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Bojesen Christensen posted an update 6 months, 2 weeks ago
We have directly generated optical pulses having a duration of 0.56 ps with a peak power of 25 W by gain switching of multi-section semiconductor lasers in which the optimized lengths of the absorption and gain regions were 50 and 200 µm, respectively. Even though the experiment was conducted via impulsive optical pumping at a low temperature, we observed that the multi-section gain switching suppresses the low-energy tail and chirping inherent to conventional gain switching in single-section lasers and is useful in direct short-pulse generation.Nanosecond laser-induced breakdown (LIB) in liquids (e.g., water) can produce dynamic high pressure and high temperature. However, since high pressure needs to negate the effect of high temperature to some degree, it is only partially effective. As a result, it is difficult to directly measure the effective pressure due to the transient and complex LIB process. Here, we presented a simple method based on Raman spectroscopy to indirectly determine the effective pressure caused by LIB in liquid pure H2O and low concentration H2O-H2O2 mixtures. By comparing the Raman shifts of the ice-VII mode for pure H2O and H2O-H2O2 mixtures under laser pumping and static high pressure, the LIB effective pressure can be first estimated. The empirical equation was then derived base on the correlation of the LIB effective pressure to ice-VII-point stimulated Raman scattering thresholds for pure and mixture water solutions, which can be used to estimate the LIB effective pressures for other different mixture water solutions with the uncertainty of 0.14-0.25 Gpa. Hopefully, our study here would advance the measurements of effective pressure in the LIB process.An 800 Gb/s/200 m free-space optical (FSO) link with a wavelength-division multiplexing (WDM)-four-level pulse amplitude modulation (PAM4) scheme and spatial light modulator (SLM)-based beam tracking technology is constructed. To the best of our knowledge, this is the first one that adopts a WDM-PAM4 scheme and an SLM-based beam tracking technology to simultaneously afford a high transmission capacity of 800 Gb/s and resolve the laser beam misalignment problem due to target device movement. By adopting a 16-wavelength WDM-PAM4 scheme, the transmission capacity of the FSO link is considerably enhanced with an 800 Gb/s (50Gb/sPAM4/λ×16λ) total capacity. check details By deploying an SLM-based beam tracking technology, the laser beam misalignment problem is practically resolved for providing an FSO link with high link accessibility. This demonstrated WDM-PAM4 FSO link fully meets the requirements of high-speed, long-reach, and high-reliability transmissions.In this Letter, a novel, to the best of our knowledge, approach to improve the imaging resolution of dark-field microscopy is proposed and demonstrated. Inspired by an existing super-resolution imaging method based on near-filed illumination using a prism or microfiber, a microparticle-generated full-direction evanescent field for sample illumination was demonstrated to achieve a multi-orientation near-field illumination in one snapshot and to obtain a super-resolution image by spatial frequency shifting. The ultimate resolution and the additional magnification factor of this method were analyzed theoretically. Imaging experiments were carried on a standard microscope calibration target MetroChip and a Blu-ray disc characterized by subwavelength microstructures. High-imaging resolution was demonstrated experimentally, and two novel illumination modes were proposed to overcome imaging direction selectivity. Our work opened up a new perspective of super-resolution imaging with near-field illumination.In this Letter, we report a polarization-entangled photon-pair source based on type-II spontaneous parametric downconversion at telecom O-band in periodically poled silica fiber (PPSF). The photon-pair source exhibits more than 130 nm (∼24THz) emission bandwidth centered at 1306.6 nm. The broad emission spectrum results in a short biphoton correlation time, and we experimentally demonstrate a Hong-Ou-Mandel interference dip with a full width of 26.6 fs at half-maximum. Owing to the low birefringence of the PPSF, the biphotons generated from type-II SPDC are polarization-entangled over the entire emission bandwidth, with a measured fidelity to a maximally entangled state greater than 95.4%. The biphoton source provides the broadest bandwidth entangled biphotons at O-band to our knowledge.A method for the agile generation of the optical frequencies required for laser cooling and atom interferometry of rubidium is demonstrated. It relies on fiber Bragg grating technology to filter the output of an electro-optic modulator and was demonstrated in an alignment-free, single-seed, frequency-doubled fiber laser system. The system was capable of frequency switching over a 30 GHz range in less than 40 ns, with ∼0.5W output power and amplitude modulation with a ∼15ns rise/fall time and an extinction ratio exceeding 80 dB. The technology is ideal for enabling high-bandwidth, mobile industrial, and space applications of quantum technologies.The time profile of a lasing signal at 391.4 nm emitted by a weakly ionized gas of nitrogen molecules at low pressure is measured under double excitation with intense femtosecond laser pulses at 800 nm. An abrupt decrease in emission occurs at the time of arrival of the second pulse. It is explained by a transfer of population from ground to first excited ionic level and by a disruption of coherence, terminating the conditions for lasing in a V-scheme without population inversion.A holographic sensor based on camphorquinon doped poly (methyl methacrylate-co-lauryl methacrylate) (poly (MMA-co-LMA)) elastic photopolymer is developed for characterizing the shear deformation of material. A shear angle and its transverse displacement, which are induced by a couple of shear stresses, are analyzed using a diffraction spectrum of a transmission holographic sensor. The dependence of the peak wavelength shift on the shear deformation presents a good linear relationship which provides a quantitative characterization means. The detectable maximum of the shear angle exceeds 26.1 deg, and the peak wavelength shift closes to 4.0 nm. The available sensitivity is better than 3.33 deg/0.5 nm (shear angle/wavelength shift) using a commercial spectrometer with 0.5 nm of resolution. Finally, the reversibility response of shear deformation further confirmed the practical applicability of the elastic polymer-based shear deformation sensor. The spectrum measurement of shear deformation provides a novel measurement means for the mechanical deformation of materials and expands the application of a holographic sensor.