Name: automated delivery of microfabricated targets for intense laser irradiation experiments
Uploaded: 2021-01-28T13:00:00
Description: Watch this Scientific Journal Video about Automated Delivery of Microfabricated Targets for Intense Laser Irradiation Experiments at JoVE.com

This work has been supported by the Israel Science Foundation, grant No. 1135/15 and by the Zuckerman STEM Leadership Program, Israel, which are gratefully acknowledged. We also acknowledge the support of the Pazy Foundation, Israel grant #27707241, and NSF-BSF grant No. 01025495.&#160;The authors would like to kindly acknowledge Tel Aviv University Center for Nanoscience and Nanotechnolog

1. Target fabrication
NOTE: Figure 2 and Figure 3 illustrate the fabrication process of freestanding gold foils.
<ol>
	<li>Back Side
	<ol>
		<li>Use a 250 &#956;m thick, 100 mm diameter, high-stress silicon wafer in a &#60;100&#62; crystal formation, coated on both sides with silicon nitride.</li>
		<li>Clean the wafer using acetone&#160;followed by isopropanol and dry with nitrogen.&#160; Then spin coat a layer of HMDS&#160;to form...

<ol>
	<li>Snavely, R. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Intense+High-Energy+Proton+Beams+from+Petawatt-Laser+Irradiation+of+Solids.">Intense High-Energy Proton Beams from Petawatt-Laser Irradiation of Solids.</a> Physical Review Letters. 85, 4945 (2000).</li><li>Tosaki, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evaluation+of+laser-driven+ion+energies+for+fusion+fast-ignition+research.">Evaluation of laser-driven ion energies for fusion fast-ignition research.</a> Progress of Theoretical and Experimental Physics. 2017 (10), 103 (2017).</li><li>Borghesi, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Proton+imaging:+a+diagnostic+for+inertial+confinement+fusion/fast+ignitor+studies+Related+content+Inertial+confinement+fusion+and+fast+ignitor+studies.">Proton imaging: a diagnostic for inertial confinement fusion/fast ignitor studies Related content Inertial confinement fusion and fast ignitor studies.</a> Plasma Physics and Controlled Fusion. 43, 12 (2001).</li><li>Malka, V., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Practicability+of+proton+therapy+using+compact+laser+systems.">Practicability of proton therapy using compact laser systems.</a> Medical Physics. 31 (6), 1587-1592 (2004).</li><li>Roth, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Laser-Driven+Neutron+Source+Based+on+the+Relativistic+Transparency+of+Solids.">Laser-Driven Neutron Source Based on the Relativistic Transparency of Solids.</a> Physical Review Letters. 110, 044802 (2013).</li><li>Noaman-Ul-Haq, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Statistical+analysis+of+laser+driven+protons+using+a+high-repetition-rate+tape+drive+target+system.">Statistical analysis of laser driven protons using a high-repetition-rate tape drive target system.</a> Physical Review Accelerators and Beams. 20 (4), 41301 (2017).</li><li>Li, Z., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Protons+and+electrons+generated+from+a+5-&#956;m+thick+copper+tape+target+irradiated+by+s-,+circularly-,+and+p-polarized+55-fs+laser+pulses.">Protons and electrons generated from a 5-&#956;m thick copper tape target irradiated by s-, circularly-, and p-polarized 55-fs laser pulses.</a> Physics Letters, Section A: General, Atomic and Solid State Physics. 369 (5-6), 483-487 (2007).</li><li>Shaw, B. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-peak-power+surface+high-harmonic+generation+at+extreme+ultra-violet+wavelengths+from+a+tape.">High-peak-power surface high-harmonic generation at extreme ultra-violet wavelengths from a tape.</a> Journal of Applied Physics. 114 (4), 43106 (2013).</li><li>Fill, E., Bayerl, J., Tommasini, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+novel+tape+target+for+use+with+repetitively+pulsed+lasers.">A novel tape target for use with repetitively pulsed lasers.</a> Review of Scientific Instruments. 73 (5), 2190-2192 (2002).</li><li>Morrison, J. T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=MeV+proton+acceleration+at+kHz+repetition+rate+from+ultra-intense+laser+liquid+interaction.">MeV proton acceleration at kHz repetition rate from ultra-intense laser liquid interaction.</a> New Journal of Physics. 20 (2), 22001 (2018).</li><li>Margarone, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Proton+Acceleration+Driven+by+a+Nanosecond+Laser+from+a+Cryogenic+Thin+Solid-Hydrogen+Ribbon.">Proton Acceleration Driven by a Nanosecond Laser from a Cryogenic Thin Solid-Hydrogen Ribbon.</a> Physical Review X. 6, 041030 (2016).</li><li>Prencipe, I., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Targets+for+high+repetition+rate+laser+facilities:+needs,+challenges+and+perspectives.">Targets for high repetition rate laser facilities: needs, challenges and perspectives.</a> High Power Laser Science and Engineering. 5, 17 (2017).