Pinky-powered Photons is an activity created by the Michigan Light Project during the International Year of Light to encourage creativity in learning about light. It is a low-cost project. Participants make and take home a colorful LED light powered entirely by their fingers. Younger visitors "package" the electrical element into their own creation while older visitors solder the electrical parts together and then create their own design. This paper will detail the learning objectives and outcomes of this project as well as how to implement it in an outreach event or classroom.
Outdoor holography is an activity created by the Michigan Light Project during the International Year of Light. Traditional holography is done in dark and quiet rooms. Using a kit from LitiHolo.com, we designed a way to make simple holograms outside in a noisy festival environment.
The 2015 International Year of Light created a wonderful opportunity to bring light and optics events and activities to people of all ages and occupations in Michigan. A large spectrum of events took place; from events held in schools, colleges, and universities targeting various groups of students, to events associated with festivals attended by large crowds. The latter included the Ann Arbor Summer Festival held in June and the Flint Back-to-the-Bricks Festival in August. All events included interactive activities where participants learned hands-on about optics and photonics phenomena and applications. Original demonstrations and kits were developed by the Ann Arbor OSA Local Section and the Optics Society at the University of Michigan, the joint OSA/SPIE student chapter, for use during the events. The activities were funded through the student chapter’s SPIE grant for IYL outreach events and corporate sponsorships. Under the name Michigan Light Project, these groups along with local technology enthusiasts and science clubs delivered several events across Michigan. Other events took place throughout the year in Mid-Michigan through the efforts of faculty and students in the Photonics and Laser Technology program at Baker College of Flint. The outreach events targeted students in K-12. Teachers, counselors, and parents also learned about the importance of optics and photonics in society. The activities developed will continue this year and in the future. The paper will provide details on the completed events and activities along with tips for implementing similar activities and outreach partnerships in other areas.
Relativistic electron beams have applications spanning materials science, medicine, and home- land security. Recent advances in short pulse laser technology have enabled the production of very high focused intensities at kHz rep rates. Consequently this has led to the generation of high ux sources of relativistic electrons- which is a necessary characteristic of these laser plasma sources for any potential application. In our experiments, through the generation of a plasma with the lambda cubed laser system at the University of Michigan (a 5 × 1018W=cm2, 500 Hz, Ti:Sapphire laser), we have measured electrons ejected from the surface of fused silica nd Cu targets having energies in excess of an MeV. The spectrum of these electrons was measured with respect to incident laser angle, prepulse timing, and focusing conditions. While taken at a high repetition rate, the pulse energy of the lambda cubed system was consistently on the order of 10 mJ. In order to predict scaling of the electron energy with laser pulse energy, simulations are underway which compare the spectrum generated with the lambda cubed system to the predicted spectrum generated on the petawatt scale HERCULES laser system at the University of Michigan.
An ultra-relativistic electron beam passing through a thick, high-Z solid target triggers an electromagnetic cascade, whereby a large number of high energy photons and electron-positron pairs are produced. By exploiting this physical process, we present here the first experimental evidence of the generation of ultra-short, highly collimated and ultra-relativistic positron beams following the interaction of a laser-wakefield accelerated electron beam with high-Z solid targets. Clear evidence has also been obtained of the generation of GeV electron-positron jets with variable composition depending on the solid target material and thickness. The percentage of positrons in the overall leptonic beam has been observed to vary from a few per cent up to almost fifty per cent, implying a quasi-neutral electron-positron beam. We anticipate that these beams will be of direct relevance to the laboratory study of astrophysical leptonic jets and their interaction with the interstellar medium.
We report on an experimental demonstration of laser wake field electron acceleration using few-milijoule laser pulses tightly focused on a 100 μm scale gas target. Using a comparatively low energy pulse has the benefit of a more compact system with a high repetition rate (typically kHz), which can prove useful for both practical applications and better statistical studies of laser plasma interactions. A proof-of-principle experiment was conducted to demonstrate the applicability of such electron sources from laser plasma wake field accelerator for ultrafast electron diffraction.
Electron-positron pair creation is among the QED-effects known to occur in a strong laser pulse interaction
with a counter-propagating electron beam. In this regime multiple pairs may be generated from a single beam
electron, some of the newborn particles being capable of further pair production. Radiation back-reaction
prevents avalanche development and limits pair creation. The system of integro-differential kinetic equations for
electrons, positrons and γ-photons is solved numerically.
