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Sep 08

By Lynn Savage

While I am sure that some people find that attending conferences can be a bit of a chore – something to get done as soon as possible before heading back to “real work” – that has never been true for me. And I don’t know you very well, but I’m guessing conferences aren’t a burden to you either, given that you’re here, reading about one that won’t arrive for months.

Of course, the one that we’re here to discuss is CLEO, one of the liveliest of all industry shows (and not just in the photonics industry). I’ll admit that I have a soft spot for CLEO; it was my first photonics conference ever (Baltimore, 2005, if you’re keeping score). The constant buzz of activity in the venue included a whirl of people and technologies that insisted on constant engagement. Academic researchers making last-minute adjustments to their presentations, post-docs

Technologies being showcased at CLEO

Technologies being showcased at CLEO

seeking their assigned spot in the poster area, salespeople seeking places to converse with clients, marketing reps setting up trade show booths, CLEO management show-runners scrambling to make sure everything from registration to AV tech to the coatrooms were operating smoothly — everyone with their individual missions and goals, gathered together to make sparks fly. It was a heady mix for any first timer, but I was thrilled to be there and dive in with my own, journalistic, goals.

Although my current avocation is science journalism, it has come via a path that began when I first trained to become a mechanical drafter. Although this never became a career, I really enjoyed the design process and the meticulous way one must consider form and function when laying designs out on paper. One of my favorite things about being a student of the drafter’s craft, though, was perusing catalogs filled with mechanical devices, from simple screws and bolts to advanced tools and heavy machinery. These catalogs informed me of a larger world of invention and craftsmanship that I wanted to tap into.

So, as exciting as it is to hear about advances in basic science and perhaps-someday-feasible technologies coming out of academic, government, and commercial laboratories around world, seeing the best of the lot make their way into the “real” world of applications is, frankly, often thrilling. It’s like watching your favorite minor league ballplayer break into the big leagues, finally earning a chance to swing the bat against the Clayton Kershaws of the world.

To support the idea that exciting developments are happening on the path from lab to market, CLEO is looking for even more input in 2015 from optical engineers, the people who take promising research results and translate them into amazing products.

For CLEO: 2015, the CLEO team is looking for presentations that will delight and inspire future developments, making sure that there is a steady spotlight on the pipeline of innovation in the optics and photonics world. Specifically, the organization hopes to see submissions in the following areas:

Biomedical applications

  • Biomedical spectroscopy, microscopy, and imaging
  • Neurophotonics and brain activity monitoring
  • Optogenetics and optical control of cells
  • Light sources and devices for biomedical imaging
  • Clinical technologies and systems

Industrial applications

  • New laser sources for industrial use
  • Micro/nanoprocessing and manufacturing
  • Sensing and process control
  • Ultrafast lasers

Photonic instrumentation and techniques for metrology and industrial processes 

  • Chemical sensing
  • Security applications
  • Process monitoring
  • Metrology

Lasers and photonic applications to energy and environment

  • New energy sources
  • Solar energy systems
  • Photonic instrumentation for energy and environment

CLEO is specifically seeking stories of evolving engineering efforts, including both maturing and already-implemented photonics technologies. Especially desired are introductions to and demonstrations of new products (without an accompanying overt sales pitch) or existing products with new capabilities; optical technologies at work in field situations, such as advanced sensors, metrology systems and the like; novel technologies useful to material fabricators and manufacturers; optical technologies useful in the design of system controls; and clinical applications of new or improved photonics-based sensors, cutting tools, or therapeutic approaches. The Society also is seeking exhibitions of optical engineering, especially hardware with new or significantly improved sensors, optical components and subsystems, optical designs for optical or electro-optical systems and subsystems; novel (or advancements to existing) optical system control/processing algorithms that enable new technical capabilities; new optics designs and measurement techniques; and advanced optics-based diagnostics systems.

Submitted papers are reviewed, with an eye toward “uniqueness, impact of the work, and how the work advanced the state of the art.”

