We present a unique confocal microscope capable of measuring the Raman and Brillouin spectra simultaneously from a single spatial location. Raman and Brillouin scattering offer complementary information about a material's chemical and mechanical structure, respectively, and concurrent monitoring of both of these spectra would set a new standard for material characterization. We achieve this by applying recent innovations in Brillouin spectroscopy that reduce the necessary acquisition times to durations comparable to conventional Raman spectroscopy while attaining a high level of spectral accuracy. To demonstrate the potential of the system, we map the Raman and Brillouin spectra of a molded poly(ethylene glycol) diacrylate (PEGDA) hydrogel sample in cyclohexane to create two-dimensional images with high contrast at microscale resolutions. This powerful tool has the potential for very diverse analytical applications in basic science, industry, and medicine.

Two-dimensional stimulated Brillouin scattering microscopy is demonstrated for the first time using low power continuous-wave lasers tunable around 780 nm. Spontaneous Brillouin spectroscopy has much potential for probing viscoelastic properties remotely and non-invasively on a microscopic scale. Nonlinear Brillouin scattering spectroscopy and microscopy may provide a way to tremendously accelerate the data aquisition and improve spatial resolution. This general imaging setup can be easily adapted for specific applications in biology and material science. The low power and optical wavelengths in the water transparency window used in this setup provide a powerful bioimaging technique for probing the mechanical properties of hard and soft tissue.

The ability to control the propagation of light through scattering media is essential for atmospheric optics, astronomy, biomedical imaging and remote sensing. The optimization of focusing light through a scattering medium is of particular interest for the case of highly scattering materials. Optical wavefront beam-shaping plays a critical role in optimizing such a propagation; however, an enormous field of adjustable parameters makes the overall task complicated. Here, we propose and experimentally evaluate several variations on the standard continuous sequential algorithm that hold a promise of revealing new, faster and more efficient optimization algorithms for selecting an optical wavefront to focus light through a scattering medium. We demonstrate that the order in which pixels are chosen in the continuous sequential algorithm can lead to a 2-fold decrease in the number of iterations required to reach a given enhancement.

Spontaneous Raman scattering is a powerful tool for chemical sensing and imaging but suffers from a weak signal. In this Letter, we present an application of adaptive optics to enhance the Raman scattering signal detected through a turbid, optically thick material. This technique utilizes recent advances in wavefront shaping techniques for focusing light through a turbid media and applies them to chemical detection to achieve a signal enhancement with little sacrifice to the overall simplicity of the experimental setup. With this technique, we demonstrate an enhancement in the Raman signal from titanium dioxide particles through a highly scattering material. This technique may pave the way to label-free tracking using the optical memory effect.

Raman imaging is a powerful method to identify and detect chemicals, but the long acquisition time required for full spectroscopic Raman images limits many practical applications. Compressive sensing and compressed ultrafast photography have recently demonstrated the acquisition of multi-dimensional data sets with single-shot detection. In this Letter, we demonstrate the utilization of compressed sensing for single-shot compressed Raman imaging. In particular, we use this technique to demonstrate the identification of two similarly white substances in one image via the recovered two-dimensional array of Raman spectra. This technique can be further extended by coupling the compressed sensing apparatus with a microscope for compressed hyperspectral imaging microscopy.

We study backward cooperative emissions from a dense sodium atomic vapor. Ultrashort pulses produced from a conventional amplified femtosecond laser system with an optical parametric amplifier are used to excite sodium atoms resonantly on the two-photon 3S 1 2 -4S 1 2 transition. Backward superfluorescent emissions (BSFEs), both on the 4S 1 2 -3P 3 2 and 4S 1 2 -3P 1 2 transitions, are observed. The picosecond temporal characteristics of the BSFE are observed using an ultrafast streak camera. The power laws for the dependencies of the average time delay and the intensity of the BSFEs on input power are analyzed in the sense of cooperative emission from nonidentical atomic species. As a result, an absolute (rather than relative) time delay and its fluctuations (free of any possible external noise) are determined experimentally. The possibility of a backward swept-gain superfluorescence as an artificial laser guide star in the sodium layer in the mesosphere is also discussed.

Optical second harmonic generation is a fundamental nonlinear effect with a large impact on laser technology and optical imaging/sensing. For most practical applications of second harmonic generation, high conversion efficiency is required. However, many techniques used to achieve high efficiency are limited to fabrication methods and optical energy requirements. Here, we investigate and demonstrate substantial enhancement in the conversion efficiency of second harmonic generation in a nonlinear crystal via the application of wavefront shaping. In a one-dimensional understanding of second harmonic generation, a phase offset applied to the fundamental wave has no effect on the intensity of the generated light. We show that when the pump field is not a plane wave, enhanced conversion efficiency can be controlled by the application of a phase mask to the fundamental beam. This investigation of the dependence of conversion efficiency upon the transverse phase profile of the incident pump laser yields the promise of new ways to enhance nonlinear generation with limited optical energy and without the need for specific fabrication techniques.

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