</li><li>Porat, E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Towards+direct-laser-production+of+relativistic+surface+harmonics.">Towards direct-laser-production of relativistic surface harmonics.</a> Proceedings Volume 11036, Relativistic Plasma Waves and Particle Beams as Coherent and Incoherent Radiation Sources III. , 110360 (2019).</li><li>Gershuni, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+gatling-gun+target+delivery+system+for+high-intensity+laser+irradiation+experiments.">A gatling-gun target delivery system for high-intensity laser irradiation experiments.</a> Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 934, 58-62 (2019).</li><li>Jung, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+of+a+high+resolution+and+high+dispersion+Thomson+parabola.">Development of a high resolution and high dispersion Thomson parabola.</a> Review of Scientific Instruments. 82 (1), 13306 (2011).</li><li>Cobble, J. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-resolution+Thomson+parabola+for+ion+analysis.">High-resolution Thomson parabola for ion analysis.</a> Review of Scientific Instruments. 82 (11), 113504 (2011).</li><li>Man&#269;i&#263;, A., Fuchs, J., Antici, P., Gaillard, S. A., Audebert, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Absolute+calibration+of+photostimulable+image+plate+detectors+used+as+high-energy+proton+detectors.">Absolute calibration of photostimulable image plate detectors used as high-energy proton detectors.</a> Review of Scientific Instruments. 79, 73301 (2008).</li><li>Mattox, D. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Processing. Handbook of Physical Vapor Deposition (PVD) Processing. , (2007).</li><li>Astrom, K. J., Murray, R. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Feedback Systems: An Introduction for Scientists and Engineers. , (2006).</li><li>Passoni, M., Bertagna, L., Zani, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Target+normal+sheath+acceleration:+Theory,+comparison+with+experiments+and+future+perspectives.">Target normal sheath acceleration: Theory, comparison with experiments and future perspectives.</a> New Journal of Physics. 12, 045012 (2010).</li><li>Roth, M., Schollmeier, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ion+Acceleration:+TNSA.">Ion Acceleration: TNSA.</a> Laser-Plasma Interactions and Applications. , 303-350 (2013).</li><li>Zaffino, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Efficient+proton+acceleration+from+a+3+TW+table-top+laser+interacting+with+submicrometric+mass-produced+solid+targets.">Efficient proton acceleration from a 3 TW table-top laser interacting with submicrometric mass-produced solid targets.</a> Journal of Physics Communications. 2 (4), 41001 (2018).</li><li>Harres, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+and+calibration+of+a+Thomson+parabola+with+microchannel+plate+for+the+detection+of+laser-accelerated+MeV+ions.">Development and calibration of a Thomson parabola with microchannel plate for the detection of laser-accelerated MeV ions.</a> Review of Scientific Instruments. 79 (9), 93306 (2008).</li><li>Robinson, A. P. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spectral+modification+of+laser-accelerated+proton+beams+by+self-generated+magnetic+fields+Related+content+New+Journal+of+Physics+Spectral+modification+of+laser-accelerated+proton+beams+by+self-generated+magnetic+fields.">Spectral modification of laser-accelerated proton beams by self-generated magnetic fields Related content New Journal of Physics Spectral modification of laser-accelerated proton beams by self-generated magnetic fields.</a> New Journal of Physics. 11 (15), 83018 (2009).</li><li>Treffert, F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Design+and+implementation+of+a+Thomson+parabola+for+fluence+dependent+energy-loss+measurements+at+the+Neutralized+Drift+Compression+experiment.">Design and implementation of a Thomson parabola for fluence dependent energy-loss measurements at the Neutralized Drift Compression experiment.</a> Review of Scientific Instruments. 89 (10), 103302 (2018).</li><li>Pappalardo, A., Cosentino, L., Finocchiaro, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+imaging+technique+for+detection+and+absolute+calibration+of+scintillation+light.">An imaging technique for detection and absolute calibration of scintillation light.</a> Review of Scientific Instruments. 81 (3), 33308 (2010).</li></ol>

With some variations, the target fabrication process described in this protocol is common (e.g., Zaffino et al.23). Here, one unique step that is critical to the operation of automatic positioning is the addition of nanometer-scale roughening in ring-shaped areas on the back of the wafer (step 1.2.3). The purpose of this step is to increase the diffused scattering of light incident on the wafer in those areas. The ranging sensor shines a low-power laser beam on the wafer, collects the scattered li...