So, if you have a choice bit of technology you’d like to show off to a wide-eyed group of people at next year’s meeting, heed the call for papers (http://www.cleoconference.org/home/submissions/) being requested by CLEO. The deadline is 16 December at 17.00 GMT.

 

Apr 30
Iain McKinnie, Lockheed Martin Advanced Technology Center,  CLEO: Applications & Technology 2013 Program Chair

Iain McKinnie, Lockheed Martin Advanced Technology Center, CLEO: Applications & Technology 2013 Program Chair

This year’s CLEO Conference, sponsored by APS/Division of Laser Science, IEEE Photonics Society and the Optical Society features an expanding Applications & Technology Program focusing on the core areas of Biomed, Energy, Industrial and Government/National Science and Security Standards.  Tom Giallorenzi, OSA’s Science Advisor interviewed Iain Mckinnie, Program Chair, Applications & Technology to delve further into some of this year’s hot topics.

Tom Giallorenzi: Can you say a little bit about technology transitions that this meeting is fostering?

Iain McKinnie:      “………there are many great examples in the Applications and Technology conference that you can see, including quantum cascade lasers.  We have a plenary talk this year which we’re very excited about by Dr. Kumar Patel from Pranalytica who is also a professor at UCLA.  And he’s going to be talking about how those quantum cascade lasers – now room temperature and multi-watt lasers in the midwave and long wave infrared region – are impacting applications from civil aircraft defense via countermeasures, through to trace gas detection for a range of commercial security  and environmental applications.  So that’s one capability that’s transitioning.

There are many more.  In the energy area, we’re looking at increasing transition of broadband nitride semiconductor materials in solar cells and in extending the spectral range of LEDs down into the UV region from the visible region. We’re also seeing increasing transition of ultrafast lasers, which continue to enable advances in manufacturing from the macro to the micro down to the nano scale.  ……. I think that we keep the wow factor in the conference also, and that comes in via big science; with some of the facility class laser systems: electron beams being used to generate extremely short bursts of intense light, and being used to generate extremely broadband, broad spectral access from the UV right out far into the infrared region.  Also, we have a big emphasis this year on the National Ignition Facility and the latest progress that they have achieved in the extreme high field regime.  So, you know, I think as well as things that could have mass market applicability, it’s important that we keep our finger on the pulse of the really impressive landmark advances at the unique and high power end.

Tom Giallorenzi: Can you say a few words about the special symposia?

Iain McKinnie:      One thing we’re very consciously focused on in 2013 at CLEO A&T is to bring in a number of special symposia which we believe represents a pretty broad suite of the application space for lasers that’s emerging.  I mentioned already the symposium related to the national ignition facility.  We have a number of others.  One that we’re excited about at the extreme other end of the scale is a lab on a chip symposium this year where we’re really taking advantage of advances not only in laser and LED sources, but also in microfluidics and nanotechnology and a whole lot of related applications to really take the pulse of that field and get a sense for how lab on a chip is advancing.

Beyond that, we also have a special symposium that’s looking at how the advances in sources are impacting biomedical applications more broadly.  That’s looking at advances in, for example, multi-modal imaging –  and looking at how relatively new sources like super continuum sources are being transitioned over into the application space.  And that’s a good example where there’s a need for those sources to be quieter and so that then flows back to the laser developers to really work on tailoring those sources for those kinds of applications.  I see biomedicine really being one of our significant growth areas in applications in technology in the coming years. 

 For more information on CLEO: 2013, visit www.cleoconference.org.

Dec 25

Demonstration of phase gradient microscopy in thick-tissue with back-illumination suitable for endoscopic integration. (a,c,e) amplitude images (b,d,f) phase gradient images of mouse intestinal epithelium. From T. ford, J. Chu, and J. Mertz, Nature Methods, 9, 1195 (2012). Jerome Mertz, Boston Univeristy, among other biomedical researchers, will be presenting latest breakthroughs in endoscopic imaging during invited talks at CLEO 2013 Applications and Technology: Biomedical.

