The overall goal of the following experiment is to determine the effects of pulse energy and timing parameters for detection of elements in non conducting materials like soil simulants using laser induced breakdown spectroscopy or lips. This is achieved by focusing a laser pulse onto the soil stimulant to create a plasma. The light from the plasma is spectrally resolved and detected to provide information about the elements in the sample.
As a second step. Atomic emission lines from the spectra in the synthetic silicate samples, which have varying concentrations of trace elements are used to create calibration curves at various energies and timing parameters. Next, the calibration curves are used to determine sensitivities and detection limits for different pulse energies and timing parameters.
Results are obtained that show that lower pulse energies provide similar detection limits to those achieved using higher pulse energies, and that there will be a slight loss in detection capabilities when using non gated mode detection.Made. Advantages of lib's technique include being able to analyze solids, liquids, or gases with little or no sample preparation, providing both quantitative and qualitative analyses, detecting multi elements and needing only optical access to the surface. This makes it ideal for analyses that cannot be carried out in the laboratory.
Currently, libs is being used for many different applications, especially those that require field-based measurements. The system in this video uses a Q switch N-D-Y-A-G laser operating at 1064 nanometers with a pulse frequency repetition rate of 10 hertz.Mirrors. Direct the laser beam to a 75 millimeter focal length lens that focuses the laser pulses on the sample, which is placed on a translation stage.
Collect the plasma light generated by the sample with an optical fiber placed near the plasma formation point to resolve and record the spectrum using a shell spectrograph with an intensified CCD. Use a digital delay generator to control the timing between the laser and ICCD detector. Verify the timing within oscilloscope.
Next, prepare samples for the experiment to mimic common soil samples. Use synthetic silicate certified reference materials with known element concentrations. Use aluminum discs, a D cast set, and a hydraulic press to make smooth 31 millimeter diameter pellets for consistency in the analysis.
As a first step, use the samples to create calibration curves. To collect libs data. Place a sample at the focal point of the focusing lens at the computer.
Check the ICCD settings and for non gated work. Set the time delay to zero microseconds. Change the laser pulse energy to one of the used energies and begin data collection.
After each spectrum is recorded, choose a new spot on the sample for analysis. When all of the non gated recordings are done, change the ICCD time delay to one microsecond for gated detection and record five new spectra With this configuration, repeat the non gated and gated measurements for each of the samples and energies to be tested. Generate the calibration curves by plotting the average area of the peak in the spectrum for an element on the Y axis and the element concentration along the x axis.
Alternatively, plot the ratio of the peak area to the area of the iron peak at 406 nanometers. Along the Y axis, use a linear trend line to fit the calibration curves and find detection limits using three sigma detection to find the temperature of the plasma, identify iron lines in the data with wavelengths between 371 and 408 nanometers, and with known upper energies degeneracy and transition probabilities. These quantities and the intensity of the transition should satisfy this equation and produce a straight line as a function of the upper energy of the transition.
The magnitude of the slope is negative one over kt, where K is boltzmann's constant and T is the temperature. Plot the data and fit the curve to a straight line. Then solve for the temperature here, 8, 400 kelvin to find the electron density of a sample at the focus of the laser system.
Set the ICCD gate width to 4.5 microseconds and the time delay to 0.5 microseconds. Measure the full width that half maximum of the hydrogen line at 656 nanometers. Calculate the electron density using the reduced wavelength and a temperature of 10, 000 kelvin.
This graph generated for detection of barium shows how the two ways to create calibration curves for calculating detection limits compare using gated data with a one microsecond delay. The detection limits calculated using the area the spectral peak are shown in blue and are referred to as un ratioed shown in black are the detection limits calculated by taking the ratio of the area under the spectral peak to the area of the peak under the 406 nanometer line of iron and are referred to as ratioed. The ratio data produces lower detection limits over the pulse energies used in the experiment.
This is also found with non gated data collected with no delay using ratioed data. This plot compares detection limits between gated detection in black and non gated detection in blue over the range of energies for barium. It can be seen that the gated detection mode produces lower detection limits.
This generally applies to all of the data comparison of the spectrum of a sample using gated detection versus a spectrum of the same sample. Using non-G gated detection shows the expected lower baseline of gated detection. These spectra were taken with 10 millijoules pulses for non-G gated detection.
The peak area under the spectral peaks of the elements in the synthetic silicate sample increases as a function of laser pulse energy. The same is seen for gated detection. This increase is most likely due to a greater mass of sample being ablated producing a larger plasma and a stronger excitation signal.
Note the increase in the background as laser pulse energy has increased in this non-G gated measurement. This suggests self-absorption and that an increased plasma continuum background might affect detection capabilities at higher energies. However, overall results show that there was not a significant reduction in detection capabilities using lower pulse energies and non gated detection.
The average temperature as a function of laser energy is seen to be relatively constant over the range of energies tested for both detection modes. However, the non gated mode temperature is in the range of 10, 000 to 11, 000 kelvin, while the gated mode temperature is in the range of 8, 100 to 8, 700 kelvin. This is reasonable since the earliest part of the plasma formation is monitored in the non-G gated mode, the electron density measurement shows a minor increase in the density as the laser pulse energy increased by a factor of 10.
After watching this video, you should have a good understanding of how to successfully perform a lips measurement.It.
