ABSTRACT
Quasi-parametric chirped-pulse amplification (QPCPA), which features a theoretical peak power much higher than those obtained with Ti:sapphire laser or optical parametric chirped-pulse amplification, is promising for future ultra-intense lasers. The doped rare-earth ion used for idler dissipation is critical for effective QPCPA, but is usually not compatible with traditional crystals. Thus far, only one dissipative crystal of Sm3+-doped yttrium calcium oxyborate has been grown and applied. Here we introduce optical means to modify traditional crystals for QPCPA applications. We theoretically demonstrate two dissipation schemes by idler frequency doubling and sum-frequency generation with an additional laser. In contrast to absorption dissipation, the proposed nonlinear dissipations ensure not only high signal efficiency but also high small-signal gain. The demonstrated ability to optically modify crystals will facilitate the wide application of QPCPA.
ABSTRACT
Quasi-parametric amplification (QPA), a variant of optical parametric amplification, can release the phase-matching requirement owing to the introduction of idler dissipation, and thus may support ultrabroad bandwidth. Here we establish the gain-dispersion equation for QPA, which reveals the interplay of signal gain, idler dissipation and phase mismatch. The idler dissipation dramatically enhances the gain bandwidth, which breaks the limit set by phase matching. We theoretically demonstrate that QPA with strong dissipation allows high-efficiency few-cycle pulse amplification in those nonlinear crystals without a magic phase-matching solution.
ABSTRACT
Optical rectification (OR) is a popular way to generate coherent terahertz radiation. Here, we develop a sub-picosecond mid-infrared (mid-IR) light source with a tailored wavelength and pulse duration for enhancing the OR efficiency. Numerical simulations for a LiNbO3-based OR with tilted pulse-front excitation are first conducted to determine the optimal parameters of pump wavelength and pulse duration, demonstrating that the OR efficiency pumped by 4-µm sub-picosecond (0.5-0.6 ps) pulses is approximately twice the value with 0.8-µm pump at the same conditions. Guided by the simulation results, we build a BaGa4Se7-based optical parametric chirped-pulse amplification system with 1030-nm thin-disk pump and broadband mid-IR seeds. The output performances of >200-µJ pulse energy, â¼600-fs pulse duration and 1-kHz pulse repetition rate are achieved in a spectral range tunable from 3.5 to 5 µm. The large energy scalability and high parameter tunability make the light source attractive to high-efficiency OR in various materials.
ABSTRACT
Broadband optical parametric amplifiers (OPAs) require a group-velocity matching between the signal and the idler. For mid-infrared OPAs, however, the group-velocity matching is usually difficult to meet, rendering a limited gain bandwidth. Here, we report a serial synthesis of bandwidth-limited OPAs to provide a broad gain bandwidth. In a proof-of-principle experiment, two mid-IR OPAs based on KTA crystals with different phase-matching angles are sequentially employed to amplify different spectral regions of a broad seed pulse centered at 3.1 µm. Compared to the traditional two-stage OPA, here the gain bandwidth is nearly doubled, resulting in a much shorter compressed pulse. Such a serial synthesis approach, independent of a nonlinear crystal and an interaction wavelength, particularly suits for enlarging the gain bandwidth of OPAs when broadband amplification is impossible to achieve by a single crystal.
ABSTRACT
We propose a scheme for the direct generation of an ultrashort pulse train as well as the further compression of pulsed lasers based on the nonlinearity inherent to parity-time (PT) symmetric optical systems. Implementation of optical parametric amplification in a directional coupler of χ(2) waveguides enables ultrafast gain switching through pump-controlled breaking of PT symmetry. We theoretically demonstrate that pumping such a PT symmetric optical system with a periodically amplitude-modulated laser enables periodic gain switching, which can directly convert a continuous-wave signal laser into a train of ultrashort pulses. We further demonstrate that by engineering the PT symmetry threshold, an apodized gain switching that enables the production of ultrashort pulses without side lobes. This work suggests a new approach for exploring the non-linearity inherent to various PT symmetric optical structures to extend optical manipulation capabilities.
