Sub-100 ps monolithic diamond Raman laser emitting at 573 nm

We report a compact and efficient picosecond diamond Raman laser at 573 nm wavelength. The laser consists of a 0.5 mm thick single-crystal synthetic diamond coated to form a plane–plane laser resonator, and pumped at 532 nm by a frequency-doubled Q-switched microchip laser system. The pump delivers 85 ps pulses at 100 kHz repetition rate at a maximum average power of ~500 mW. We demonstrate 1st Stokes emission from the diamond Raman laser with maximum power of 175 mW, corresponding to a conversion efficiency of 47% and a pulse duration of 71 ps. Substantial pulse shortening is obtained by proper adjustment of the pump spot diameter on the diamond sample. A minimum pulse duration of 39 ps is reported for a conversion efficiency of 36% and 150 mW output power. The simplicity of the architecture makes the system highly appealing as a yellow picosecond laser source

9 W average power, 150 kHz repetition rate diamond Raman laser at 1519 nm, pumped by a Yb fibre amplifier

Commercially available pulsed fibre lasers at ~1.5 μm have many uses in imaging, defense, communications and light radar (LIDAR) [1]. For 3D scanning LIDAR, higher signal-to-noise ratio requires lasers with high average power and high pulse repetition rate (ideally several MHz) for faster scanning rate, whereas to improve distance resolution requires pulse durations <10 ns [2,3]. One limitation of the pulsed fibre lasers at ~1.5 μm is scaling to high average powers [4]. Raman frequency conversion of high average power fibre master oscillator power amplifier (MOPA) systems at ~1 μm is a potential alternative. The large Raman shift and Raman gain of diamond allows two-stage Raman conversion to ~1.5 μm for ~1 μm pumping [5]. Excellent thermal properties make diamond suitable for high average powers [6]. Much work has been done on conversion of 1.064 μm lasers to 1.485 μm using diamond [7]; however, the “eye-safety” requirements for LIDAR typically call for wavelengths above 1.5 μm, due to the order of magnitude higher Maximum Permissible Exposure limit [8]. Developing such a diamond Raman laser (DRL) was the major motivation for this research

Time-Resolved raman spectrometer with high fluorescence rejection based on a CMOS SPAD line sensor and a 573-nm pulsed laser

Abstract A time-resolved Raman spectrometer is demonstrated based on a 256 × 8 single-photon avalanche diodes fabricated in CMOS technology (CMOS SPAD) line sensor and a 573-nm fiber-coupled diamond Raman laser delivering pulses with duration below 100-ps full-width at half-maximum (FWHM). The collected backscattered light from the sample is dispersed on the line sensor using a custom volume holographic grating having 1800 lines/mm. Efficient fluorescence rejection in the Raman measurements is achieved due to a combination of time gating on sub-100-ps time scale and a 573-nm excitation wavelength. To demonstrate the performance of the spectrometer, fluorescent oil samples were measured. For organic sesame seed oil having a continuous wave (CW) mode fluorescence-to-Raman ratio of 10.5 and a fluorescence lifetime of 2.7 ns, a signal-to-distortion value of 76.2 was achieved. For roasted sesame seed oil having a CW mode fluorescence-to-Raman ratio of 82 and a fluorescence lifetime of 2.2 ns, a signal-to-distortion value of 28.2 was achieved. In both cases, the fluorescence-to-Raman ratio was reduced by a factor of 24—25 owing to time gating. For organic oil, spectral distortion was dominated by dark counts, while for the more fluorescent roasted oil, the main source of spectral distortion was timing skew of the sensor. With the presented postprocessing techniques, the level of distortion could be reduced by 88%-89% for both samples. Compared with common 532-nm excitation, approximately 73% lower fluorescence-to-Raman ratio was observed for 573-nm excitation when analyzing the organic sesame seed oil