This post originally appeared on Jim’s Cleo Blog and is reproduced with the author’s permission.

In the last two months, I gained a much larger appreciation for optical technology. Abdominal pain and pressure sent me to a number of doctors’ visits and a handful of endoscopic procedures: an upper-GI endoscopy, a colonoscopy, and a capsule endoscopy (the video camera in a pill). Before these, the most serious medical procedure  I had was a setting of a broken arm from a failed skateboarding trick when I was 11 years old. The stomach pain frightened me. It was deep inside where I couldn’t see it or get at it and it was making daily tasks and living difficult. I was so relieved to be prescribed the first endoscopy and then the followup procedures. It gave me an element of control. The thought repeatedly running through my head before and after these procedures was, “how fortunate I am to live in the time I am in.”  The upper-GI procedure took  less than 15 minutes, was painless, and I found out immediately after that my esophagus and stomach looked healthy. Tests from biopsies less than a week later confirmed this was true. I had similar experiences with the other endoscopies. I was given amazing information about by internal organs in fairly non-invasive short outpatient visits. The figure below shows one of the video frames of my stomach.

Stomach tissue from my own recent upper-GI endoscopy using a conventional commercial endocscope.

Because my own work in ultrafast laser systems has applications in nonlinear endoscopic imaging, I have used the words “optical biopsy”  (the idea that tissue is cleverly analyzed with photons during the procedure instead of “barbarically” exised to be sent to a lab and analyzed later) and “non-invasive” in introductions to papers, talks, or in explanations to lab visitors how an ultrafast laser has relevance to the average person. In the promotion of ultrafast lasers for optical biopsy, I  have sometimes talked about how the time and effort it takes to run biopsied tissue through histology is long and arduous-it needs to be sliced thin and stained in order to be viewed with a conventional microscope, and then analyzed by an expert. The patient distressingly waits for a diagnosis and also pays a non-trivial sum of money for the professional time involved for analysis.

I couldn’t have imagined the importance of these motivations before my own endoscopic procedures. What was part of my ultrafast laser stump speech was suddenly very real and worthy. My own experiences were definitely non-invasive. What would have been my options when endoscopes were larger and bulkier? What would have been my options prior to widespread use of endoscopic diagnosis?  And though my waiting for histology was short, it was still difficult and definitely costly. What advantages will the next generations have as optical researchers and engineers push endoscopes to use more imaging modalities? Push them to smaller sizes and with more functionality? What peace of mind can we pass on?

No doubt many contributed talks to CLEO 2013 and postdeadline papers will address advances in endoscopic procedures, endoscopes, and catheter-based probes. Last year’s postdeadline session saw two papers on endoscopic imaging: one from a collaboration between John Hopkins Univeristy and Corning, Inc. led by Xingde Li for efficient, high-resolution nonlinear endomicroscopy and  the other from Chris Xu’s lab of Cornell University which piggy-backed wide-field one-photon imaging with high-resloution two-photon imaging in the same device for optical zoom capability.  There were also a number of contributed submissions regarding advances in endoscopy such as the work by Adela Ben-Yakar’s group of the University of Texas at Austin whose endoscope used the same ultrafast laser for two-photon imaging for targeting tissue and subsurface precision microsurgery  through athermal ablation. Last year’s CLEO also hosted an invited talk by Brett Bouma, pioneer of Optical Coherence Tomography (OCT), on translating OCT into GI endoscopy.

This year’s invited speakers in CLEOs Applications and Technology: Biomedical will also be addressing future directions on endoscopes and  endoscopic procedures. Invited speaker Jerome Mertz of Boston University will be discussing his work on phase contrast endomicroscopy which was just published in this week’s  Nature Methods. His technique cleverly uses two diametrically opposed off-axis sources to allow oblique back-illumination  in a reflection mode geometry. Traditionally phase contrast microscopy using oblique illumination requires transillumination and is therefore not suitable for in vivo imaging. Mertz’s back-illumination technique allows his microscope to be miniaturized and integrated into an endoscope for which the source and detection optics must reside on the same side of the sample. Unlike traditional oblique illumination phase contrast, Mertz’s technique can be used to image thick samples.