Past works have used high-order harmonics in gas targets to demonstrate attosecond pulse generation. However, recent theoretical simulations have shown that solid-surface harmonics can also be used to produce attosecond pulses. Solid-surface harmonics are generated when a high-intensity femtosecond laser pulse irradiates a solid target surface at an oblique incidence angle. The conversion efficiency of this phenomenon increases rapidly with increasing pump laser intensity, and there is also no presently known upper limit in the pump intensity that can be used. Accordingly, this method possesses the potential for high-energy attosecond pulse generation. The main aim of this paper is to experimentally clarify the optimal conditions for highly efficient solid-surface harmonic generation. We demonstrate up to the 16th harmonic (49.1 nm wavelength) of a Ti:sapphire laser using modest pump intensities of 4×1016 W cm-2 irradiating a silicon wafer target. Investigations with low-order harmonics have revealed a large dependence of harmonic conversion efficiency on the target material. Furthermore, a drastic increase in the harmonic intensity has been observed by repetitively irradiating a metallic-coated target.
We investigated ultrafast laser-based x-ray (ULX) source as an attractive alternative to a microfocal x-ray tube used in micro-CT systems. The laser pulse duration was in the 30 fs-200 fs range, the repetition rate in the 10 Hz - 1 kHz range. A number of solid targets including Ge, Mo, Rh, Ag, Sn, Ba, La, Nd with matching filters was used. We optimized conditions for x-rays generation and measured: x-ray spectra, conversion efficiency (from laser light to x-rays), x-ray fluence, effective x-ray focal spot size and spatial resolution, contrast resolution and radiation dose. Good quality projection images of small animals in single-and dual-energy mode were obtained. ULX generates narrow x-ray spectra that consist mainly of characteristic lines that can be easily tailored (by changing laser beam target) to the imaging task, (e.g. to maximize contrast while minimizing radiation dose). X-ray fluence can exceed fluence produced by conventional microfocal tube with 10 μm focal-spot hence allowing for faster scans with very high spatial resolution. Changing the laser target, and thus matching the characteristic emission lines with the investigated animal's thickness and composition, can be done quickly and easily. Using narrow emission lines for imaging, instead of broad bremsstrahlung, offers superior dose utilization and limits beam-hardening effects. Employing two narrow emission lines-above and below the absorption edge of a contrast agent-in quick succession allows dual-energy-subtraction micro-CT for imaging with a contrast medium. Dual-energy-subtraction is not practical with a microfocal tube. Compact, robust, ultrafast lasers are commercially available, and their characteristics are rapidly improving. We plan to construct a prototype in vivo ultrafast laser-based micro-CT system.
Hard x-ray (8-100 keV) spectrum emission from plasma produced by femtosecond laser solid target interactions and Kα x-ray conversion efficiency have been studied as a function of laser intensity (1017 W/cm2 ~ 1019 W/cm2), pulse duration (70 fs ~ 400 fs), laser pulse fluence and laser wavelength (800 nm and 400 nm). The Ag Kα x-ray conversion efficiency produced by a laser pulse at 800 nm with an intensity I = 4x1018 W/cm2 can reach 2x10-5. We discuss the behavior of Kα conversion efficiency scaling laws as a function of the laser parameters. We found that the Kα x-ray conversion efficiency is more dependent on laser fluence than on pulse duration or laser pulse intensity. The conversion efficiency exhibits a similar value at I ~ 1x1018 W/cm2 when we work with a high contrast laser pulse at 400 nm or with a low contrast laser pulse at 800 nm, but in the first case it presents a higher scaling law. Consequently, the use of 400 nm laser pulses could be an effective method to optimize the Kα x-ray emission via vacuum heating mechanisms.
Generation of relativistic electrons from the interaction of a laser pulse with a high density plasma foil, accompanied by an underdense preplasma in front of it, has been studied with 2D particle-in-cell (PIC) simulations for pulse duration comparable to a single-cycle and for single-wavelength spot size. The primary mechanism responsible for electron acceleration is identified. Simulations show that the energy of the accelerated electrons has a maximum versus the pulse-duration for relativistic laser intensities. The most effective electron acceleration takes place when the preplasma scale length is comparable to the pulse-duration. Electron distribution functions have been found from PIC simulations. Their tails are well approximated by Maxwellian distributions with a hot temperature in the MeV range.