An erratum was issued for:&#160;<a href="https://www.jove.com/t/61056">Automated Delivery of Microfabricated Targets for Intense Laser Irradiation Experiments</a>. The author list was updated.
The author list was updated from:
Yonatan Gershuni1,2, Michal Elkind1,2, Itamar Cohen1,2, Aviad Tsabary1,2, Deep Sarkar1,2, Ishay Pomerantz1,2 
1The School of Physics and Astronomy, Tel Aviv University, 
2Tel Aviv University Center for Light-Matter Interaction
to:
Yonatan Gershuni1,2, Michal Elkind1,2, Dolev Roitman1,2, Itamar Cohen1,2, Aviad Tsabary1,2, Deep Sarkar1,2, Ishay Pomerantz1,2 
1The School of Physics and Astronomy, Tel Aviv University, 
2Tel Aviv University Center for Light-Matter Interaction

An erratum was issued for:&#160;<a href="https://www.jove.com/t/61056">Automated Delivery of Microfabricated Targets for Intense Laser Irradiation Experiments</a>. The author list was updated.

Erratum: Automated Delivery of Microfabricated Targets for Intense Laser Irradiation Experiments

High-intensity laser irradiation of solid targets generates multiple forms of radiation. One of these is the emission of energetic ions with energies at the Mega electron-volt (MeV) level1. A compact source of MeV ions has potential for many applications, such as proton fast-ignition2, proton radiography3, ion radiotherapy4, and neutron generation5.
A major challenge in making laser-ion acceleration practical is the ability to position micrometer-scale targets accurately within the focus of the laser at a high rate. Few target delivery technologies were developed to answer this challenge. Most common are target systems based on micrometer-scale thick tapes. These targets are simple to replenish and may be easily positioned within the focus of the laser. Tape target has been made using VHS6, copper7, Mylar, and Kapton8 tapes. The tape drive system typically consists of two motorized spools for winding and unwinding and two vertical pins placed between them to keep the tape in position9. The accuracy in positioning the tape surface is typically less than the Rayleigh range of the focusing beam. Another type of replenishable laser target is liquid sheets10. These targets are delivered rapidly to the interaction region and introduce a very low amount of debris. This system comprises a high-pressure syringe pump continuously supplied with liquid from a reservoir. Recently, novel cryogenic hydrogen jets11 were established as means to deliver ultrathin, low-debris, replenishable targets.
The main drawback of all of these replenishable target systems is the limited choice of target materials and geometries, which are dictated by mechanical requirements such as strength, viscosity, and melting temperature.
Here, a system able to bring micromachined targets to the focus of a high intensity laser at a rate of 0.2 Hz is described. Micromachining offers a wide choice of target materials in versatile geometries12. The target positioning is performed by a closed-loop feedback between a commercial displacement sensor and a motorized manipulator.
The target delivery system was tested using a high-contrast, 20 TW laser system that delivers 25 fs-long laser pulses with 500 mJ on target. A review of the laser system&#8217;s architecture is given in Porat et al.13, and a technical description of the target system is given in Gershuni et al.14. This paper presents a detailed method for making and using this type of system and shows representative results of laser-ion acceleration from ultrathin gold foil targets.
The Thomson Parabola ion spectrometer (TPIS)15,16 shown in Figure 1 was used to record the energy spectra of the emitted ions. In a TPIS, accelerated ions pass through parallel electric and magnetic fields, which places them on parabolic trajectories in the focal plane. The parabolic curvature depends on the ion&#8217;s charge-to-mass ratio, and the location along the trajectory is set by the ion&#8217;s energy.
A BAS-TR imaging plate (IP)17 positioned at the focal plane of the TPIS records the impinging ions. The IP is attached to a mechanical feedthrough to allow translation to a fresh area before each shot.

