Superconducting nanowire single photon detector response to X-ray photon was demonstrated using a laser-plasma subps X-ray radiation, to the best of our knowledge. The time jitter was measured to be 248.2 ps, which is larger than ordinary visible or NIR SNSPDs and its efficiency is relatively lower, but the results pave the way for a new competitive X-ray detector with ultrahigh count rates, ultralow timing jitter, ultrahigh sensitivity and negligible dark counts.
Multi-photon microscopy (MPM) has become an indispensable tool for observing biological structures and functions in vivo, benefitting from its deep penetration depth and high spatial resolution. Femtosecond pulses featuring a broad wavelength tuning range are highly desired by MPM. We demonstrate a 1-MHz ultrafast fiber-optic source that produces ~100-fs pulses tunable from 940 nm to 1250 nm with 100-nJ level pulse energy. For example, we achieved 120-fs pulses with 105-nJ energy centered at 1150 nm. This broadly tunable, energetic fs source constitutes an ideal source for deep-tissue multi-photon imaging.
Mixed molybdenum tungsten disulphide (MoxW1-xS2), a new member of the transition metal dichalcogenides, has drawn much research attention in the photonic devices. In this work, we demonstrate a Q-switched Tm-doped fiber laser (TDF) using Mo0.8W0.2S2 polymer film as a saturable absorber (SA). Mo0.8W0.2S2 is obtained by microwave-assisted solvothermal method and its nanosheets are embedded into a polyvinyl alcohol (PVA) film. The film SA is sandwiched between two fiber connectors and is inserted into the all-fiber TDF laser cavity. The total cavity length of TDF is 30m and a 4 m Tmdoped fiber is used as the gain medium. The TDF is pumped by a multimode 793nm laser diode (LD). Use the polarization controller (PC) to change the polarization states, a relatively stable Q-switched pulse train are realized when the pump power up to 2.17 W. The output power of the oscillator increase from 4.4 mW to 7.3 mW with the pulse repetition rate from 11.9 kHz to 15.7 kHz. In addition, the shortest pulse duration of 11.7 μs generated with the pump power of 2.26W.
We will report the new experimental results on MID femtosecond laser based on a multi-stage optical parametric amplifier, a new nonlinear crystal, SiC, was used for the three waves interaction. Comparative research with KTA crystal were also carried out. With optimized conditions, laser energy up to 520 μJ was obtained with central wavelength of 2.8 μm at 1kHz repetition rate. In this experiment, a home-made femtosecond Ti:sapphire laser system was used as pump laser. The seeding signal was introduced from the 3-mm YAG plate based white continuum and then pre-amplified in three non-collinear amplification stages. With 10-mJ pump energy in the last stage amplifier, laser energy up to 1.8 mJ for signal wave and 520 μJ for idler wave were obtained. Corresponding to a total conversion efficiency of 23.2% (signal plus idler). To maximize the bandwidth of the idler, a numerical model was developed to give an optimum non-collinear angle. As the result, the bandwidth as wide as 525 nm was realized, supporting 27 fs transform-limited pulse generation.
A practical femtosecond polarization-maintaining Yb-doped fiber amplifier enabling 153 fs transform-limited pulse duration with 32 μJ pulse energy at 1 MHz repetition rate corresponding to a peak power of 0.21 GW is demonstrated. The laser system based on chirped-pulse amplification (CPA) technique is seeded by a dispersion managed, nonlinear polarization evolution (NPE) mode-locked oscillator with spectrum bandwidth of 31 nm at 1040 nm and amplified by three fiber pre-amplifying stages and a rod type fiber main amplifying stage. The laser works with beam quality of M2 of 1.3 and power stability of ∼0.63% (root mean square, RMS) over 24 hours will be stable sources for industrial micromachining, medical therapy and scientific research.
Carrier-enveloped phase controlled femtosecond laser has an important application in the absolute frequency
measurement, which lead to a revolutionary progress in the frequency metrology. In this paper we will report a high
stable optical frequency comb based on a 90MHz repetition rate Ti:sapphire laser, by using a photonic crystal fiber to
broaden octave spanning spectrum and a self-reference technology to measure the offset frequency fceo, both the
repetition rate frep and fceo are locked simultaneously to a cesium clock with phase lock loop (PLL) technology. For
simultaneous stabilization of frep and fceo, two sets of phase-locked loop electronics are introduced to control separately the
laser cavity length for frep with a PZT and the pump laser for fceo with an acoustic optics modulation (AOM) respectively.
As the result, we stabilized the frep at a fluctuation within the order of μHz, and fceo is in the order of mHz, which support
a frequency comb with an uncertainty of 10-14.
We report a self-starting mode-locked Cr:forsterite laser with 1030 nm Yb:YAG laser as the pump laser in this paper. Two chirped mirrors are used to provide the negative intracavity group-delay dispersion; the mode locking is initiated and stabilized by a semiconductor saturable-absorber mirror (SESAM). With absorbed power of 7W at 1030nm, stable femosecond laser pulses with average power of 202 mW were obtained at a repetition rate of 82.6 MHz, the autocorrelation measurement shows the typical pulse duration is about 29 fs.
