Directional Emissivity Using Femtosecond Laser Surface Processing

Giovanna M, Castejon-Cruz Author

07/28/2021 Added

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Video presentation for my summer research experience in directional emissivity, with a total of three measured samples processed using a femtosecond laser to increase emissivity values.

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[00:00:01.231]Hello everyone.
[00:00:02.064]My name is Giovanna Marian Castejon Cruz,
[00:00:03.700]I'm from the University of Puerto Rico at Humacao
[00:00:06.030]and I'm here to present my summer research experience
[00:00:09.440]in directional emissivity using femtosecond laser
[00:00:12.200]surface processing under the mentorship
[00:00:14.860]of Dr. Craig Zuhlke and Andrew Reicks
[00:00:17.370]from the Center of Electro-optics
[00:00:19.270]and Functionalized Surfaces.
[00:00:23.290]Emissivity is a measure of the effectiveness
[00:00:25.930]of a material to radiate energy
[00:00:28.010]with values between zero and one.
[00:00:30.810]A material with an emissivity value of one
[00:00:34.150]is called a perfect emitter or a perfect blackbody.
[00:00:38.460]Real materials have emissivity values
[00:00:40.310]between zero and one.
[00:00:42.330]Most uncoated metals have low emissivity,
[00:00:45.960]for example, aluminum and stainless steel 304,
[00:00:51.470]which are the materials used during the process
[00:00:54.040]of this research, have emissivity values of about 0.057
[00:00:58.405]and 0.16, respectively.
[00:01:02.340]Femtosecond laser surface processing or FLSP is a method
[00:01:07.520]that can be used to increase the emissivity of a surface
[00:01:10.450]without changing the bulk material properties.
[00:01:13.770]Previous work has shown that FLSP can be used
[00:01:17.140]to create near perfect omnidirectional emissivity,
[00:01:21.160]in values that when applied to aluminum can go
[00:01:24.579]as high as 0.95.
[00:01:28.270]By applying FLSP at an angle, microscale surface features
[00:01:32.760]can be created at the incident angle of the laser
[00:01:36.080]and result in surfaces with directional emissivity.
[00:01:40.384]The goal of this project is to gain understanding
[00:01:42.770]into the directional emissivity of FLSP surfaces
[00:01:46.406]and how to control the emission peak angle
[00:01:49.610]by characterizing the emission as a function of angle
[00:01:53.690]and by characterizing the micro
[00:01:55.570]and nanoscale surface features.
[00:02:01.080]The femtosecond laser surface processing experimental setup
[00:02:04.180]consists of the Coherent Astrella femtosecond laser
[00:02:07.850]with pulse width of 35 femtoseconds,
[00:02:10.250]center wavelength of eight hundred nanometers,
[00:02:13.230]repetition rate of one kilohertz
[00:02:14.770]and a pulse energy with a maximum value of six millijoule.
[00:02:19.000]The laser beam passes through a shutter in wavelength,
[00:02:22.290]polarizer through a set of mirrors until focused
[00:02:25.679]and redirect on a focusing optic to create a (indistinct)
[00:02:29.820]over the desired sample.
[00:02:31.939]For directional features, the CNC system
[00:02:35.717]with submicron resolution is used for 3D sample translation
[00:02:40.160]based on CAD files.
[00:02:41.690]This system allows laser surface processing to be applied
[00:02:44.890]at different angles.
[00:02:46.600]In this figure appears a typical raster scan path programmed
[00:02:51.470]to allow surface processing using the femtosecond laser
[00:02:54.460]surface processing over the desired area.
[00:03:00.621]Then we have a directional infrared emission
[00:03:03.330]data acquisition setup, because since the goal is
[00:03:06.950]to obtain directional emissivity results,
[00:03:09.490]an infrared camera is used to take temperature measurements
[00:03:12.870]from the detected angles from zero degrees
[00:03:15.360]to 85 degrees in increments of five.
[00:03:19.220]Then the data acquired with the thermal camera is used
[00:03:23.150]to calculate the directional emissivity values.
[00:03:26.520]In these figures is shown that a protractor is used
[00:03:30.430]to change the reference angle of the sample
[00:03:32.860]from measuring emissivity from zero to 360 degrees
[00:03:37.990]in increments of 15 or 45 degrees.
[00:03:42.620]Zero degrees is when the angle structure are tilted
[00:03:46.060]towards the detector that in this case
[00:03:49.470]is the infrared camera.
