Marius A. Albota

TWO-PHOTON FLUORESCENCE EXCITATION CROSS SECTIONS OF BIOMOLECULAR PROBES FROM 690 TO 960 NM

We report on two-photon fluorescence excitation (TPE) action cross sections for five widely used molecular fluorophores. Measurements were performed by use of ultrashort (~100-fs) Ti:sapphire pulsed excitation over the range 690-960 nm. TPE spectra were obtained by comparison with a fluorescein calibration standard. Large cross sections were found for the cyanine reagent Cy 3 (~140 GM) and for Rhodamine 6G (~150 GM), both at 700 nm [1 GM = 10(-50) (cm(4) s)/photon]. Several fluorophores show interesting and desirable blue shifts with respect to twice the one-photon absorption wavelength. Fluorophore fluorescence intensities showed no significant departure (?4%) from quadratic illumination power dependence, indicating genuine two-photon processes. Implications of these measurements for two-photon laser-scanning microscopy are discussed.

Three-dimensional imaging laser radar with a photon-counting avalanche photodiode array and microchip laser

We have developed a threedimensional imaging laser radar featuring 3-cm range resolution and single-photon sensitivity. This prototype direct-detection laser radar employs compact, all-solid-state technology for the laser and detector array. The source is a Nd:YAG microchip laser that is diode pumped, passively Q-switched, and frequency doubled. The detector is a gated, passively quenched, two-dimensional array of silicon avalanche photodiodes operating in Geigermode. After describing the system in detail, we present a three-dimensional image, derive performance characteristics, and discuss our plans for future imaging three-dimensional laser radars.

Efficient single-photon counting at 1.55 µm by means of frequency upconversion

We demonstrate efficient single-photon detection at 1.55 microm by means of sum-frequency mixing with a strong pump at 1.064 microm in periodically poled lithium niobate followed by photon counting in the visible region. This scheme offers significant advantages over existing InGaAs photon counters: continuous-wave operation, higher detection efficiency, higher counting rates, and no afterpulsing. We achieved single-photon upconversion efficiency of 90% at 21.6 W of circulating power in a resonant pump cavity with a 400-mW Nd:YAG laser. We observed high background counts at strong circulating pump powers due to efficient upconversion of pump-induced fluorescence photons.

Two-Photon Coincident-Frequency Entanglement via Extended Phase Matching

We demonstrate a new class of frequency-entangled states generated via spontaneous parametric down-conversion under extended phase-matching conditions. Biphoton entanglement with coincident signal and idler frequencies is observed over a broad bandwidth in periodically poled KTiOPO4. We demonstrate high visibility in Hong-Ou-Mandel interferometric measurements under pulsed pumping without spectral filtering, which indicates excellent frequency indistinguishability between the down-converted photons. The coincident-frequency entanglement source is useful for quantum information processing and quantum measurement applications.

Efficient and spectrally bright source of polarization-entangled photons

We demonstrate an efficient fiber-coupled source of nondegenerate polarization-entangled photons at 795 and

Three-dimensional laser radar with APD arrays

1609\phantom{\rule{0.3em}{0ex}}\mathrm{nm}

Efficient generation of tunable photon pairs at 0.8 and 1.6 µm

using bidirectionally pumped parametric down-conversion in bulk periodically poled lithium niobate. The single-mode source has an inferred bandwidth of

Optimal Rebalancing for Institutional Portfolios

50\phantom{\rule{0.3em}{0ex}}\mathrm{GHz}

Laser vibrometry from a moving ground vehicle.

and a spectral brightness of

Single photon detection of degenerate photon pairs at 1.55 μm from a periodically poled lithium niobate parametric downconverter

300\phantom{\rule{0.3em}{0ex}}\text{pairs}∕(\mathrm{s}\phantom{\rule{0.2em}{0ex}}\mathrm{GHz}\phantom{\rule{0.2em}{0ex}}\mathrm{mW})