The mode-locked fluoride fiber laser (MLFFL) is an exciting platform for directly generating ultrashort pulses in the mid-infrared (mid-IR). However, owing to difficulty in managing the dispersion in fluoride fiber lasers, MLFFLs are restricted to the soliton regime, hindering pulse-energy scaling. We overcame the problem of dispersion management by utilizing the huge normal dispersion generated near the absorption edge of an infrared-bandgap semiconductor and promoted MLFFL from soliton to breathing-pulse mode-locking. In the breathing-pulse regime, the accumulated nonlinear phase shift can be significantly reduced in the cavity, and the pulse-energy-limitation effect is mitigated. The breathing-pulse MLFFL directly produced a pulse energy of 9.3 nJ and pulse duration of 215 fs, with a record peak power of 43.3 kW at 2.8 μm. Our work paves the way for the pulse-energy and peak-power scaling of mid-IR fluoride fiber lasers, enabling a wide range of applications.
Large size of YCa4O(BO3)3(YCOB) crystals were grown both by Czochralski and Bridgman methods. Large size elements as large as 60 mm clear aperture were cut and polished with surface flatness of 1/5 wavelength. Optical
homogeneity of YCOB crystal was found in the order of 10-6. Laser damage thresholds of several YCOB crystal
elements were tested using different laser facilities with different pulse widths or wavelengths, with thresholds varied
from 0.8 GW/cm2 to more than 1 TW/cm2. One SHG and two optical parametric chirped-pulse amplification (OPCPA)
experiments were executed to characterize the nonlinear optical properties of YCOB crystals and the quality of the
crystals. The results shown that YCOB had good performance in OPCPA application, especially with low content of
parameter florescence. Combined with good NLO performance and possibility to grow large size crystals, YCOB crystal
was a good choice for high power OPCPA applications.
We report experimental results of wavelength dynamics in a soliton fiber ring laser passively mode locked by using the
nonlinear polarization rotation technique. We find central wavelength of pulses can be tuned by adjusting the
polarization controllers due to the fiber birefringence dependence on the light wavelength. The spectrum of pulses
generated from that of continuous waves (CW) is also studied. We find the wavelength shifted between the CW and the
mode-locked state exhibits hysteresis effect. The mechanism is investigated and it is found the wavelength tuning
hysteresis is the combined effects of fiber birefringence and cavity propagation property.
We have built a three-stage Ti:sapphire laser system at CAEP which could deliver 5-TW, 30-TW and 286-TW pulses to the corresponding target chambers for diverse applications with innovative high-power Ti:sapphire crystal amplifiers. Pulse durations of 30fs have been obtained by installing an acousto-optic programmable dispersive filter (AOPDF) before the stretcher to compensate for the spectral gain narrowing. By taking a number of advanced measures for spatial beam control, near-diffraction limited focal spots (FWHM) have been obtained which, to our knowledge, are the best far fields ever measured for the existing high-power Ti:sapphire laser systems without deformable mirror correction. Focused laser intensity is about 1021W/cm2 measured with an f/1.7 OAP. The laser system has the potential to operate at 500TW and even higher and laser intensities of 1022W/cm2 are expected with deformable mirror for wavefront correction and small f-number fine OAP for tighter focus added to the system in the near future.
We overview our recent progress on developing nonlinear quadratic technologies for femtosecond lasers at 1 μmicron. Quadratic optical nonlinearity χ(2) can be exploited in femtosecond lasers and regarded as a significant new degree of freedom for the design of short-pulse sources.
In this paper we find the spectral bandwidth is more important than the duration of pulse for analyzing the evolution of ultrashort laser pulses. A general novel (3+1) dimensional propagation equation first-order in the propagation coordinate is derived, which is independent of the envelope and carrier frequency. This equation provide an accurate description of the evolution of the ultrashort pulsed beam through the dispersive nonlinear medium, with the numerical value of the bandwidth being bigger than the carrier frequency and considering the true frequency. A family of exact solutions of the novel linear (3+1) dimensional equation in the dispersive medium has been derived, which represents the pulse with ultrawide bandwidth evolving due to gain (losses), dispersion, and diffraction. The use of the novel dispersive and loss coefficients is analyzed.
We report on the theoretical investigation of the amplification of highly chirped pulse with ultrabroad bandwidth. Based on the analysis of the properties of the pulse with a very big chirp, we build a theoretical model for the amplification of highly chirped pulse. The model includes the effects of homogeneous and inhomogeneous broadening. Based on our model, the difference
between the inhomogeneously and homogeneously broadening amplification is identified by numerical simulations. We believe that the obtained model can be used to evaluate the laser-performance, and optimize the laser design.