<table>
	<tbody>
		<tr>
			<td>76.2 x 127mm EFL 90&#176; Protected Gold 100&#197; Off-Axis Parabolic Mirror</td>
			<td>Edmund optics</td>
			<td>35-535</td>
			<td></td>
		</tr>
		<tr>
			<td>MicroTrak 3 LTS 120-20</td>
			<td>MTI Instruments</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Ultrafast high power dielectric mirrors for 800 nm</td>
			<td>Thorlabs</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

automated delivery of microfabricated targets for intense laser irradiation experiments

Described is an experimental procedure that enables high-power laser irradiation of microfabricated targets. Targets are brought to the laser focus by a closed feedback loop that operates between the target manipulator and a ranging sensor. The target fabrication process is explained in detail. Representative results of MeV-level proton beams generated by irradiation of 600 nm thick gold foils at a rate of 0.2 Hz are given. The method is compared with other replenishable target systems and the prospects of increasing the shot rates to above 10 Hz are discussed.

This target delivery system was employed to accelerate ions from the back side of 600 nm thick gold foils. When irradiated with a normalized laser intensity of a0 = 5.6, these ions were accelerated by the target normal sheath acceleration (TNSA) mechanism21. In TNSA, the lower-intensity light that preceded the main laser pulse ionized the front surface of the target foil. The ponderomotive force exerted by the main laser pulse drove hot electrons through the bulk matter. A charge separa...

Watch this Scientific Journal Video about Automated Delivery of Microfabricated Targets for Intense Laser Irradiation Experiments at JoVE.com

Automated Delivery of Microfabricated Targets for Intense Laser Irradiation Experiments

A protocol is presented for automated irradiation of thin gold foils with high intensity laser pulses. The protocol includes a step-by-step description of the micromachining target fabrication process and a detailed guide for how targets are brought to the laser&#39;s focus at a rate of 0.2 Hz.

Described is an experimental procedure that enables high-power laser irradiation of microfabricated targets. Targets are brought to the laser focus by a ...

Intense laser radiation experiments of submicrometer scale targets are currently performed at slow shot rates. Our protocol solved this challenge by placing these targets quickly at the focus of the laser in an automated manner. Our target system enables the collection of data incorporating a large number of laser shots with target parameters changed in small increments, as well as applications that benefit from a high overall radiation dose.Visual demonstration of this protocol will show the subtleties of the wafer fabrication process and target alignment. Demonstrating target fabrication process are process engineer Nirit Porecki Shamay and Nofar Livni. To fabricate the backside, use a 250 micrometer thick 100 millimeter diameter high stress silicon wafer in a one-zero-zero crystal formation coated on both sides with silicon nitride.Clean the wafer with acetone and with isopropanol. Then spin coat the wafer with HMDS resists to form an adhesive layer. Spin coat the wafer with an AZ 1518 positive photoresist.Bake the wafer at 100 degrees Celsius for one minute. Photolithograph 1, 000 by 1, 000 micrometer square openings under vacuum, exposing the wafer in one four to seven-second cycle to a 400 nanometer UV lamp so that the wafer is exposed to an overall fluence of 40 joules per centimeter squared. Then use an AZ 726 developer to expose the silicon nitride and a bath of dehydrated water to stop the process.Use a reactive ion etcher to remove the silicon nitride in the location of the squares. Place the wafer in an NMP bath for 20 minutes to remove the residual resist and photoresist, producing a replica of the mask on the silicon nitride layer. Then wash it under fresh water and let it dry.Sink the wafer in a 30%90 degrees Celsius potassium hydroxide solution to etch the silicon through the square openings. To fabricate the front side, repeat the previously described procedure with a mask shaped as three concentric rings. Use the reactive ion etcher to remove the silicon nitride where the rings are located, followed by an NMP bath to remove resist and photoresist leftovers.Roughen the silicon rings by sinking the wafer in nitric acid and in a solution of 0.02 molar silver nitrate and four molar hydrogen fluoride. On the etched side of the wafer, use a physical vapor deposition machine to sputter a layer of a few hundred nanometers of gold on top of a 10 nanometer film of adhesive titanium, nickel, or chrome. Block the beam and bring the first target into view under a high magnification microscope.Point a triangulation ranging sensor to the roughened ring closest to the target and record its displacement reading. Leaving the microscope in place, move the wafer away to clear the beam path. Use the two folding mirrors and the off-axis parabolic mirror to align the beam in low power into the field of view of the microscope.Adjust these three mirrors to correct astigmatisms in the beam. The result should be a nearly diffraction limited focal spot. Block the laser beam and bring the target back to the focus of the microscope.Then validate its position using the microscope and the ranging sensors reading. Use software to implement a closed loop feedback between the focal axis manipulator of the target and the displacement sensor reading using the previously recorded displacement value as the setpoint. Once the closed loop positioning has reached a desired tolerance distance from the setpoint, irradiate the target with a single high-power laser pulse.Record data from particle diagnostics and repeat the process with the next target brought into focus by the software. This target delivery system was employed to accelerate ions from the backside of 600 nanometer thick gold foils. A time series of the target displacement along the focal axis is shown here.The values are relative to the focal position setpoint. The green dots indicate when the target displacement was within a tolerance value of one micrometer from the setpoint, which is when a laser shot was taken. Thomson parabola ion spectrometer traces were obtained from 14 consecutive irradiations of 600 nanometer thick gold foil targets.Energy spectrums were derived from these traces. The peak-to-peak stability of the maximum proton energy was within 10%Following this procedure, investigations of ion and electron acceleration from solid foils neuron generation can be performed in a systematic manner.

