The ”inelastic scattering of light”, or Raman effect, was observed in practice for the first time already in 1928 by C.V. Raman for which he was awarded the Nobel Prize in 1930. Raman spectroscopy has become a popular analytical tool because of its ability to probe nondestructively and provide fingerprint information about materials. Recently, Raman spectroscopy has begun to realize its potential as an almost universally applicable analytical technique, not only in material and life science research applications, but also as a process control tool in, for instance, pharmaceutical, food & beverage, chemical and agricultural industries. The introduction of Raman spectroscopy analysis in the educational curriculum helps the students learn the spectroscopy basics. Furthermore, component-wise familiarization and fabrication training will help the students to evolve their own methodologies to fabricate and customize the instrument for specific applications. Though many Raman spectrometers are commercially available, the high cost (e.g. ￥1 million) makes it unaffordable for most academic institutions.
There are six key parts for Raman instrument: microscope with high quality illumination, stable laser with short line width (e.g. below 0.1 nm), high quality edge filter, high quality spectrometer, deep-cooled CCD and software. How to develop a low-cost Raman setup (e.g. less than ￥ 20,000) but keep high sensitivity (e.g. performance much closed to high end scientific Raman instrument), it is still a big challenge.
There are some features in our home-built laser microscopic Raman spectrometer:
1. We develop 532 nm DPSS laser pointer with our home built constant current source and TEC cooler with temperature control, the temperature sensor is LM35.
2. Spectrometer is based on CCTV lens with 100 mm focal length and 1200 g/mm blazed grating.
3. ILX554B linear CCD detector (2048 pixel, 14 μm x 56 μm) is controlled with our home-built driver, TEC 12706 is used for cooling to reduce dark noise, the temperature sensor is LM35. when cooled temperature near or below zero degree/ 0 °C, the water vapor condensation problem need be solved.
4. The optical shutter is based on servo motor, the variable optical attenuator is based on stepper motor and photoelectric reset sensor.
5. Software.
We used labVIEW to communicate with Teensy 3.2 board /72 MHz, the Teensy board controlled the shutter (based on servo motor) , the laser density filter set (12 step, 100% to 0.05%, base on stepper motor with photoelectric reset sensor), the temperature of laser and CCD, the CCD driver and CCD signal collection.
Below showed some performance with our setup:
the 2TO band (transverse optical phonon, 900-1000 cm-1) can be seen at higher excitation power, as this peak is about 40x weaker than 520 cm-1, its signal is easy buried in thermal background.
This home-built Raman system is under further improvement. For example, (1) the dark current noise of CCD need be further reduced with deep cooling, we just curious how to push the performance of this setup closed to the high-end scientific Raman spectrometer. (2) develop several laser with narrow linewidths (e.g. 1 MHz) and high spectral purity (e.g. 80 dB) based on the stable temperature control. (3) develop more functions.
1st updated time: 2022-06-04
Here is some new result of the performance of our home-built Raman system.
2nd updated time: 2022-11-12