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Is it possible to form an image using light produced by stimulated emission? Here we study light scatter off an assembly of excited chromophores. Due to the Optical Theorem, stimulated emission is necessarily accompanied by excited state Rayleigh scattering. Both processes can be used to form images, though they have different dependencies on scattering direction, wavelength and chromophore configuration. Our results suggest several new approaches to optical imaging using fluorophore excited states.
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Stimulated Raman spectroscopy has become a powerful tool to study the spatiodynamics of molecular bonds with high sensitivity, resolution and speed. However, sensitivity and speed of state-of-the-art stimulated Raman spectroscopy are currently limited by the shot-noise of the light beam probing the Raman process. Here, we demonstrate an enhancement of the sensitivity of continuous-wave stimulated Raman spectroscopy by reducing the quantum noise of the probing light below the shot-noise limit by means of amplitude squeezed states of light. Probing polymer samples with Raman shifts around 2950 $cm^{-1}$ with squeezed states, we demonstrate a quantum-enhancement of the stimulated Raman signal-to-noise ratio (SNR) of 3.60 dB relative to the shot-noise limited SNR. Our proof-of-concept demonstration of quantum-enhanced Raman spectroscopy paves the way for a new generation of Raman microscopes, where weak Raman transitions can be imaged without the use of markers or an increase in the total optical power.
We have observed laser-like emission of surface plasmon polaritons (SPPs) decoupled to the glass prism in an attenuated total reflection setup. SPPs were excited by optically pumped molecules in a polymeric film deposited on the top of the silver film. Stimulated emission was characterized by a distinct threshold in the input-output dependence and narrowing of the emission spectrum. The observed stimulated emission and corresponding to it compensation of the metallic absorption loss by gain enables many applications of metamaterials and nanoplasmonic devices.
The spatial resolution and fluorescence signal amplitude in stimulated emission depletion (STED) microscopy is limited by the photostability of available fluorophores. Here, we show that negatively-charged silicon vacancy (SiV) centers in diamond are promising fluorophores for STED microscopy, owing to their photostable, near-infrared emission and favorable photophysical properties. A home-built pulsed STED microscope was used to image shallow implanted SiV centers in bulk diamond at room temperature. The SiV stimulated emission cross section for 765-800 nm light is found to be (4.0 +/- 0.3) x 10^(-17) cm^2, which is approximately 2-4 times larger than that of the negatively-charged diamond nitrogen vacancy center and approaches that of commonly-used organic dye molecules. We performed STED microscopy on isolated SiV centers and observed a lateral full-width-at-half-maximum spot size of 89 +/- 2 nm, limited by the low available STED laser pulse energy (0.4 nJ). For a pulse energy of 5 nJ, the resolution is expected to be ~20 nm. We show that the present microscope can resolve SiV centers separated by <150 nm that cannot be resolved by confocal microscopy.
We present a quantum optics approach for describing stimulated parametric down conversion in the two type-I crystal sandwich configuration, which allows for parametric interaction of vector vortex beams. We analyze the conditions for which phase conjugation of the seed vector beam occurs. We then use two strategies for defining generalized Stokes parameters to describe phase conjugation of vector vortex beams. These allow for geometrical representations, such as higher-order Poincare spheres. Our results are useful for description and design of stimulated and spontaneous parametric down conversion experiments with vector vortex beams.
Silicon-based light sources including light-emitting diodes (LEDs) and laser diodes (LDs) for information transmission are urgently needed for developing monolithic integrated silicon photonics. Silicon doped by ion implantation with erbium ions (Er$^{3+}$) is considered a promising approach, but suffers from an extremely low quantum efficiency. Here we report an electrically pumped superlinear emission at 1.54 $mu$m from Er/O-doped silicon planar LEDs, which are produced by applying a new deep cooling process. Stimulated emission at room temperature is realized with a low threshold current of ~6 mA (~0.8 A/cm2). Time-resolved photoluminescence and photocurrent results disclose the complex carrier transfer dynamics from the silicon to Er3+ by relaxing electrons from the indirect conduction band of the silicon. This picture differs from the frequently-assumed energy transfer by electron-hole pair recombination of the silicon host. Moreover, the amplified emission from the LEDs is likely due to a quasi-continuous Er/O-related donor band created by the deep cooling technique. This work paves a way for fabricating superluminescent diodes or efficient LDs at communication wavelengths based on rare-earth doped silicon.
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