A white light continuum of octave spanning was produced by self-phase modulation in a hollow-core fiber filled with
noble gases at high pressure and subsequently compressed by a set of ultra-broadband chirped mirrors. Pulses as short as
5.1 fs with energy up to 400 μJ at a 1 kHz repetition rate were obtained. Based on the carrier-envelope phase (CEP)
locking of the femtosecond oscillator and the spectral interference of the white light continuum between the white
fundamental wave and the harmonic wave at the same wavelength, the CEP of 5.1 fs pulse can be further locked by
modulating the pump laser through a slow loop. The intense, few-cycle laser pulses with a stable CEP will enable us to
produce high-order harmonic X-ray laser by the interaction with a rare gas target, this may drive the individual
attosecond pulse generation.
An ultrabroaden spectrum covered from 600nm to 1000nm was directly generated from a self-designed femtosecond
laser. The laser resonator consists in only three or four chirped mirrors and one output coupler, we measured the pulse
duration is shorter than 7fs by compensating the dispersion outside the laser cavity, repetition rate of high as 160MHz
was realized. As our best knowledge, this is the simplest laser configuration of generating the pulse of shorter than 10fs.
To control the carrier-enveloped phase (CEP), we further used a PPLN crystal to generate the difference-frequency based
on the ultrabroaden spectrum, a beat frequency with signal to noise ratio of 34dB was observed. Locking the beat
frequency and the 160MHz repetiton rate to a Cs clock, it will enable us to realize a compact frequency comb with high
repetition rate.
A self-starting all-solid-state picosecond (ps) laser was demonstrated. Different with a standard cavity design with
semiconductor saturable-absorber mirror (SESAM), self-starting mode-locking was initiated by stretching the length of
arm to reduce the beam spot, which shows the output beam possess higher beam quality than standard one. With a 10%
output coupler, we achieved 1 W output power and 21 ps pulse duration at pump power of 4.5 W. High efficiency and
high beam quality show the merit of the ps-laser.
We report the experimental research on the measurement and controlling of carrier envelope phase offset (CEO) with a home-made femtosecond Ti:sapphire laser, the beat frequency with a signal to noise ratio of as high as 45 dB is obtained with standard self-referencing technique. Locking the beat signal to the TV-Rb frequency standard by a phase-locked loop electronic circuit, a simple compact frequency comb was established. To further control the CEO with the technology of differenced frequency generation, we develop an ultra-broadened bandwidth femtosecond Ti:sapphire laser by balancing the dispersion with chirped mirrors, spectrum of covering from 600 nm to 1050 nm was observed. It will enable us to measure and control the CEO without photonic crystal fiber.
We have constructed two kinds of table-top femtosecond terawatt (TW) Ti:sapphire laser systems based on the chirped-pulse
amplification (CPA). With a compact design using only two-stage amplifiers, output energies of 36mJ and 640mJ at 10hz
repetition rates were obtained with recompressed pulse duration of 25 fs, and 31 fs respectively, corresponding to peak
powers of about 1.4 TW and 20 TW. The total pump energy for the last stage is 260 mJ and 2.8 J at wavelength of 532 nm.
These results represent a significant efficiency in amplification and a compact configuration in size. By using an adaptive
optical system to correct the wave-front distortion of the 20TW laser. we further demonstrated the improvement of beam
quality br higher focusable laser intensity.
Two independent femtosecond Ti:sapphire lasers are synchronized by using a new passive synchronization design. By
enhancing the intracavity cross-phase modulation (XPM), stable synchronization operation of remaining for more than 24
hours with a timing jitter of 0.4fs was demonstrated; the tolerance of cavity length mismatch is larger than 10 micrometers.
Effects of laser polarization were studied on behaviors of fast electrons produced from an aluminum target irradiated by obliquely incident laser pulses at 8x1015 W/cm2. Jet emission of outgoing fast electrons collimated in the polarization direction was observed for the s-polarized laser irradiation, whereas for the p-polarized irradiation, very directional emission of outgoing fast electrons was found close to the normal direction of the target. The behaviors of in-going fast electrons into the target for s- and p-polarized irradiation were also investigated by observing x-ray Bremsstrahlung radiation at the backside of the target.
The behaviors of hot electrons in femtosecond laser-plasma interaction have been studied systematically under laser irradiance of 5 X 1015 Wcm-2micrometers 2. A very directional jet emission of hot electrons with energies above 170 keV has been observed in the normal direction to the target surface. The angular distribution of the jet emission of hot electrons has been found to be dependent on the energy of hot electrons. By measuring the Faraday rotation angle of the backscattered emission, a magnetic field in the axial direction has been detected for the first time. The maximum value of the magnetic field was estimated to be as high as 1.76 +/- 0.7 Mgauss at such a modest irradiance. It is believed that this axial magnetic field is generated by the dynamo effect in the laser-plasma interaction.
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