ABSTRACT
Full pump depletion corresponds to the upper limit of the generated signal photons relative to the pump pulse; this allows the highest peak power to be produced in a unit area of ultraintense laser amplifiers. In practical systems based on optical parametric chirped-pulse amplification, however, the typical pump depletion is only ~35%. Here, we report quasi-parametric chirped-pulse amplification (QPCPA) with a specially designed 8-cm-thick Sm:YCOB crystal that highly dissipates the idler and hence improves pump depletion. We demonstrate 56% QPCPA energy efficiency for an 810-nm signal converted from a 532-nm pump, or equivalently 85% pump depletion. As another advantage, such a record high depletion greatly suppresses the parametric superfluorescence noise in QPCPA to only ~1.5 × 10-6 relative to the amplified signal energy. These results pave the way to beyond the ten-petawatt peak power of the currently most intense lasers.
ABSTRACT
We report on a red-diode-clad-pumped continuous-wave (CW) and mode-locked Er:ZBLAN fiber laser at 3.5â µm for the first time. Numerical simulation shows that a heavily-doped Er:ZBLAN fiber is favorable for effective generation of 3.5â µm laser through 658â nm laser diode pumping. Using a 7.0â mol.% Er:ZBLAN fiber, CW output power of 203â mW was experimentally obtained at 3462â nm. By incorporating a home-made semiconductor saturable absorber mirror into the cavity, diode-pumped CW mode-locked 3.5â µm Er:ZBLAN fiber laser was first demonstrated with an average power of 19â mW, a pulse duration of 18.1 ps, and a repetition rate of 46â MHz. The research results show that red-diode-clad-pumping provides a simple and potential scheme for 3.5â µm CW and mode-locked Er:ZBLAN fiber laser.
ABSTRACT
Semiconductor saturable absorber mirrors (SESAMs) have been regarded as a revolutionary technology for ultrafast mode-locked lasers, producing numerous landmark laser breakthroughs. However, the operating wavelength of existing SESAMs is limited to less than 3â µm. In this study, we create a 3-5â µm mid-infrared (MIR) SESAM by engineering an InAs/GaSb type-II superlattice. Bandgap engineering and the strong coupling between potential wells in a superlattice enable a broadband response of saturable absorption in the 3-5â µm spectral range. Using the fabricated SESAM, we realize a SESAM mode-locked Er:ZBLAN fiber laser at 3.5â µm, which delivers MIR ultrashort pulses with high long-term stability. The breakthrough of SESAM fabrication in the MIR will promote the development of MIR ultrafast coherent sources and related application fields.
ABSTRACT
Optical parametric chirped-pulse amplification (OPCPA) is prone to undesired spatiotemporal couplings. This Letter studies a family of OPCPA couplings resulting from the nonlinear phase shift induced by frequency-dependent phase mismatch. These OPCPA couplings manifest as pulse-front deformation, transversely varying pulse duration, and spectrally varying wavefront curvature, which are directly linked with the phase-mismatch dispersion terms. The numerical study in this Letter also reveals that the focused signal intensity severely degrades with increasing signal bandwidth and pump depletion.
ABSTRACT
The existing pulsed laser technologies and devices are mainly in the infrared spectral region below 3 µm so far. However, longer-wavelength pulsed lasers operating in the deep mid-infrared region (3-20 µm) are desirable for atmosphere spectroscopy, remote sensing, laser lidar, and free-space optical communications. Currently, the lack of reliable optical switches is the main limitation for developing pulsed lasers in the deep mid-infrared region. Here, we demonstrate that topological semimetal antimonene possesses an ultrabroadband optical switch characteristic covering from 2 µm to beyond 10 µm. Especially, the topological semimetal antimonene shows a very low saturable energy fluence (only 3-15 nJ cm-2 beyond 3 µm) and an ultrafast recovery time of ps level. We also demonstrate stable Q-switching in fiber lasers at 2 and 3.5 µm by using topological semimetal antimonene as passive optical switches. Combined with the high environmental stability and easy fabrication, topological semimetal antimonene offers a promising optical switch that extends pulsed lasers into deep mid-infrared region.