automated-delivery-microfabricated-targets-for-intense-laser

Research

JoVE Journal

Engineering

Characterization of Surface Modifications by White Light Interferometry: Applications in Ion Sputtering, Laser Ablation, and Tribology Experiments

In materials science and engineering it is often necessary to obtain quantitative measurements of surface topography with micrometer lateral resolution. From the measured surface, 3D topographic maps can be subsequently analyzed using a variety of software packages to extract the information that is needed.
In this article we describe how white light interferometry, and optical profilometry (OP) in general, combined with generic surface analysis software, can be used for materials science and engineering tasks. In this article, a number of applications of white light interferometry for investigation of surface modifications in mass spectrometry, and wear phenomena in tribology and lubrication are demonstrated. We characterize the products of the interaction of semiconductors and metals with energetic ions (sputtering), and laser irradiation (ablation), as well as ex situ measurements of wear of tribological test specimens.
Specifically, we will discuss:
<ol class="lroman">
	<li>Aspects of traditional ion sputtering-based mass spectrometry such as sputtering rates/yields measurements on Si and Cu and subsequent time-to-depth conversion.</li>
	<li>Results of quantitative characterization of the interaction of femtosecond laser irradiation with a semiconductor surface. These results are important for applications such as ablation mass spectrometry, where the quantities of evaporated material can be studied and controlled via pulse duration and energy per pulse. Thus, by determining the crater geometry one can define depth and lateral resolution versus experimental setup conditions.</li>
	<li>Measurements of surface roughness parameters in two dimensions, and quantitative measurements of the surface wear that occur as a result of friction and wear tests.</li>
</ol>
Some inherent drawbacks, possible artifacts, and uncertainty assessments of the white light interferometry approach will be discussed and explained.

White light microscope interferometry is an optical, noncontact and quick method for measuring the topography of surfaces. It is shown how the method can be applied toward mechanical wear analysis, where wear scars on tribological test samples are analyzed; and in materials science to determine ion beam sputtering or laser ablation volumes and depths.

In materials science and engineering it is often necessary to obtain quantitative measurements of surface topography with micrometer lateral resolution. ...

Fabrication of Nano-engineered Transparent Conducting Oxides by Pulsed Laser Deposition

Nanosecond Pulsed Laser Deposition (PLD) in the presence of a background gas allows the deposition of metal oxides with tunable morphology, structure, density and stoichiometry by a proper control of the plasma plume expansion dynamics. Such versatility can be exploited to produce nanostructured films from compact and dense to nanoporous characterized by a hierarchical assembly of nano-sized clusters. In particular we describe the detailed methodology to fabricate two types of Al-doped ZnO (AZO) films as transparent electrodes in photovoltaic devices: 1) at low O2 pressure, compact films with electrical conductivity and optical transparency close to the state of the art transparent conducting oxides (TCO) can be deposited at room temperature, to be compatible with thermally sensitive materials such as polymers used in organic photovoltaics (OPVs); 2) highly light scattering hierarchical structures resembling a forest of nano-trees are produced at higher pressures. Such structures show high Haze factor (&gt;80%) and may be exploited to enhance the light trapping capability. The method here described for AZO films can be applied to other metal oxides relevant for technological applications such as TiO2, Al2O3, WO3 and Ag4O4.

We describe the experimental method to deposit nanostructured oxide thin films by nanosecond Pulsed Laser Deposition (PLD) in the presence of a background gas. By using this method Al-doped ZnO (AZO) films, from compact to hierarchically structured as nano-tree forests, can be deposited.

Nanosecond Pulsed  Laser Deposition (PLD) in the presence of a background gas allows the deposition  of metal oxides with tunable morphology, structure, ...