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Sep 06

Artist Rendering of ChemCam Laser Analysis on Mars Science Laboratory. From libs.lanl.gov/ChemCam.html

This post originally appeared on Jim’s Cleo Blog and is reproduced with the author’s permission.

What do front man for the Black Eyed Peas, Will.i.am, and ultrafast optical pulses have in common? They are both playing crucial role on the newest Mars rover mission. On August 28, Will.i.am’s song “Reach for the Stars” was the first musical composition to be transmitted to Earth from another planet, in this case from Curiosity, twelve days after its  Seven Minutes of Terror landing, complete with state-of-the-art supersonic parachute and sky-crane. I’m still a bit shocked at this science fictionesque feat of impressive engineering seeming to border on hubris. Really, a sky-crane? Really?

While Will.i.am’s  interplanetary music transmission is playing a critical role in science and engineering outreach as part of google+ and Lockheed Martin sponsored initiative SYSTEM (Stimulating Youth for Science Technology Engineering and Math), ultrafast optics is playing a critical role for analyzing the geology of the martian surface. On August 19, ChemCam, an instrument that is a part of the Mars Science Laboratory on board Curiosity, ablated part of a rock with ultrafast optical laser pulses and performed chemical analysis on the emitted plasma to determine rock and soil composition, a first for exogeology. Though the technique, laser induced break-down spectroscopy (LIBS), is almost as old as the laser itself, it has never been performed on another planet. What makes LIBS so useful for Mars exploration is that as an active remote sensing technique, no physical contact needs to be made with the rock or soil under test, including cleaning the sample area.

The previous Mars rovers required a rock abrasion tool to remove dust and outer layers to analyze the more interesting unweathered interior of rock and soil samples. On Curiosity, initial pulses “clean” the area and subsequent pulses create the plasma of interest whose spectrum is to be analyzed. For this instrument standoff distances can be as far as 7 m. The LIBS instrument has been combined with a Remote Micro-Imager (RMI) to give contextual information around the approximate 0.5 mm LIBS interrogation points in a single instrument called ChemCam. The figure below shows the precision of the laser system as well as the resolution of the Micro-Imager at 3 m stand-off.  The choice to burn precision holes in the U.S. dollar and Euro (near Toulouse, France on the Euro map) is in homage to locations of the collaborating institutions  Los Alamos National Laboratory, Centre National d’Etudes Spatiales, and Centre National de la Recherche.

Demonstration of ChemCam’s shooting accuracy and micro imager resoltion at 3 m standoff after ablating holes in U.S. and European currency respectively. The inset (lower left) shows the difference image. Image from poster “Progress on Calibration of the ChemCam LIBS Instrument on the Mars Science Laboratory Rover,” by principle investigator R.C. Weins, 2010.

 

 

 

 

 

 

 

 

 

Besides the ultrafast laser system, ChemCam is a goldmine of optical engineering and instrumentation. There is honestly something for almost any kind of optical scientist on this instrument. Details can be found both on the ChemCam website and in a review of the instrument suite (an easy geeky read which I had trouble putting down). The laser and imaging optics reside in the mast of ChemCam (the seeming periscope-like eye of the rover) and the spectrometers and supporting equipment live in the body unit. The mast and body are connected by optical fiber.

Schematic of ChemCam. From “The ChemCam Instrument Suite on the Mars Science Laboratory Rover: Body Unit and Combined System Tests,” Space Sci. Rev., DOI 10.1007/s11214-012-9902-4, (2012).

 

 

 

 

 

 

 

 

 

 

 

 

 

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Mar 30

(One of seventeen youtube shorts from the program chairs highlighting hot topics for CLEO 2012)

This post originally appeared on Jim’s CLEO Blog and is reproduced with permission from the author.