ABSTRACT
Resonant cascaded nonlinearity (RCN) induced by optical parametric amplification (OPA) in a chirped quasi-phase-matching chip can be applied to control the group velocity of ultrafast lasers. However, the group delay produced in a single-stage OPA is limited to the pulse duration, and its sign cannot be altered. In this study, we propose a tandem RCN configuration with multiple OPA stages that can produce large-magnitude and sign-controllable group delays. The group delay produced in the multi-stage configuration is shown to be a linear superposition of each single-stage group delay. By virtue of the byproduct idler in the OPA process, the signal-group delay can be altered from positive to negative (and vice versa) with the same chip structure and pump condition. In the numerical simulation with two OPA stages, both a positive and negative group delay of six-fold pulse duration were achieved for 100-fs pulses at 1550 nm. A much larger group delay can be achieved by increasing the number of OPA stages.
ABSTRACT
An ultrashort mid-infrared (IR) source beyond 5 µm is crucial for a plethora of existing and emerging applications in spectroscopy, medical diagnostics, and high-field physics. Nonlinear generation of such sources from well-developed near-IR lasers, however, remains a challenge due to the limitation of mid-IR crystals. Based on oxide La3Ga5.5Nb0.5O14 (LGN) crystals, here we report the generation of femtosecond pulses tunable from 3 to 7 µm by intrapulse difference-frequency generation of 7.5 fs, 800 nm pulses. The efficiency and bandwidth dependences on pump polarization and crystal length are studied for both Type-I and Type-II phase-matching configurations. Maximum pulse energy of â¼10nJ is generated at 5.2 µm with a conversion efficiency of â¼0.14%. Because of the few-cycle pump pulse duration, the generated mid-IR pulses are as short as about three cycles. These results, to the best of our knowledge, represent the first experimental demonstration of LGN in generating mid-IR ultrashort pulses.
ABSTRACT
Mid-infrared femtosecond vortex beams generated by optical parametric oscillators (OPO) are reported for the first time, to the best of our knowledge. Order-tunable femtosecond Hermite-Gauss beams from the first to sixth order are produced from a synchronously pumped OPO and then converted into the corresponding first through sixth-order femtosecond vortex beams by a cylindrical lens mode converter. By slightly tuning the cavity length, the wavelength of the vortex beam can be continuously tunable in the range from 2323 to 2382 nm, and the pulse duration can be changeable from ${\sim}{400}\;{\rm fs}$â¼400fs to ${\sim}{1.1}\;{\rm ps}$â¼1.1ps. The work provides a flexible and reliable way to generate mid-infrared femtosecond vortex beams, and is of special significance for expanding the wavelength range of femtosecond vortex beams and their application fields.
ABSTRACT
In this Letter, we study short-wavelength conical refraction (CR) via sum-frequency generation (SFG) in the femtosecond regime, a previously unaddressed topic. Based on biaxial crystal of KGd(WO4)2 whose dispersion of optical-axis orientation is negligible in near-IR, conventional femtosecond lasers at 800 and 1054 nm are transformed into CR beams, respectively. Femtosecond CR beams at 454 nm are generated via SFG with the near-IR CR beams. While the generated sum-frequency ring is typically incomplete, a full-ring distribution can be achieved by adopting Type-II SFG with a large phase mismatch. We find that the femtosecond sum-frequency ring under various phase-matching conditions evolves as typical CR beams.
ABSTRACT
Slow and fast light are ubiquitous in optical amplifiers. In this Letter, we show for the first time, to the best of our knowledge, that optical parametric amplification (OPA) in chirped quasi-phase-matching structures can act as a platform for group-velocity control in the femtosecond regime. The resonant cascaded nonlinear phase underlies the group-velocity control, which manifests an unusual effect that both slow and fast light can be achieved under the normal condition of signal amplification. As numerically demonstrated in the OPA based on the lithium niobate crystal, the signal and idler pulse can be significantly delayed in time comparable to the signal duration and can also keep high fidelity for durations down to 100 fs until the crystal dispersion becomes effective. The broad bandwidth, large group delay, and direct compatibility with integrated optics will make the proposed platform attractive to both fundamental research and applied science.