Spatial Separation of Molecular Conformers and Clusters

Gas-phase molecular physics and physical chemistry experiments commonly use supersonic expansions through pulsed valves for the production of cold molecular beams. However, these beams often contain multiple conformers and clusters, even at low rotational temperatures. We present an experimental methodology that allows the spatial separation of these constituent parts of a molecular beam expansion. Using an electric deflector the beam is separated by its mass-to-dipole moment ratio, analogous to a bender or an electric sector mass spectrometer spatially dispersing charged molecules on the basis of their mass-to-charge ratio. This deflector exploits the Stark effect in an inhomogeneous electric field and allows the separation of individual species of polar neutral molecules and clusters. It furthermore allows the selection of the coldest part of a molecular beam, as low-energy rotational quantum states generally experience the largest deflection. Different structural isomers (conformers) of a species can be separated due to the different arrangement of functional groups, which leads to distinct dipole moments. These are exploited by the electrostatic deflector for the production of a conformationally pure sample from a molecular beam. Similarly, specific cluster stoichiometries can be selected, as the mass and dipole moment of a given cluster depends on the degree of solvation around the parent molecule. This allows experiments on specific cluster sizes and structures, enabling the systematic study of solvation of neutral molecules.

We present a technique that allows the spatial separation of different conformers or clusters present in a molecular beam. An electrostatic deflector is used to separate species by their mass-to-dipole moment ratio, leading to the production of gas-phase ensembles of a single conformer or cluster stoichiometry.

Gas-phase molecular physics and physical chemistry experiments commonly use supersonic expansions through pulsed valves for the production of cold ...

Convergent Polishing: A Simple, Rapid, Full Aperture Polishing Process of High Quality Optical Flats &amp; Spheres

Convergent Polishing is a novel polishing system and method for finishing flat and spherical glass optics in which a workpiece, independent of its initial shape (i.e., surface figure), will converge to final surface figure with excellent surface quality under a fixed, unchanging set of polishing parameters in a single polishing iteration. In contrast, conventional full aperture polishing methods require multiple, often long, iterative cycles involving polishing, metrology and process changes to achieve the desired surface figure. The Convergent Polishing process is based on the concept of workpiece-lap height mismatch resulting in pressure differential that decreases with removal and results in the workpiece converging to the shape of the lap. The successful implementation of the Convergent Polishing process is a result of the combination of a number of technologies to remove all sources of non-uniform spatial material removal (except for workpiece-lap mismatch) for surface figure convergence and to reduce the number of rogue particles in the system for low scratch densities and low roughness. The Convergent Polishing process has been demonstrated for the fabrication of both flats and spheres of various shapes, sizes, and aspect ratios on various glass materials. The practical impact is that high quality optical components can be fabricated more rapidly, more repeatedly, with less metrology, and with less labor, resulting in lower unit costs. In this study, the Convergent Polishing protocol is specifically described for fabricating 26.5 cm square fused silica flats from a fine ground surface to a polished ~&#955;/2 surface figure after polishing 4 hr per surface on a 81 cm diameter polisher.

Convergent Polishing: A Simple, Rapid, Full Aperture Polishing Process of High Quality Optical Flats & Spheres

A novel optical polishing process, called &#8220;Convergent Polishing&#8221;, which enables faster, lower cost polishing, is described. Unlike conventional polishing processes, Convergent Polishing allows a glass workpiece to be polished in a single iteration and with high surface quality to its final surface figure without requiring changes to polishing parameters.

Convergent Polishing is a novel polishing system and method for finishing flat and spherical glass optics in which a workpiece, independent of its initial ...

Laser-induced Forward Transfer for Flip-chip Packaging of Single Dies

Flip-chip (FC) packaging is a key technology for realizing high performance, ultra-miniaturized and high-density circuits in the micro-electronics industry. In this technique the chip and/or the substrate is bumped and the two are bonded via these conductive bumps. Many bumping techniques have been developed and intensively investigated since the introduction of the FC technology in 19601 such as stencil printing, stud bumping, evaporation and electroless/electroplating2. Despite the progress that these methods have made they all suffer from one or more than one drawbacks that need to be addressed such as cost, complex processing steps, high processing temperatures, manufacturing time and most importantly the lack of flexibility. In this paper, we demonstrate a simple and cost-effective laser-based bump forming technique known as Laser-induced Forward Transfer (LIFT)3. Using the LIFT technique a wide range of bump materials can be printed in a single-step with great flexibility, high speed and accuracy at RT. In addition, LIFT enables the bumping and bonding down to chip-scale, which is critical for fabricating ultra-miniature circuitry.

