1.

INTRODUCTION

As seen in Fig. 1, the Laser Propagation Demonstration (LPD) is setup to interactively display the optical effects associated with coherent light propagation through atmospheric turbulence^1,2. For this purpose, a green laser diode is set on the front end of a meter long optical rail. The laser beam from the green laser diode is then sent through various optical components placed along the optical rail to better highlight the optical effects that manifest from a rotating turbulence phase screen. After, the laser light meets a beam sampler set at a 45 degree angle. Approximately 95% of the laser light is transmitted through the beam sampler and is then projected onto a screen set on the back end of the optical rail. The reflected light from the beam sampler is then imaged onto a camera located on the back end of a separate optical rail also oriented at a 45 degree angle. This allows for the laser light to be seen on a laptop screen in addition to a projector when available.

Figure 1.

The LPD in action during a recent outreach event at AFIT (winter 2014). Here, an AFIT SPIE Student Chapter member demonstrates the optical effects associated with coherent light propagation through atmospheric turbulence. Over 100 students participated in this two-day outreach event, grades 6-8.

Use of the optical rails allows for easy transportation and table-top setup of the LPD. It also provides added versatility in the fact that the demonstration builds on itself in a fun hands-on way. As such, the LPD is appropriate for both large and small crowds. With smaller crowds, a one-on-one approach is used. The interested student is able to adjust the various optical components themselves placed along the optical rail with the help of an Air Force Institute of Technology (AFIT) SPIE Student Chapter member. With a larger crowd, the various concepts are taught by an AFIT SPIE Student Chapter member. In either setting, accompanying handouts and posters boards allow for the audience to follow along with the explanations and ask questions to stimulate involvement at all levels. The LPD has the ability to appeal to a diverse crowd of inquisitive learners.

Section two of this paper provides an overview of the LPD’s development. Here, the reader gets to visually see the LPD in action at various outreach events. Section three provides an overview of LPD’s design and makes reference to a parts/price list located in the Appendix of this paper. Using this parts/price list, the interested reader can build their very own LPD! Section four then provides a conclusion for this paper with a roadmap for future upgrades that are currently in the mix.

2.

OVERVIEW OF THE LPD’S DEVELOPMENT

The LPD initially came into existence thanks to a LaserFest grant awarded by SPIE in 2010 for approximately $650. Ongoing research at AFIT in directed energy^3,4,5 and space situational awareness^6,7,8 served as the inspiration for the LPD’s design. As shown in Fig. 2, associated with this ongoing research is the idea that coherent light from a laser has to propagate through the atmosphere, which leads to multiple engineering constraints when dealing with military applications. With this in mind, the AFIT SPIE Student Chapter wanted to develop a way to demonstrate the optical effects of atmospheric turbulence on coherent light propagation^1,2. Attendance at the 2010 Adaptive Optics Summer School (put on by the Center for Adaptive Optics at the University of California Santa Cruz) presented a clever way to simulate atmospheric turbulence in the laboratory⁹. Using this idea, the LPD’s initial design was made part of a LaserFest lecture series held by AFIT (fall 2010), as seen in Fig. 3. Two distinguished researchers, Dr. Verdeyen¹⁰ and Dr. Hogge¹¹, served as guest speakers. As required by the LaserFest grant, the SPIE Student Chapter developed handouts and poster boards to accompany the LPD (also seen in Fig. 3). Figures 4 and 5 give a more detailed view of the developed handouts, which are still in use to this day. Note that these handouts help to explain the underlying physics, experimental design, and military applications associated with the LPD.

Figure 2.

Description of ongoing research being performed at AFIT, which inspired the LPD’s design. Specifically a.) describes a nominal directed energy engagement scenario where a high energy laser (HEL) engages a distant target, while b.) describes a nominal space situational awareness scenario where a laser illuminates a distant object. Associated with both of these descriptions is the idea that coherent light from a laser has to propagate through the atmosphere.

Figure 3.

The initial design for the LPD. A red laser diode was set at the front end of a meter long optical rail. The laser beam from the red laser diode was then sent through a pinhole and collimating lens. A rotating turbulence phase screen was also added to the optical train to show the effects of a simulated atmosphere. a.) shows the LPD with the accompanying posters, whereas b.) shows the LPD with the accompanying handouts. See Fig. 3). Figs. 4 and 5 for more detail.

