replace the standard SMA 905 Connector with a different connector of your choice. We also offer connector adapters, such as an SMA-to-ST Adapter and an SMA-to-FC Adapter. Please call for details on custom connectors and adapters.

Another option available with a USB4000 user-configured spectrometer is the size of the entrance aperture. Entrance slits are rectangular apertures, 1-mm tall and various widths from 5 µm to 200 µm, with the width determining the amount of light entering the bench. Note that the smallest slit achieves the best optical resolution. (For more on how your slit choice affects optical resolution, click here.) A slit is permanent; it only can be changed by our technicians. You can opt against having a slit, in which case the diameter of the fiber connected to the spectrometer determines the size of the entrance aperture.

We offer longpass absorbing or blocking filters; each filter has a transmission band and a blocking band to restrict radiation to a certain wavelength region for eliminating second- and third-order effects. These filters are installed permanently between the slit and the clad mode aperture in the bulkhead of the SMA 905 Connector.

You can replace standard aluminum-coated reflective mirrors with our proprietary, UV-absorbing SAG+ Mirrors, which increase reflectance in the VIS-NIR and, in turn, increase the sensitivity of the spectrometer. SAG+ Mirrors are often specified for fluorescence. These mirrors also absorb nearly all UV light, which reduces the effects of excitation scattering in fluorescence measurements. Unlike typical silver-coated mirrors, the SAG+ mirrors won't oxidize. They have excellent reflectivity -- more than 95% across the VIS-NIR. The price of the SAG+UPG is $290.

You choose from among 14 gratings for each spectrometer. With each grating, you consider its groove density (which helps determine the resolution), its spectral range (which helps determine the wavelength range) and its blaze wavelength (which helps determine the most efficient range). Click here for your Grating & Wavelength Choices.

Predicted Ranges & Resolutions

See a series of graphs to demonstrate the predicted Range and Resolution of your USB2000+ or USB4000 Spectrometer.

At right is a detector with the L4 lens. This cylindrical lens, made in-house to ensure aberration-free performance, is fixed to the detector’s window to focus the light from the tall slit onto the shorter detector elements. It increases light-collection efficiency and reduces stray light. It also is useful in a configuration with a large-diameter fiber for low light-level applications. An L2 or L4 Detector Collection Lens is $174.

The USB2000+ utilizes the Sony ILX511 linear silicon CCD array detector. Our next-generation USB4000 Spectrometer utilizes the Toshiba TCD1304AP linear CCD array detector, which has some electronic advances over the Sony, such as a user-programmable microcontroller. Both are linear silicon CCD arrays, with an effective range of 200-1100 nm, and with the same dynamic range (1300:1). There are some differences between the detectors. For example, the Toshiba detector achieves better optical resolution. Also, on a per-unit area basis, the sensitivity is about the same. Because the Toshiba detector has an electronic shutter, you can almost never have too much light; the shutter prevents the detector from saturating, making possible analysis of transient events such as laser pulses.

Our OFLV Variable Longpass Order-sorting Filters are applied to the detector’s window to eliminate second- and third-order effects. We use patented coating technology to apply the filter onto the substrate. In fact, we are the only miniature spectrometer manufacturer to offer “clean” first-order spectra. There are two OFLV Filter options available for the USB4000 Optical Bench -- the DET4-350-1000 and DET4-200-850 Detectors.

When you specify a detector with the UV2 or UV4 Detector Window Upgrade, we replace the detector’s standard BK7 window with a quartz window to enhance the spectrometer‘s performance from 200-340 nm. The UV2 is available in the USB2000+ Optical Bench with the DET2-UV Detector. The UV4 is available in the USB4000 Optical Bench with the DET4-UV and DET4-200-850 Detectors.

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