By James Van Howe
This post originally appeared on Jim’s Cleo Blog and is reproduced with permission from its author.
On Thursday May 5, from 8pm- 10pm, conference goers will be madly dashing from ballroom to ballroom to hear the latest breaking optics research- it’s like a geeky Black Friday for optical science. There are 36 talks in total, but because they are spread out among three sessions, you realistically can only hear 12. Trying to see more requires cat-like agility to maneuver around standing-room-only crowds. Good thing postdeadline abstracts were recently posted. Be sure to look through the agenda of sessions and plan
Fig. 1. From P. Del'Haye, Nature, 450 1214, (2007). a) frequency comb spectrum, b) degenerate and non-degenerate four-wave-mixing among cavity modes, c) SEM image of torroidal microcavity
This year’s sessions include record breaking feats typical of CLEO postdealine papers: an ultralow 181 nA lasing threshold in a nanocavity laser (PDPA1), a whopping 4176% W-1cm-2 conversion efficiency for parametric fluorescence in a diode laser (PDPA3), a limit-pushing 1.5 mm imaging depth in a mouse brain cortex using a two-photon microscope (PDPB3), Mid-IR to keV X-ray supercontinuum generation (PDPC12), a noise figure less than 3 dB in a phase sensitive amplifier (PDPB10), and many others.
Though the sessions will host a wide variety of topics in fundamental and applied optics, some themes that emerge from this year’s postdeadline abstracts are papers that demonstrate broadband frequency generation, biomedical imaging (the postdeadline subcategory CLEO: Applications & Technology 1: Biomedical has the most papers of the three sessions), and nanoscale lasers and nano-photonic devices.
One of the papers on broadband frequency generation, PDPA4, “Mid-Infrared Frequency Combs Based on Microresonators,” by Wang et al. from a German, Swiss, and French collaboration (note one of et al’s s is Nobel Laureate Theodor Hansch), builds on previous work reported in a 2007 Nature paper to produce a monolithic comb generator in the Mid-IR. The reason for the microresonator is to get rid of the big Ti:Sapphire laser typically used to generate frequency combs in order to scale down cost, complexity and size of the comb generator. The high-Q microresonator, an example of which is shown in the Fig. 1, requires a simple CW pump. Besides being smaller, simpler, and potentially much cheaper, the microresonator has the advantage of producing comb spacings greater than 500 GHz (something unattainable by comb generators that use ultrafast pulsed seed sources like the Ti:Sapph).
Fig. 2. From Daylight Solutions, interesting molecules arranged by peak absorption wavelength
One compelling reason for building a comb generator in the Mid-IR is for ultrasensitive, broadband spectroscopy in an interesting spectral region for which there is a dearth of laser sources. Figure 2. from Daylight Solutions (CLEO booth 1526), a company that fabricates quantum cascade lasers between 3.0 and 20.0 microns, sorts molecules of interest by their peak spectral absorbance. These molecules are interesting for environmental monitoring (ozone, water, methane, carbon dioxide), threat and standoff detection (TNT, TATP, VX), and biomedical spectroscopy (glucose).
Fig. 3. From Kobat et al., Optics Exp., 17, 13354, (2009). a) Two-photon image of a mouse cortex with 775 nm excitation and 1280 nm excitation. b) Attenuation of fluorescence vs. depth for 775 nm and 1280 nm excitation.
New additions to this year’s postdeadline session are subcategories in CLEO: Applications and Technology, most notably CLEO: Applications & Technology 1: Biomedical. The four papers in this subcategory demonstrate pushing the limits on resolution, high-speed image acquisition, or penetration depth for different microscopic techniques. PDPB3, “In vivo two-photon imaging of cortical vasculature in mice to 1.5-mm depth with 1280 nm excitation,” by Kobat et al. shows record imaging depth in a mouse brain cortex using two-photon microscopy by cleverly using long-wavelength excitation. Typical two-photon microscopes use 800 nm, ultrafast pulses from a Ti:Sapphire laser to excite the tissue to be imaged. Photons may not make it to the depth of interest because of absorption or scattering. In brain tissue, scattering dominates over absorption between 350 nm -1300 nm. By using a longer excitation source, more photons can make it to the target allowing for deeper imaging…For the full original post, click here.
Posted: 21 April 2011 by
James Van Howe
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