Figure 4.

The handout associated with the LPD. This side of the handout gives theoretical and experimental explanations.

Figure 5.

The handout associated with the LPD. This side of the handout introduces military applications.

In an effort to make the LPD more interactive and portable, it went through several design upgrades. As seen in Figs. 6 and 7, these design upgrades made an appearance at a multitude of outreach events around the Dayton, Ohio area. These outreach events include: Rosa Parks Middle School, the Boonshoft Museum, the AFIT campus, the 2013 TechFest at Sinclair Community College, the 2013 Junior Science and Humanities Symposium, and St. Xavier High School (to name a few). The LPD was also displayed at the 2011, 2012, and 2013 SPIE Optics Outreach Olympics/Games, as seen in Fig. 8. In 2011 and 2012 the LPD received third place bronze medals and in 2013 an honorable mention.

Figure 6.

Various outreach events involving the LPD (2011-2013). a.) and b.) show the LPD at Rosa Parks Middle School with approximately 25 student participants, grades 6-8; c.) shows the LPD at the Boonshoft Museum with over 100 student participants, grades K-12; d.) shows the LPD at AFIT with a pack of Cub Scout visitors, grades 4-5; and e.) and f.) show the LPD at TechFest with over 2000 student participants, grades K-12.

Figure 7.

Various outreach events involving the LPD (2013-2014). a.) and b.) show the LPD at the Junior Science and Humanities Symposium with over 500 student participants, grades 9-12; c.) and d.) show the LPD at Rosa Parks Middle School with approximately 25 student participants, grades 6-8; and e.) and f.) show the LPD at St. Xavier High School with approximately 25 student participants, grades 11-12.

Figure 8.

Participation in the 2011, 2012, and 2013 SPIE Optics Outreach Olympics/Games. a.) and b.) shows the 2011 LPD display, whereas c.) and d.) shows the 2012 LPD display—both displays won third place bronze metals. e.) and f.) shows the 2013 LPD display, which received a fourth place honorable mention.

The reader should also note that the AFIT SPIE Student Chapter currently owns all of the LPD’s parts outright thanks to continued support from a 2012 SPIE Education Outreach Grant for approximately $2500. We greatly appreciate SPIE’s support!

3.

OVERVIEW OF THE LPD’S DESIGN

The LPD is a tried and true optics and photonics demonstration, and the AFIT SPIE Student Chapter hopes to share what we have learned through its development. The Appendix contains a parts/price list for all of the LPD’s components. Assuming, that you have access to an optics lab with the various tools required for assembly, you can build a similar upgraded demonstration for around $3300; however, a basic design can also be constructed for less than $2000! Figure 9 below shows a description for both designs, which primarily use optical components from Thorlabs. The only custom parts included in the LPD’s design are the turbulence phase screen and the amplitude masks, as shown in Fig. 10.

Figure 9.

Description of the LPD. A parts list for both the upgraded and basic designs is given in the Appendix

Figure 10.

A detailed look at a.) the turbulence phase screen and b.) the amplitude masks used with the LPD.

Both the turbulence phase screen and the amplitude masks are easy to make in practice. For example, to make the turbulence phase screen, the interested reader should use a clear cd that comes on the top or bottom of a stack of blank cds. Proceed to lightly coat it with hair spray or clear acrylic spray paint^9,12. This causes changes in the index of refraction which distorts the phase of the incident laser light. Upon propagation, this gives rise to constructive and destructive interference, also known as scintillation, and distortion upon imaging^1,2. In addition, to make the amplitude masks, simply print the examples provided in Fig. 10 on clear transparencies or design your own using Microsoft PowerPoint. It’s that easy!

4.

CONCLUSION

This paper reviews the success of the LPD—AFIT’s legacy outreach effort in optics and photonics. It is our hope that the interested reader can improve our design and share it with the STEM-based outreach community. The SPIE Student Chapter at AFIT plans to continually upgrade the LPD as well. In the near future, we plan to finish building robust carrying cases so that transportation of the LPD is even easier! With that said, if you have questions, please do not hesitate to ask—you may contact the first author via the info given above.

The views expressed in this paper are those of the authors and do not reflect the official policy or position of the U.S. Air Force, Department of Defense, or the U.S. government.