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Spectrometer optics

The fastest and easiest route to a functional spectrometer will be to use one of the current designs.  We have two: The first is designed to measure visible light, the second was designed to cover the ultraviolet and visible, ranging from ~250 to 750 nm.

To build one of our stock designs, you simply need to download the stl files and print them with your 3d printer. 

This page is intended for people who have special requirements and those who really want to get into the weeds with this.

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     The WheeTrometer is a miniature UV-vis spectrometer with a crossed Czerny-Turner configuration.

 

A good description of the Czerny Tuner optical bench is provided by B&W Tek.  As shown in the figure to the right, light enters the spectrometer through the slit (bottom) and passes to the collimating mirror which reflects it to the grating.  After striking the grating, the diffracted light is reflected to the focusing mirror and then on to the detector. 

   To build a WheeTrometer, you will need 3D printed parts, an optical package (containing the mirrors, grating and slit), electronic hardware, and software.  The WheeTrometer project is intended to make all of these things available to educators, researchers and hobbyists from a single site.  The optical elements we sell and our 3D printable mounts and housings were designed to work together.  STL files for printing these parts can be found at our GitHub page.  

Instructions for assembling the optical components are provided on another page of this site.

Stuff on this web site has limited availability.  We just do not have the cash to stock stuff we may not be able to sell.

The optics kit
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One factor that limits a spectrometer's wavelength resolution is the width of the optical slit: Narrower slits give higher resolution.  Our optical slits have a 0.1 mm width.  If you wish to, you can purchase a narrower slit from a commercial source like this one.  If you decide to go that way, be prepared to spend considerably more.  You will also need to modify the slit mounting, but that is something I will help you with.

 

Optical elements used in the WheeTrometer are shown on the above right.  They include the optical slit (front, center), collimating mirror (right), diffraction grating (left) and focusing mirror (back). 

The colimating mirror is 20 mm in diameter with a focal length of 100 mm.  The focusing mirror is rectangular, 20 x 50 mm.  We offer focusing mirrors with either a 50 mm focal length or a 75 mm focal length.  Light dispersion incorporates a 13 mm square reflection grating.  Gratings with a number of line densities are commercially available.  We currently have a few in stock at 1200 and 600 lines/mm.

Modifying the design

You can modify the optical geometry by changing the parameters in the OpenSCAD file, as described in the video below.  This will allow you to customize a spectrometer to meet your requirements.

The physical dimensions of the spectrometer can be easily changed to meet your requirements: Changing the angle between the grating and the focusing mirror will affect the wavelength range you observe, and changing the grating or the focal length of the focusing mirror will change the dispersion and also the optimal grating angle.  The video to the right shows how to change parameters in the  design geometry using the free CAD program OpenSCAD.  The original design file is found in our GitHub page.

Gratings and Grating Angle

One big benefit of adopting the open source spectrometer is that you can modify the hardware design.  The easiest place to do this is at the diffraction grating.  Our visible spectrometer use a 1200 line / mm grating with a 500 nm blaze angle. This gives a wide dispersion angle and a maximum efficiency at a 500 nm wavelength.  By choosing a grating with a lower line density, you can take in more spectrum. You can also get more dispersion by choosing a focusing mirror with a longer focal length.

 

The grating is what gives you wavelength dispersion.You can change the starting point by changing the angle of the grating, which can be done by changing the inner grating mount.

You can purchase gratings with 300, 600, or 1200 lines per mm and blaze angles for maximum efficiency with light between 300 and 1000 nm.  These can be purchased from Thor labs.  Make sure you purchase a ruled reflective grating that is 12.7 mm square to fit the grating mounts.  You might also want to read the grating tutorial Thor has and adjust the grating angle accordingly.

   

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Fiber optic connections
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Fiber optics are frequently used to connect spectrometers to other pieces of equipment, such as sample cells and light sources.  Many of these use SMA905 connectors.  It is possible to interface the WheeTrometer with other fiber optic elements.  To do this, you need a threaded flange, a lens, a spacer and a mount.  Be aware that the thread on the flange is 1/4" 36 threads per inch, which is not a standard that you will commonly find in a hardware store. 

  We can provide flanges and fused silica ball lenses appropriate for uv-vis spectroscopy.  We purchase our flanges and lenses from sources on Aliexpress.  The photo below to the left shows a fiber optic cable interfaced with the instrument.  The figure below and to the right is a screenshot showing flanges available from a vendor on Aliexpress.