Interesting experiments of all kinds (inside and outside the bounds of rigorous academic work) executed over the years are journaled here.
2019-2020: Data-logger for measuring ambient parameters around a Raman spectrometer¶
Custom developed Raman spectrometers are exposed with light propagating through open space (sometimes over long distances). For the present case, the target was to study the stability of obtained Raman spectra on a custom developed Raman spectrometer. In order to assess the extent of change of ambient conditions, a miniature data-logger based on Arduino was developed with software interface to LabVIEW on a Windows PC. This data logger measured temperature at three different points on the optical table, along with atmospheric humidity and pressure (inside the data logger), and sent this data over the serial interface (RS-232) to be read by a LabVIEW VI.
The main LabVIEW VI which read data from the data-logger also sampled temperature and wavelength information from a wavelength meter, as well as the laser power from a power meter after ADC conversion. See figure below showing the Arduino at the heart of the unit.
The data flow is shown below.
Temperature measurement at the polychromator slit and near laser head - connected to Arduino
PT100 3-wire RTD with MAX31865 amplifier from Adafruit, with SPI communication (accuracy \(\pm\) 0.15K, precision \(\pm\) 0.2K). Accuracy was checked in the lab using ice and boiling water.
Ambient humidity and pressure measurement - connected to Arduino
BME280 (sensor from Bosch) mounted on IC unit by Adafruit, with SPI communication was
used with Arduino. This sensor has accuracy of \(\pm\) 3% for relative humidity and \(\pm\) 1hPa for
pressure.
Arduino AT-Mega2560 microcontroller
This microcontroller was housed in a lab made box and connected to a miniature display.
Communication with other sensors was made with protocols mentioned for each sensor. After
averaging 10 measurements, this device wrote the results on the Serial out which was read
by the LabVIEW VI.
Laser wavenumber measurement - connected to PC
Wavelength meter (HighFinesse, WS7) was interfaced with LabVIEW program allowing sampling of the laser wavenumber, feedback voltage to laser for stabilization of wavelength and the internal temperature.
Laser power measurement - analog output measured by NI-DAQ
Power was measured via GentecEO power meter (TPM 300 CE) equipped with UP19K-15S-
H5-D0 thermopile sensor. Analog voltage output from the power meter was readout using Data
Acquisition (DAQ) device (PCI-6281, National Instruments) which was interfaced to the main control LabVIEW VI.
The resulting dataset from the main VI was as follows:
Temperature sensor (PT100 3-wire RTD connected to MAX31865) unit is pictured below.
The MCP sensor is pictured below.
Overall housing of the sensor unit.
Eventually the acquired temporal data on ambient conditions were correlated with Raman spectral changes. The results were analyzed looking at variations in Raman band positions of benzene and emission lines of neon. See Link: <https://doi.org/10.1002/jrs.6085> for more details.
2016: Using sun-light to observe Raman scattering¶
In this set of experiments, we attempted to use the blue portion of the sunlight to generate Raman scattering from liquid sample and observe this scattered light in the green to yellow region.
A set of filters were used for this purpose. Short-pass filter was used for obtaining light in the blue region (from 350 to 400 nm) and a long pass filter was used before the detector to look only at the scattered light at higher wavelengths.
To prevent any ambient light passing to the cellphone’s camera (used as detector), a box housing was used in which the filters, sample and the camera were placed. Sunlight was focused using a magnification lens. The sample chamber was further isolated in a dark area. It was covered in , with only blue light entering from a small aperture, which is perpendicular to the detection-optical-axis. Concentrated solution of napthalene in benzene was used as the sample.
Tight focusing with a plano-convex lens followed by the short-pass filter produced fairly intense blue light (this was in peak of summer in Hsinchu, Taiwan). An ordinary magnification glass was used as the lens.
For the detector, a cell phone’s camera was used. Optical image was acquired across a dark background, shown below. The recorded image did not include any Rayleigh scattering (which would be in blue) but comprised of yellowish beam, only faintly observable with human eyes. This would be Raman scattering along with some fluorescence. The image was acquired using a cell phone camera with manually settings. Exposure time of 0.1 s and ISO of 200 was used.
Acknowledgements: Prof. Hiro-o Hamaguchi and Dr. Masahiro Ando