We demonstrate the use of the Laser-induced Forward Transfer (LIFT) technique for flip-chip assembly of optoelectronic components. This approach provides a simple, cost-effective, low-temperature, fast and flexible solution for fine-pitch bumping and bonding on chip-scale for achieving high-density circuits for optoelectronic applications.

Flip-chip (FC) packaging is a key technology for realizing high performance, ultra-miniaturized and high-density circuits in the micro-electronics ...

Selective Area Modification of Silicon Surface Wettability by Pulsed UV Laser Irradiation in Liquid Environment

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of biosensing devices. We report on a protocol of using KrF and ArF lasers irradiating Si (001) samples immersed in a liquid environment with low number of pulses and operating at moderately low pulse fluences to induce Si wettability modification. Wafers immersed for up to 4 hr in a 0.01% H2O2/H2O solution did not show measurable change in their initial contact angle (CA) ~75&#176;. However, the 500-pulse KrF and ArF lasers irradiation of such wafers in a microchamber filled with 0.01% H2O2/H2O solution at 250 and 65 mJ/cm2, respectively, has decreased the CA to near 15&#176;, indicating the formation of a superhydrophilic surface. The formation of OH-terminated Si (001), with no measurable change of the wafer&#8217;s surface morphology, has been confirmed by X-ray photoelectron spectroscopy and atomic force microscopy measurements. The selective area irradiated samples were then immersed in a biotin-conjugated fluorescein-stained nanospheres solution for 2 hr, resulting in a successful immobilization of the nanospheres in the non-irradiated area. This illustrates the potential of&#160;the method for selective area biofunctionalization and fabrication of advanced Si-based biosensing architectures. We also describe a similar protocol of irradiation of wafers immersed in methanol (CH3OH) using ArF laser operating at pulse fluence of 65 mJ/cm2 and in situ formation of a strongly hydrophobic surface of Si (001) with the CA of 103&#176;. The XPS results indicate ArF laser induced formation of Si&#8211;(OCH3)x compounds responsible for the observed hydrophobicity. However, no such compounds were found by XPS on the Si surface irradiated by KrF laser in methanol, demonstrating the inability of the KrF laser to photodissociate methanol and create -OCH3 radicals.

We report on a process of in situ alteration of HF treated Si (001) surface into a hydrophilic or hydrophobic state by irradiating samples in microfluidic chambers filled with&#160;H2O2/H2O solution (0.01%-0.5%) or methanol solutions using pulsed UV laser of a relative low pulse fluence.

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of ...

Compact Lens-less Digital Holographic Microscope for MEMS Inspection and Characterization

A micro-electro-mechanical-system (MEMS) is a widely used component in many industries, including energy, biotechnology, medical, communications, and automotive. However, effective inspection and characterization metrology systems are needed to ensure the functional reliability of MEMS. This study presents a system based on digital holography as a tool for MEMS metrology. Digital holography has gained increasing attention in the past 20 years. With the fast development and decreasing cost of sensor arrays, resolution of such systems has increased broadening potential applications. Thus, it has attracted attention from both research and industry sides as a potential reliable tool for industrial metrology. Indeed, by recording the interference pattern between an object beam (which contains sample height information) and a reference beam on a CCD camera, one can retrieve the quantitative phase information of an object. However, most of digital holographic systems are bulky and thus not easy to implement on industry production lines. The novelty of the system presented is that it is lens-less and thus very compact. In this study, it is shown that the Compact Digital Holographic Microscope (CDHM) can be used to evaluate several characteristics typically consider as criteria in MEMS inspections. The surface profiles of MEMS in both static and dynamic conditions are presented. Comparison with AFM is investigated to validate the accuracy of the CDHM.

We present a compact reflection digital holographic system (CDHM) for inspection and characterization of MEMS devices. A lens-less design using a diverging input wave providing natural geometrical magnification is demonstrated. Both static and dynamic studies are presented.

A micro-electro-mechanical-system (MEMS) is a widely used component in many industries, including energy, biotechnology, medical, communications, and ...