In this paper a method for obtaining a high-power ultrashort pulse
with ultrabroad bandwidth has been investigated. A theoretical
investigation of the propagation and supercontinuum generation of
the highly chirped pulse having been stretched and amplified are
presented by numerical simulations in microstructured optical
fiber. Comparing with the case of a chirp-free pulse, a chirped
pulse with the same peak power and initial bandwidth can produce a
broader supercontinuum spectrum with higher average power. After a
felicitous compression, a high power ultrashort pulse that has an
ultrabroad bandwidth much larger than that of the pump pulse can
be produced.
We present a conceptual design of multi-PW ultrashort laser system based on existing large-aperture Nd:glass laser facility. Compared with current PW laser, innovative technologies are adopted in the design, which includes large-aperture OPA to generate 10mJ femtosecond laser at 1 μmicron directly, high energy OPCPA preamplifier up to 1 J-level and chirped pulse shaping by AOPDF. To simulate the multi-PW CPA precisely, we build up an amplification model that can treat either homogenous broadening or inhomogenous gain media. As a first phase of our multi-PW laser, we are now constructing an ultrashort laser system that can produce pulse energy > 100 J with pulse duration of 350 fs.
We propose and demonstrate a simple approach to lower the thermal quenching effect and improve the output power for Cr:LiSAF lasers, which is accomplished by employing two laser rods in a combined cavity. The resonator contains two laser rods and is designed by using two “X” folding cavities in cascade. CW laser output of ~ 230 mW has been achieved with pump of single-striped laser diodes. Compared with lasers with single gain rod, the laser with dual rods shows less severe thermal effect and increases the output by more than two times.
Thin films of beta barium borate (β-BBO) have been prepared by liquid phase epitaxy on Sr2+-doped α-BBO (001) substrates. The thin films were characterized by X-ray diffraction and X-ray rocking curve. The results of X-ray diffraction indicate that the films show highly (00l) preferred orientation on (001)-oriented substrates. The full width at half-maximum of the rocking curve for the film is as low as 676.6 arcsec, which shows the high crystallinity of the thin film. The absorption edge of β-BBO on Sr2+-doped α-BBO substrate is 190 nm. The films show second harmonic generation of 400 nm light upon irradiation with 800 nm Ti: Sapphire femtosecond laser light. These results reveal the possibility of fabricating β-BBO (001) films on (001)-oriented Sr2+-doped α-BBO substrates by LPE.
In this paper we report on the design and performance of the large KDP crystal plates that were constructed to convert 1.054 micrometer laser beam to its third harmonic. The KDP crystals were AR-coated by sol-gel films. Type II/type II phase-matching configurations for cascade frequency doubling and tripling have been implemented at 250 mm aperture. High conversion efficiencies approaching to 70% were achieved. Focusing properties of harmonic beam are also investigated in the paper. Based on the transfer of electric-field amplitude and phase ripple in frequency tripling, simple formulas are derived for the harmonic laser beam-quality factor, M3(omega )2, with an arbitrary fundamental beam incident to ideal nonlinear crystals. Harmonic beam-quality is generally degraded, while the beam divergence is similar to that of the fundamental after a nonlinear frequency-conversion process. For practical crystals with periodic surface ripples due to their machining, a multi-order diffractive model is presented to study the focusing properties of harmonic beam. Predictions of the theories are shown to be in excellent agreement with full numerical simulations of tripling.
KEYWORDS: Optical amplifiers, Energy efficiency, Lamps, High power lasers, Laser welding, Glasses, Spatial filters, Optical switching, Laser energy, Energy transfer
We have constructed coaxial double-pass amplifiers with individual beamlet aperture of 20 cm in a 2 X 2 array architecture. Each element contains six phosphate glass disks. The amplifier consists of two pairs of disk amplifiers, each six deep, that share a common central flash-lamp array. The central array is expected to be more efficient for the pumping of disks, thereby raising the amplifier storage efficiency. A particular coaxial double- pass amplification optical scheme was designed. The input and output beam are performed by spatial filter. Technique advantage is avoidance of large aperture electric optical switch. In this paper we theoretically calculate population inversion variation in multipass amplification and the gain of multipass amplification. The experimental results are in agreement with the theoretical calculation.
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