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High Resolution Spectrometer

A novel spectrometer achieves a resolution of about 40pm across the entire visible spectrum, which is between 350nm and 650nm.

This is possible by evaluating the incidenting light on a two dimensional detector. In one direction ("coarse resolution") a transmission grating and/or a prism delivers a resolution of about 0.5nm. Each of those 0.5nm wide spectral intervals is then finely resolved along the second direction by using an etalon ("fine resolution"), which results in up to 20000 spectral channels.

In the following the essential principles of functoning and the results obtained from a joint ZIM-project are presented.

Principle

The principle of the spectrometer is to generate two distinct resolutions (coarse and fine) on a two dimensional image sensor.

Along one of the axes, the incidenting light is fanned out with a relatively coarse resolution of about 0.5nm by using a grating and a prism (left).

Perpendicular to the first axis, the light hits an etalon at varying angles where each spectral range can be broken up much finer (middle and right).

coarse resolution
The coarse resolution delivers horizontally stacked vertical lines of around 0.5nm width each
fine resolution
The fine resolution, here displayed as a pure intensity, vertically distinguishes single frequency bands within each coarse resolution
Browser-GUI
The spectra can be pictured and zoomed down to 1pm by means of a browser

Laboratory Set Up

As of now there is one laboratory set up of the size LxWxH = 55cm x 22cm x 18cm. On the input side it has a slit with adjustable width, which is typically set to 50µm. The camera used is a USB-camera (Type: SBIG ST-8300M/C) with a CCD sensor and 3326x2504 pixles.

breadboard setup
Demonstrator of size 55x22x18cm³
simulative optimization
Simulative optimization of the combination of grating, prism, and etalon
3D model of a prototype
3D model of a prototype

Spectra

As an example, the spectrum of neon is depicted here. The red line shows the resolution through the grating. The resolution resulting, after including the information from the etalon, is depicted in black. Then, for instance, the resolution is 25pm (far right).

Full spectrum of neon
The neon spectrum exhibits a multitude of lines
Magnification
The resolution with etalon is much finer than with the prism/grating only
resolution
The typical resolution of a line lies between 18pm and 42pm

Further Information

  • Project partner: ,
  • Specifications: Spectral range 350-650nm, resolution <50pm
  • Download: poster presentation
  • Publications: September 2014 (68[9]) issue of Applied Spectroscopy (special issue LIBS), pp.1030-1038
  • Project funding: (FKZ: KF2255601FK9)