Automation of Mode Locking in a Nonlinear Polarization Rotation Fiber Laser through Output Polarization Measurements

When a laser is mode-locked, it emits a train of ultra-short pulses at a repetition rate determined by the laser cavity length. This article outlines a new and inexpensive procedure to force mode locking in a pre-adjusted nonlinear polarization rotation fiber laser. This procedure is based on the detection of a sudden change in the output polarization state when mode locking occurs. This change is used to command the alignment of the intra-cavity polarization controller in order to find mode-locking conditions. More specifically, the value of the first Stokes parameter varies when the angle of the polarization controller is swept and, moreover, it undergoes an abrupt variation when the laser enters the mode-locked state. Monitoring this abrupt variation provides a practical easy-to-detect signal that can be used to command the alignment of the polarization controller and drive the laser towards mode locking. This monitoring is achieved by feeding a small portion of the signal to a polarization analyzer measuring the first Stokes parameter. A sudden change in the read out of this parameter from the analyzer will occur when the laser enters the mode-locked state. At this moment, the required angle of the polarization controller is kept fixed. The alignment is completed. This procedure provides an alternate way to existing automating procedures that use equipment such as an optical spectrum analyzer, an RF spectrum analyzer, a photodiode connected to an electronic pulse-counter or a nonlinear detecting scheme based on two-photon absorption or second harmonic generation. It is suitable for lasers mode locked by nonlinear polarization rotation. It is relatively easy to implement, it requires inexpensive means, especially at a wavelength of 1550 nm, and it lowers the production and operation costs incurred in comparison to the above-mentioned techniques.

A protocol to detect and automate mode locking in a pre-adjusted nonlinear polarization rotation fiber laser is presented. The detection of a sudden change in the output polarization state when mode locking occurs is used to command the alignment of an intra-cavity polarization controller in order to find mode-locking conditions.

When a laser is mode-locked, it emits a train of ultra-short pulses at a repetition rate determined by the laser cavity length. This article outlines a ...

Fabrication of 1-D Photonic Crystal Cavity on a Nanofiber Using Femtosecond Laser-induced Ablation

We present a protocol for fabricating 1-D Photonic Crystal (PhC) cavities on subwavelength-diameter tapered optical fibers, optical nanofibers, using femtosecond laser-induced ablation. We show that thousands of periodic nano-craters are fabricated on an optical nanofiber by irradiating with just a single femtosecond laser pulse. For a typical sample, periodic nano-craters with a period of 350 nm and with diameter gradually varying from 50 - 250 nm over a length of 1 mm are fabricated on a nanofiber with diameter around 450 - 550 nm. A key aspect of such a nanofabrication is that the nanofiber itself acts as a cylindrical lens and focuses the femtosecond laser beam on its shadow surface. Moreover, the single-shot fabrication makes it immune to mechanical instabilities and other fabrication imperfections. Such periodic nano-craters on nanofiber, act as a 1-D PhC and enable strong and broadband reflection while maintaining the high transmission out of the stopband. We also present a method to control the profile of the nano-crater array to fabricate apodized and defect-induced PhC cavities on the nanofiber. The strong confinement of the field, both transverse and longitudinal, in the nanofiber-based PhC cavities and the efficient integration to the fiber networks, may open new possibilities for nanophotonic applications and quantum information science.

We present a protocol for fabricating 1-D photonic crystal cavities on subwavelength diameter silica fibers (optical nanofibers) using femtosecond laser-induced ablation.

We present a protocol for fabricating 1-D Photonic Crystal (PhC) cavities on subwavelength-diameter tapered optical fibers, optical nanofibers, using ...

Fabrication of Polymer Microspheres for Optical Resonator and Laser Applications

This paper describes three methods of preparing fluorescent microspheres comprising &#960;-conjugated or non-conjugated polymers: vapor diffusion, interface precipitation, and mini-emulsion. In all methods, well-defined, micrometer-sized spheres are obtained from a self-assembling process in solution. The vapor diffusion method can result in spheres with the highest sphericity and surface smoothness, yet the types of the polymers able to form these spheres are limited. On the other hand, in the mini-emulsion method, microspheres can be made from various types of polymers, even from highly crystalline polymers with coplanar, &#960;-conjugated backbones. The photoluminescent (PL) properties from single isolated microspheres are unusual: the PL is confined inside the spheres, propagates at the circumference of the spheres via the total internal reflection at the polymer/air interface, and self-interferes to show sharp and periodic resonant PL lines. These resonating modes are so-called "whispering gallery modes" (WGMs). This work demonstrates how to measure WGM PL from single isolated spheres using the micro-photoluminescence (&#181;-PL) technique. In this technique, a focused laser beam irradiates a single microsphere, and the luminescence is detected by a spectrometer. A micromanipulation technique is then used to connect the microspheres one by one and to demonstrate the intersphere PL propagation and color conversion from coupled microspheres upon excitation at the perimeter of one sphere and detection of PL from the other microsphere. These techniques, &#181;-PL and micromanipulation, are useful for experiments on micro-optic application using polymer materials.

Protocols for the synthesis of microspheres from polymers, the manipulation of microspheres, and micro-photoluminescence measurements are presented.