For a few years now CLEO conference organizers have been posting youtube shorts highlighting contributed talks, symposia, research trends, and any new or unique directions for the upcoming conference. This year there are seventeen videos from the program chairs, all worth watching. However, for those who prefer text over A/V, I thought it might be helpful to highlight the highlights here.

Conference Program Stats

-The 2012 program has been selected from a record number of submissions.

-In just its second year, CLEO’s new Technology and Applications Conference saw a 50 % increase in submissions.

-350 papers, 15 % of all submissions, live in the subcommittee sections “Nano-optics and Plasmonics” or “Micro- and Nano-Photonic Devices”

-Subcommittee section: “Fiber Amplifiers, Lasers and Devices” was the single committee that received the most submissions

CLEO Applications and Technology: Government and National Science, Security and Standards Applications

In his youtube short, subcommittee Chair Ian Mckinnie of Lockheed Martin Coherent Technologies briefly discusses the two tracks of this subcommittee: 1) Ultrafast Laser Applications and 2) Instrumentation and Sensing.

Mckinnie talks about how the ultrafast program covers a broad range ultrafast laser applications spanning those performed at large facility-class systems to those on a bench top or operating table. These are exemplified by the tutorial talk, AW3J1, “Enabling Science at the Advanced Light Source X-ray Facility” that will be given by Roger Falcone of Lawrence Berkeley National Laboratory from 4:30-5:30 pm on May 9, and the invited talk AW3J4, “Applications of Ultrafast Lasers” by Mike Mielke of Raydiance Inc., also on May 9, but from 6:00-6:30 pm

The Advanced Light Source (ALS) is a large synchrotron source that produces laser light over an extremely broad spectrum including the hard-to-reach soft x-ray region. Falcone will be discussing the use of the coherent radiation at this user-facility for applications such as precise material processing and biomedical research.

On the other hand, Mielke will be discussing the use of compact fiber systems for micromachining and laser surgery. See blog post “Machining with Ultrafast Pulses” for some stunning videos and more information on these compact micromachining systems.

On the remote sensing side, Massayuki Fujita, from the Institute of for Laser Technology in Osaka, will be giving an invited talk on an application of remote sensing not typically found in the CLEO conference program- nondestructive inspection for heavy industrial processes. Fujita’s talk, ATuG3 “Nondestructive Inspection for Heavy Construction” can be heard on Tuesday May 8, at 2:30 pm.

CLEO Applications and Technology: Industrial Applications

In his video short, subcommittee chair Eric Mottay of Amplitude Systemes discuses the two major trends of the Industrial Applications subcommittee: 1) micro- and nanofabrication techniques and 2) applications of graphene.

Talks in the latter category can be found in a joint session with CLEO: Science and Innovation subcommittee six in session “Graphene and Carbon Advanced Photonic Materials” which will be held form 11:00am-1:00 pm on May 8. This session will host talks presenting graphene-based devices such as detectors, modulators, and tunable resonators. Recall that Andre Geim and Konstantin Novoselov were awarded the 2010 Nobel Prize for showing the “exceptional” properties of graphene such as it being simultaneously the thinnest and strongest material, having better electrical conductivity than copper, better heat conduction than all other known materials, and having nearly 100 % transparency yet an extremely high density (so dense helium atoms cannot pass through). Be sure to see how this “magical” material is being translated into devices that may be on the market in the next three to five years.

