Narrow linewidth pulsed single-frequency fiber laser has the characteristics of excellent coherence and high peak power, and has been widely used in coherent LiDAR, precision measurement and nonlinear frequency conversion. In this work, energy scaling of single-frequency laser with long pulse duration and low repetition rate is demonstrated through leveraging an all-fiber amplifier based on polarization-maintaining (PM) large mode area tapered Yb-doped fiber. With dedicate synchronous pulse pumping for suppressing the inter-pulse ASE effect, and pre-shaping of the seed pulse for compensating the distortion of temporal profile, a 1064nm pulsed single-frequency laser output with an energy of 370mJ is realized with a repetition rate of 100Hz. In addition, the rectangle pulse shape is well maintained with a duration of 1.1ms. It is believed that the obtained result represents the highest energy ever reported for pulsed single-frequency fiber lasers.
A high-power linearly-polarized all-fiber single-frequency amplifier at 1064 nm based on tandem corepumping is demonstrated by adopting large-mode-area (LMA) fiber with core/cladding diameter of 20/130 μm. The output performance of the amplifier dependence on the input signal power has been investigated, and the results indicate that enhancing the injection signal power is advantageous in mitigating the amplified simultaneous emission (ASE) and increasing slope efficiency. A maximum output power of 252 W with corresponding slope efficiency of 85% is achieved with injection signal power of 7 W. At the highest output power status, a polarization extinction ratio (PER) of 17 dB and a beam quality of 1.15 are obtained respectively. In addition, by virtue of LMA fiber and tandem core-pumping, the amplifier exhibits good performance on thermal load, which in turn facilitate the maintenance of frequency noise and linewidth. To the best of our knowledge, this is the highest output power of single-frequency all-fiber amplifier based on core-pumping scheme.
An all-fiber high-power Mamyshev oscillator (MO) with only one amplification stage was experimentally demonstrated. The achieved maximum output power was 3.4 W with 77 nJ pulse energy and could be compressed to ~100 fs. By adjusting the pump power, the phenomenon of harmonic mode locking is observed in the experiment, and the highest 5th order harmonic can be achieved, which corresponds to the repetition rate of 44.1 MHz. This compact MO ultrafast laser could operate stably several hours and the power fluctuation within 5 h was less than 0.12%. Such a high power ultrafast laser oscillator could apply a promising source for advanced fabrication, biomedical imaging, micromachining and other practical applications.
An all fiber-based Mamyshev oscillators (MO) is experimentally demonstrated to achieve high energy pulse output. In this high energy MO system, the maximum single pulse energy of 153 nJ was achieved with 1.5 W average power. The pulse width could be externally compressed to < 100 fs by a pair of diffraction gratings. Considering the insertion loss of gratings, the maximum peak power was >1 MW. Meanwhile, this system is verified to have good long-term stability and can run several hours stably. This is the highest record in pulse energy from the all fiber-based ultrafast laser oscillator with picosecond/femtosecond pulse duration, to the best of our knowledge. Such a high energy oscillator could apply a promising source for laser micromachining, advanced fabrication, biomedical imaging, and other practical applications.
A gain-managed nonlinear (GMN) tapered fiber amplifier was experimentally demonstrated. The achieved single pulse energy was 707 nJ and the compressed pulse duration was 67 fs with 10 MW peak power at 1054 nm central wavelength.
A single-polarization single-frequency (SPSF) 1030 nm distributed feedback (DFB) fiber laser with mode switchable output is achieved. The DFB fiber laser is realized based on a 5 cm long π-phase shifted fiber Bragg grating (PS-FBG). A maximum output power of 84 mW with single-polarization operation is achieved. The polarization extinction ratio (PER) is around 17 dB and the linewidth is 18 kHz. The slope efficiency is 13% and the spectrum at the highest power shows an excellent optical signal to noise ratio of about 75 dB. Moreover, LP11 mode single-frequency lasing is achieved by adopting an acoustically-induced fiber grating (AIFG). The mode purity is estimated to be higher than 96%. These results, to the best of our knowledge, show the highest output power among the reports that achieve single-frequency 1030 nm DFB laser output with single-polarization operation. Furthermore, it is the first time to realize transverse mode switchable single-frequency fiber laser based on an AIFG. The high order mode single-frequency 1030 nm fiber laser has much potential to find applications in multiplexing system.
Single-pixel imaging (SPI) uses single-pixel detectors to detect two-dimensional images, breaking through the limitations of traditional imaging methods on imaging dimensions and resolution. SPI can achieve large-bandwidth signal responses from near-ultraviolet to far-infrared and even terahertz bands, which provides a solution to the imaging needs of some complex environmental conditions. However, SPI sacrifices imaging time in exchange for spatial resolution limits its application and development. In order to increase the imaging speed and improve the imaging quality, this paper proposes a new ordering of the Hadamard basis, which can restore image information with high quality in low sampling regime. Simulation verifies that 64 x 64 pixels image can be completely reconstructed at a sampling rate of 12.5%. A single-pixel imaging experiment based on time-correlated single photon counting techniques (TCSPC) was designed to record the reflection and total reflection phenomenon of light propagating in water, 64 x 64 pixels image could be reconstructed well under 12.5% sampling rate.
We present a symmetrically semi-spiral phase plate (SSSPP), which possesses a continuous and closed surface, for converting a linear polarization light into radial polarization light. By technique of ultra-precision free-form surface machining, it is possible to achieve a convertor with large aperture and high damage threshold. This kind of SSSPPs, firstly fabricated using MgF2 and CaF2 with Φ50mm by single point diamond turning, is demonstrated and measured in an experiment. Additionally, the available materials also include KDP, LiNbO3, some plastic material and glasses, etc.
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