Characteristic Kα emissions from Mo, Ag and La targets irradiated by 60 fs, 600 mJ, 10 Hz Ti: Sapphire laser pulse at 1017 W/cm2 - 1019 W/cm2 can be potentially used in x-ray mammography. We have investigated x-ray spectra created by this novel x-ray source in this context. All the obtained spectra exhibited a dominating narrow emission lines with only a small portion of x-ray emission in Bremsstrahlung. Such spectra might be very usful in mammography and might improve contrast and dose utilizaion, as compared to a conventional mammographic x-ray tube. The effective focal spot size was of the order of 50 μm, i.e. significantly smaller than in conventional mammography. In contradiction to conventional mammography the effective x-ray focal spot size and the effective dose remained constant across the field of view. Kα conversion efficiency, from laser light to x-rays, was optimized and values as high as 2 x 10-5 have been obtained.
Spatial separation of isotopes in ultrafast laser ablation plumes is observed for a variety of elements in the periodic table. Observations are made with a charge-state discriminating mass analyzer as a function of angle relative to the center of the ablation plume. Data is presented for femtosecond and picosecond laser pulses showing enrichments by factors of 2 to 20 depending on element, charge state, and laser pulse duration. Thin films are deposited from the plasma plumes, as a function of distance from the ablation source, and used to record the spatial distribution of isotopes. This information is utilized to construct a model for the isotopic separation process and to infer characteristics of the electromagnetic fields in the ablation plasmas.
Pulsed-laser deposition has proved to be a promising method for producing complex inorganic thin films. One of its major advantages, relative to other methods, is the capability of controlling many process parameters, such as laser pulse width, energy, and wavelength along with background reactive gas pressure and substrate bias. Adjusting these parameters provides a pre-tuning of the laser plasma thereby allowing for optimum process conditions in a particular thin film deposition. Understanding and fully characterizing such highly-dynamic and rapidly-streaming plasmas requires multiple techniques for monitoring the plasmas at different stages. By combining different diagnostic methods, it is possible to analyze the broad time window over which these ablation plasmas develop and to understand the related processes that occur. We present in this work new results involving correlation of time-resolved Langmuir probe data, optical emission spectroscopy, and electrostatic energy analysis to characterize the laser-induced plasmas generated from targets of titanium, tin-dioxide and aluminum. Two laser sources, an 80 fs Ti:Sapphire laser (780 nm) and a 6 ns Nd:YAG laser (1.06 micrometer), were used in this work. Examples of very high quality, epitaxial tin-dioxide films grown on sapphire by femtosecond-laser MBE are presented. These films are evaluated by high-resolution, cross-sectional TEM and x-ray diffraction. Film quality is considered in relation to the ablation plasma parameters, wherein femtosecond and nanosecond plasmas are compared.
We present the theoretical limits for generation of high focused intensity laser. The important role of high- saturation-fluence materials is established and the use of regenerative chirped pulsed amplification to achieve high energy extraction from such materials is discussed. A regenerative chirped pulse amplification model and related experiments support the view that the surface damage threshold does not limit the range of useful laser materials to those with saturation fluence below the surface damage threshold. In addition the importance of phase measurement and control in providing well-defined conditions for experiments are noted.
A high energy flashlamp pumped Ti:sapphire laser has been developed for the pumping source of Yb:glass chirped pulse amplification. The free running oscillator generates 12 Joule/pulse at 793 nm at 1 Hz repetition. The output energy of 6 Joule/pulse at 920 nm has been obtained.
High-speed electronics was introduced into the subpicosecond regime by the applicaiton of short-pulse lasers to semiconductor systems. Photoconductive sampling, electrooptic sampling, as well as other ultrafast phenomena, have provided tools for the investigation of the behavior of solid-state materials on the ultrafast time-scale. Low-temperature-grown GaAs (LT GaAs) holds unique advantages for high-speed optoelectronics when employed with metal-semiconductor-metal photodetector (MSM) technology. To properly utilize this material we must consider its properties and the nature of the circuits and devices in which it will be used. The use of the MSM on LT GaAs as a small-signal detector and as a high-speed sampling gate has been demonstrated. Work is under way to develop materials with picosecond response and high resistivity, but with longer-wavelength sensitivity.
We describe our work on the amplification of short pulses in tunable solid state materials; specifically alexandrite and Ti:sapphire.
Our goal is to amplify femtosecond range pulses to the joule level in a table top size laser. We will describe our results which show
that such a laser is now feasible.