On the other hand, the invited talks for this subcommitee all center around micro- and nano- fabrication processes. Arnold Gillner of the Fraunhofer Institute will discuss how ultrafast lasers can be used for surface processing at the micro- and nanoscale level for applications in light guiding, fabrication of low friction surfaces, or wear-resistant surfaces. His talk, ATu3L1, “Micromanufacturing and nano surface functionalisation with ultrashort pulsed lasers” is scheduled for May 8, at 4:30 pm. Additionally, Paul Webster from Queen’s University will be discussing online monitoring during fabrication, particularly concerning the control of depth, in invited talk ATu3L5, “Inline Coherent Imaging: Measuring and Controlling Depth in Industrial Laser Processes,” on May 8, at 5:45 pm and Rick Russo from Lawrence Berkeley National Laboratory will be speaking about real-time spectroscopy of a sample after it has been turned into a plasma through laser ablation in talk, AW1H3 “Laser Plasmas for Spectrochemistry” on May 9, at 11:00 am.

CLEO Applications and Technology: Energy and Environment

In his video short, subcommittee chair Christian Wetzel from Rensselaer Polytechnich Institute discusses two trends… click here to read the full original post

Mar 26

This post originally appeared on CLEO BLOG by Frank Kuo and is reproduced with permission from its author.

Figure 1. A generic ferrimagnet, composed of Fe and Gd, shows the alignment of magnetic moment. Courtesy of I.Radu et al., Nature 472 205 (2011).

The principle of magnetic storage used by most hard drives is an important pillar in the evolution of modern digital world. Before the advent of flash memory, it dominated the way we saved our data. Simply speaking, binary information (0 or 1) is presented by small magnets pointing forward (0) or backward (1); let’s say the north is the head. Writing the data is by changing the pointing directions of these magnets, usually fulfilled by an electric coiled wrapped head (by applying the current into the head, you create a strong external magnetic field that realign the directions of the small magnets in the hard drive, one at a time). In addition, packing in as many magnets as possible in a limited volume will define the capacity of a hard drive, and this is improving ever since the first device available. Imaging the first computer I had came with a hard drive of 400 MB, and now a decent one has a few TB storage capacities. By comparing the number, you can realize how much effort and advances in the business of data storage. For a very nice introduction, you can find at hard drive 101: magnetic storage.

A nice paper where ultrafast laser pulses (sub 100 fs) instead of external magnetic field are used to write data intrigued my curiosity. I know immediately that it is the heating effect that causes the change of the magnetization of the small magnets in the hard drive. But for me, the heat has no directionality, how it can tell the magnet to point forward or backward. It should just erase the information since an ultrafast laser pulse can easily create a hot environment above Curie temperature where the magnetization is destroyed. So in my mind, an ultrafast laser is a hard drive terminator, not a hard drive writer. Driven by this curiosity, I dug in to find out, and this is how:

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Feb 24

Schematic of pump-probe experiment to investigate femtosecond time-scale demagnetization on a magnetic film; from Bigot et al., Nature, 465, 458 (2010).

This post originally appeared on Jim’s Cleo Blog and is reproduced with permission from its author.

As we await decisions on contributed papers in the next couple of weeks and for the technical program to be scheduled, the list of tutorials and invited talks for CLEO 2011 is rounding out. Two provoking titles that recently caught my eye were tutorial talks “Femtomagnetism” to be given by Jean-Yves Bigot from CNRS in Strasbourg, France under CLEO: QELS Fundamental Science 4: Optical Interactions with Condensed Matter and Ultrafast Phenomena as well as “Therapeutic Applications of Light: Photodynamic Therapy, the Killer and Low Level Light Therapy, the Healer” to be given by Michael Hamblin from Massachusetts General Hospital, under CLEO: Applications & Technology 1: Biomedical.

In a recent Nature article, Bigot et al. describe short time-scale, spin-orbit dynamics during femtosecond, laser-induced demagnetization. Using a femtosecond pump pulse to quickly demagnetize a ferromagnetic thin-film immersed in a magnetic field, Bigot and his collaborators extract information about the spin and orbital angular momentum as a function of time in a cross-correlation technique using x-ray pulses (See Fig.1). Spin and orbital angular momentum contributions during the process are measured by time-resolved x-ray magnetic circular dichroism (XMCD), a technique in which circularly polarized x-rays absorb in different proportions at different energies depending on the spin and orbital angular contributions of the material. This recent work investigates the magnetism dynamics in thin films whose magnetization is perpendicular to the plane of the film- a class of materials sought after for high-density data storage, and for which spin-orbit coupling plays a large role.