[00:03:53.810]During the process of these research,
[00:03:56.010]there are three parameters that are truly important
[00:03:59.230]for our samples, fluence value, pulse count
[00:04:02.390]and processing angle.
[00:04:04.890]By changing these parameters, we can obtain different micro
[00:04:08.030]and nanoscale surface features.
[00:04:10.240]As previously stated, for these research,
[00:04:13.160]two materials were used.
[00:04:15.600]The first one, stainless steel 304 with a fluence value
[00:04:20.608]of 3.25 joules per centimeter square, a pulse count
[00:04:25.450]of 5,755 and with a processing angle of 55 degrees.
[00:04:33.090]Scanning electron microscope images were taken
[00:04:36.330]at zero degrees, that is the top view of the features
[00:04:41.100]and 55 degrees that are the direct viewing to the features.
[00:04:45.550]Then using our 3D laser scanning confocal microscope,
[00:04:49.710]surface profiles were done at zero degrees
[00:04:52.970]to analyze the sample height.
[00:04:56.340]For our second material, aluminum,
[00:04:59.510]the samples were processed with different fluence values
[00:05:02.900]to compare the features and emissivity results.
[00:05:06.003]Both samples were processed with a pulse count of 506,
[00:05:10.950]and with a processing angle of 45 degrees.
[00:05:14.440]The difference is that the first sample was processed
[00:05:17.570]with a fluence value of 3.21 Joules per centimeter square
[00:05:22.430]and the second sample was processed at a fluence value
[00:05:25.498]of 5.21 Joules per centimeter square.
[00:05:29.730]And like in our first sample of stainless steel 304,
[00:05:35.340]scanning electron microscope images were taken
[00:05:39.240]to study the features of our samples
[00:05:42.870]and also 3D laser scanning confocal microscope
[00:05:46.670]surface profiles were done to study the height
[00:05:50.170]of our samples.
[00:05:53.360]After successfully characterizing
[00:05:55.230]the femtosecond laser surface processing
[00:05:57.470]multiscale features, the temperature was taken
[00:06:00.500]for each sample using the directional infrared emission
[00:06:03.950]data acquisition setup that was previously discussed.
[00:06:08.300]These values were then uploaded to a MATLAB program designed
[00:06:11.850]to solve the hemispherical emissivity equation.
[00:06:15.150]Graphs A, B and C are emissivity results from our samples.
[00:06:22.570]The only one with resultant directional emissivity
[00:06:28.040]was sample A.
[00:06:31.260]That is the stainless steel 304 sample.
[00:06:35.810]Then.
[00:06:38.610]After obtaining the directional emissivity results
[00:06:41.810]for our sample of stainless steel 304,
[00:06:44.890]a polar plot was created from angles
[00:06:48.780]through zero to 360.
[00:06:51.870]Know that this are the angle of reference to view
[00:06:56.020]and to visualize where was the peak directional emissivity
[00:07:00.960]that in this case is zero degrees.
[00:07:06.520]In conclusion, the directional emissivity was obtained
[00:07:09.960]for the stainless steel 304 sample that was processed
[00:07:13.450]at and angle of 55 degrees.
[00:07:16.150]Although increased hemispherical emissivity was obtained
[00:07:18.700]for laser processed aluminum, no directional emissivity
[00:07:22.580]was obtained for the laser parameters used.
[00:07:26.800]Fluence and pulse count can be used
[00:07:28.410]to control structure morphology and further adjustments
[00:07:31.720]of parameters may result in directional emissivity
[00:07:34.920]for aluminum.
[00:07:37.000]I want to take this opportunity to acknowledge
[00:07:39.320]that this material was supported
[00:07:40.750]by the National Science Foundation.
[00:07:42.340]And this research was performed
[00:07:44.230]in the Center of Electro-optics and Functionalized Surfaces
[00:07:47.530]in collaboration with the Nebraska Nanoscale Facility.
[00:07:50.630]I'm truly grateful for these program, for the opportunity
[00:07:53.410]to participate in this amazing experience.
[00:07:56.290]I want to thank Andrew Reicks for guiding me
[00:07:58.340]through the process data acquisition
[00:08:00.520]and my mentor, Dr. Craig Zuhlke for giving me full support
[00:08:03.780]in his research team during this research experience.
[00:08:06.800]Thank you.

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Directional Emissivity Using Femtosecond Laser Surface Processing

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