ABSTRACT
With the proposal of dual-wavelength pumping (DWP) scheme, DWP Er:ZBLAN fiber lasers at 3.5 µm have become a fascinating area of research. However, limited by the absence of suitable saturable absorber, passively Q-switched and mode-locked fiber lasers have not been realized in this spectral region. Based on the layer-dependent bandgap and excellent photoelectric characteristics of black phosphorus (BP), BP is a promising candidate for saturable absorber near 3.5 µm. Here, we fabricated a 3.5-µm saturable absorber mirror (SAM) by transferring BP flakes onto a Au-coated mirror. With the as-prepared BP SAM, we realized Q-switching and mode-locking operations in the DWP Er:ZBLAN fiber lasers at 3.5 µm. To the best of our knowledge, it is the first time to achieve passively Q-switched and mode-locked pulses in 3.5 µm spectral region. The research results will not only promote the development of 3.5-µm pulsed fiber lasers but also open the photonics application of two-dimensional materials in this spectral region.
ABSTRACT
Frequency-domain optical parametric amplification (FOPA) is a new scheme that enables extremely broadband amplification of ultraintense pulses. The spatiotemporal coupling property of signal pulses can make the coherent noise of FOPA sharply different from that of conventional OPCPA. This paper presents a first theoretical study on the coherent noise produced in a FOPA system. We reveal that the coherent noise acquires the spatiotemporal coupling, and thus distinguishes the compressed signal pulse not only in time but also in space, which allows the suppression of coherent noise via optical manipulations in the spatial domain. The quantitative impacts of spatiotemporal coherent noise originated from the imperfections in either pump laser or crystal surfaces, are numerically studied. The result provides a new perspective on improving the coherent contrast of ultraintense lasers.
ABSTRACT
The pulse contrast of state-of-the-art petawatt lasers is limited by coherent noise. This paper reports on a new family of noise, termed nonlinear beat noise, which is generated by the nonlinear mixing of two kinds of coherent noise in optical parametric chirped-pulse amplification (OPCPA). We theoretically study the various nonlinear beat noises and reveal their intensity evolutions in an OPCPA amplifier. The results suggest that nonlinear beat noise will be destructive to the future hundred-petawatt lasers.
ABSTRACT
Quasi-parametric chirped pulse amplification (QPCPA) is a new scheme that enables the amplification of chirped signal pulses without back conversion by depleting the idler pulses. In this paper, we present a numerical study on the bandwidth, efficiency, and robustness of QPCPA. Self-locked phase among the interacting waves is found to be the underlying mechanism for the suppression of back conversion, which allows signal efficiency approaching to the quantum limit even under the phase-mismatch condition, and thus greatly increases the phase-mismatch tolerance of QPCPA. We demonstrate that QPCPA can break through the trade-off between the efficiency and bandwidth encountered in conventional optical parametric amplification, hence supporting highly efficient amplification of few-cycle pulses.
ABSTRACT
The spectroscopic characteristics, continuous-wave (CW) and mode-locking laser performances of Tm,Y:CaF2 disordered crystal were studied. A maximum CW output power of 586 mW was obtained with a slope efficiency of 26%. The Tm,Y:CaF2 mode-locked laser could operate in two states: single-wavelength mode locking or dual-wavelength synchronous mode locking. The single-wavelength mode-locked laser generated pulses with pulse duration of 22 ps, repetition rate of 99 MHz, and pulse energy of 1.15 nJ at 1887 nm. Alternatively, the laser could also be mode-locked simultaneously at 1880.7 nm and 1889.0 nm wavelengths. The beating modulation in autocorrelation trace shows that the dual-wavelength pulses were temporally synchronous.