Professor Hamblin’s work on the other hand uses light in a very different way- to activate chemicals that can target and selectively kill harmful cells like infectious microbes or malignant cancer cells (photodynamic therapy), as well as to activate the production of intrinsic detoxifying chemicals within damaed cells to stimulate tissue healing (low level light therapy). In photodynamic therapy (PDT), photosensitizers are introduced into the body locally or topically and taken-up by the harmful cells. Illuminating the targeted cells with light excites the photosensitizers and produces reactive oxygen species harmful to the targeted cell.

Plots showing enhanced cellular uptake of the photosensitizer ZnPc-(Lys) compared with other sensitizers, and corresponding images of cells; from Hamblin et al., ChemMedChem, 5, 890, (2010).

One of the aims of Hamblin’s group is to create more efficient photosensitizers- ones that are more readily taken up by targeted cells and that are more lethal. Hamblin recently synthesized a photosensitizer, Pentalysine Beta-Carbonylphthalocyanine Zinc (ZnPc-(Lys)), that showed better cellular up-take, better selectivity to targeted cells, and a 20 times increase in photo-toxicity. Figure 2. shows the increase in uptake compared to conventional sensitizers.  For more information on killing and healing power of light, visit Professor Hamblin’s very accessible and informative web pages. Better yet, be sure to attend the tutorial on phototherapy… For the full original post, click here.

Sep 08

The nerdy license plate of fellow Augustana College physics professor Cecilia Vogel, referencing the famous 1935 Phys. Rev. paper by Einstein, Podolsky, and Rosen which introduced the idea of entanglement and questioned the completeness of a quantum mechanical description of reality

This post originally appeared on Jim’s Cleo Blog and is reproduced with permission from its author.

Looking back through some of the literature in photonics and optics published this summer, I was most fascinated by three experiments concerning reliable generation of entangled photons. Two groups, one from China1 and another from Vienna2, showed independent reports of heralded generation of entangled photon pairs. Another, from Toshiba of Europe , demonstrated ‘on-demand’ entangled photons from a quantum dot embedded inside an LED, making an entangled-LED or more simply, ELED3. These works have been nicely summarized in the News and Views section in the August issue of Nature Photonics:Entangled photons report for duty,” by Pieter Kok4 and “A spooky light-emitting diode” by Val Zwiller5 .

The recent News and Views articles by Kok and Zwiller stirred the inner physicist within me, and sent me down a path of literature searching too detailed, too mathy , and too long for a blog post. However, I’ve attempted to give my own understanding of how the exciting work of heralded and on-demand entangled photon sources can be put into a broader context. If you’re a beginner like me and want more information on the fundamentals of quantum information, I recommend Kok’s website and review article6, Gisin’s review7, and Dehlinger’s article geared for setting up entanglement experiments for the advanced undergraduate laboratory curriculum8.

Whether or not you’re a practicing quantum mechanic, you likely know that entanglement is a crucial ingredient for quantum information processing. Entanglement using photons may be the best method for practically achieving quantum computing and for quantum communication due to their coherence, low transmission loss, and ease of manipulation. The most widely used method for generating entangled photon-pairs is through spontaneous parametric down-conversion in a nonlinear crystal (SPDC). This technique is so robust that it has recently been employed in a number of undergraduate teaching labs to help physics students understand the photonic nature of light and the non-intuitive implications of quantum mechanics8,9,10.

Beating the Odds

Figure 1. reproduced and adapted from ref. 4. Creating entangled photon pairs. (a) In normal operation, a parametric down-converter (PDC) produces an unknown number of entangled photon pairs in each pulse. Detectors must then ‘post-select’ the correct events that contain exactly one pair. (b) The basic setup used by Pan and Walther's lab; a particular four-photon detection event can occur only when three pairs are present, with the remaining two entangled photons propagating freely. This creates precisely one ‘heralded’ entangled photon pair.

The problem with SPDC is that the process of pair generation is probabilistic. More often than not, zero or multiple pairs are generated, see Fig 1 (a). Like a game of black-jack at a Vegas card table, more often than not you don’t get the cards want, and so more often than not, the house wins. However, if you are clever and can count cards, you can guarantee a win even though the odds are against you. You aren’t changing the probability distribution of what is being dealt, you are just predicting what will be played. You can select which cards you want and pass on others without having to see their face values. In the language of quantum entanglement, you would be ‘heralding’ or announcing the cards you want before they are dealt.

The heralded entangled photon source produced by Jian-Wie Pan’s lab in China1 and Philip Walther’s lab in Vienna2 was done through clever counting. Both groups used a setup similar to Fig 1. (b) such that when three photon pairs were generated simultaneously by SPDC, two of the pairs would be ‘peeled off’4 by the beam splitters, and remaining would be guaranteed to be a single entangled pair. Essentially, the simultaneous firing of four detectors at the outputs of the ‘peel off’- beam splitter herald a single remaining entangled photon pair. You have to wait for a three-photon pair event, but you can be guaranteed an entangled output.

Fig. 2 (a) Reproduced and adapted from from ref. 3. Schematic of the active region of the ELED, showing the emission of a polarization entangled photon pair through the biexciton cascade. (b) reproduced from ref. 5. Optical microscope image of the from Toshiba Europe.

Another way to beat the house is to change the probability of cards drawn- use your own deck. Salter et al.3 from the Shileds group of Toshiba Europe essentially took this approach to creating entangled photon pairs by using an entirely different physical mechanism than SPDC. Using the radiative decay of the biexciton state in a quantum dot Fig. 2 (a) , the Toshiba group created an ‘on-demand’ entangled source. The biexciton state is created by the capture of two electrons and two holes. So long as the two excitons are degenerate in energy (no fine structure splitting) the output will be entangled. In fact, one of the experimental hurdles overcome by the Tohsiba group was to grow quantum dots emitting photons of the right energy, near 1.4 eV (887 nm), in order to have very small fine-structure splitting. Because the source is not probabilistic and no clever counting setups are needed, it is referred to as ‘sub-Poissonian’5. What makes Salter’s work so hot is that the on-demand source is driven electrically. No bulky pump lasers are needed like they are for an SPDC source. The entangled-LED, or ELED, could possibly be scaled down to submicron sizes for on-chip integration5, see the microscope image in Fig. 2 (b)…For references and to read the full post, click here.

May 20

From CTuII2

This post originally appeared on Jim’s Cleo Blog and is reproduced with permission from its author.

Khanh Kieu, from University of Arizona, began his talk, CTuII2,”Generation of sub-20fs pulses from an all-fiber carbon nanotube mode-locked laser system” emphasizing the importance of saturable absorbers (SA) in mode-locked lasers. The SA is the device that is responsible for locking the modes in a laser cavity, thereby allowing the creation of pulses. Without one, you’d just have a continuous wave laser. In general, a saturable absorber is any device that transmits higher intensities of light at expense of lower intensities. They can be active, passive, real, or artificial. In ultrafast fiber-lasers, the typical SA of choice is a semiconductor saturable absorber mirror, SESAM,  (a real SA relying on material response) or nonlinear polarization evolution, NPE, (an artificial one making use of polarization tricks). Kieu’s point is that it makes sense to spend time developing the component of the mode-locked laser that is responsible for mode-locking.

Kieu and his collaborators at Arizona have been doing just that by developing SAs using carbon nanotubes. Though not the primary motivation, Amer Nevet, from Technion in Haifa, and his collaborators have also been developing effective SAs  by showing the first example of two-photon gain in semiconductors, CKK1, “Direct Observation of Two-Photon Gain in Semiconductors.” ...Read the full post by clicking here.

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