Generated Signal Pulses Research Articles

Efficient femtosecond optical parametric generation in group-velocity-matched MgO:PPLN at 10 MHz.

We report on efficient single-pass optical parametric generation (OPG) of broadband femtosecond pulses in the mid-infrared at 10 MHz by exploiting group-velocity-matched interaction in a 42-mm-long MgO:PPLN crystal. Using a microchip-started femtosecond amplified Mamyshev oscillator at 1064 nm as the pump, the OPG source can provide tunable femtosecond pulses across 1516-1566 nm in the signal and 3318-3568 nm in the idler, with slope efficiencies of ∼93% and ∼41%, respectively. For 650 mW of average input pump power, signal powers of up to 283 mW at 1524 nm are generated, with more than 200 mW over the entire tuning range. Idler average powers of up to 104 mW at 3450 nm, with more than 80 mW across the full range, are also obtained. For input pump pulses of ∼182 fs, the generated signal pulses have a duration of ∼460 fs at 1516 nm. The idler pulses have a typical bandwidth of ≥100 nm over the entire tuning range, and as wide as 181 nm at 3457 nm. The OPG source exhibits excellent passive power stability, better than 0.5% rms in the signal and 0.6% rms in the idler, over 1 h, both in Gaussian TEM00 spatial profile with M2 < 1.5.

Tunable pulse advancement and delay by frequency-chirped stimulated Raman gain with optical nanofiber.

We demonstrate a novel method to optically tune the pulse advancement and delay based on stimulated Raman gain in hydrogen. With a frequency-chirped pump, the generated signal pulse is selectively amplified at the leading or trailing edge of the pump pulse, depending on whether the frequency difference between the pump and the signal beam is blue or red detuned from the Raman transition, which results in advancement or delay of the signal peak. Different from the method of slow/fast light, where advancement and delay are accompanied with power loss and gain, respectively, for a single resonance, both the advancement and delay are realized in the gain region for the method here. With a piece of 48-mm-long optical nanofiber in hydrogen, the time-shift for a signal peak ranging from 3.7 to -3.7 ns is achieved in a Raman-generated pulse with width of ∼12n s.

Self-Pulsed Nanosecond 2.7- &lt;named-content content-type="math" xlink:type="simple"&gt; &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$\mu\text{m}$&lt;/tex-math&gt;&lt;/inline-formula&gt;&lt;/named-content&gt; Solid-State Erbium Laser by Cooperatively Enhanced Reabsorption

The nanosecond self-pulsing operation of a midinfrared solid-state laser with no additional passive absorbers is reported in this paper. A proof-of-principle demonstration of the cooperatively enhanced reabsorption method, in which two laser-diode-pumped erbium gain media share the same laser resonator, is proposed. The two excited media act cooperatively to enhance the reabsorption effect and amplify the generated signal pulses. Under the pump power of 3.8 W, pulses with a pulse repetition rate of 6.2 kHz, an average output power of 107 mW, and a single pulsewidth of 185 ns are obtained.

Femtosecond-laser pumped CdSiP_2 optical parametric oscillator producing 100 MHz pulses centered at 62 μm

We report the first, to the best of our knowledge, femtosecond-laser-pumped optical parametric oscillator (OPO) based on the newly developed nonlinear crystal, CdSiP₂. The OPO was synchronously pumped by a mode-locked Yb:KYW/Yb:fiber master-oscillator power amplifier, providing 1.053 μm pump pulses with durations of 130 fs at a repetition rate of 100 MHz. The 0.5-mm-thick CdSiP₂ crystal was cut for a type-I noncritical interaction, providing a broad phase-matching bandwidth and ensuring excellent temporal overlap among the pump, signal, and idler pulses. The OPO generated signal pulses with a spectral coverage over 1260-1310 nm and mid-infrared idler pulses with a broad spectral coverage at 5.8-6.6 μm (6.2 THz). With a 2% output coupler (OC), the threshold pump power was 600 mW. At the maximum pump power of 1.6 W, 0.55 W was absorbed due to two-photon absorption and residual linear absorption in the CdSiP₂ crystal, 0.75 W was transmitted, and 53 mW signal power was extracted through the OC. We estimate that the generated idler power was 24 mW.

Tunable, high-energy, mid-infrared, picosecond optical parametric generator based on CdSiP_2

We report a tunable, high-energy, single-pass optical parametric generator (OPG) based on the nonlinear material, cadmium silicon phosphide, CdSiP(2). The OPG is pumped by a cavity-dumped, passively mode-locked, diode-pumped Nd:YAG oscillator, providing 25 µJ pulses in 20 ps at 5 Hz. The pump energy is further boosted by a flashlamp-pumped Nd:YAG amplifier to 2.5 mJ. The OPG is temperature tunable over 1263-1286 nm (23 nm) in the signal and 6153-6731 nm (578 nm) in the idler. Using the single-pass OPG configuration, we have generated signal pulse energy as high as 636 µJ at 1283 nm, together with idler pulse energy of 33 µJ at 6234 nm, for 2.1 mJ of input pump pulse energy. The generated signal pulses have durations of 24 ps with a FWHM spectral bandwidth of 10.4 nm at central wavelength of 1276 nm. The corresponding idler spectrum has a FWHM bandwidth of 140 nm centered at 6404 nm.

Dynamical effects of the four-wave mixing enhancement induced by constructive quantum interference**Project supported by National Natural Science Foundation of China (Grant Nos. 10774059 and 10904047), the National Basic Research Program of China (Grant No. 2006CB921103), the doctoral program foundation of institution of High Education of China (Grant No. 20060183046) and the basic research foundation of Jilin University of China (Grant

In a four-level system of ultracold 87Rb atoms, through analytical and numerical calculations we propose an efficient scheme to achieve the enhanced four-wave mixing process and demonstrate its dynamical control by various parameters such as the travel distance z, probe detuning δ and the probe pulse width τ. In particular, we find that the maximal intensity of the nonlinearly generated signal pulse can be about 80% of the initial input probe under the optimal condition. This greatly enhanced conversion efficiency occurs due to the constructive quantum interference between two different components of the generated signal pulse.

High-harmonic-repetition-rate, 1 GHz femtosecond optical parametric oscillator pumped by a 76 MHz Ti:sapphire laser

We demonstrate the generation of femtosecond pulses in a synchronously pumped optical parametric oscillator (SPOPO) at the harmonics of pump repetition rate using a SPOPO cavity longer than the fundamental synchronous length. The SPOPO is based on a 1 mm crystal of periodically poled LiNbO(3) and pumped by a Kerr-lens mode-locked Ti:sapphire laser at 76 MHz. By increasing the SPOPO synchronous cavity length we have generated output signal pulses at successive harmonics of the pump repetition rate up to the 13th harmonic at 988 MHz, where average signal powers of 30 mW are still available for 1.45 W of pump power. The generated signal pulses at 988 MHz are near transform limited with average durations of 227 fs and a time-bandwidth product of 0.41 for 185 fs input pump pulses.

Cross-phase modulation induced ultrashort pulse train generation from cw light in the normal-dispersion regime of optical fibers

A novel technique that leads to the generation of a train of ultrashort optical pulses from cw light in the wavelength regime of normal fiber dispersion is proposed. It consists of copropagating a cw signal with a train of closely spaced pump pulses in an optical fiber where both the signal and the pump experience normal fiber dispersion. As the pump broadens, the part of the signal between neighboring pump pulses becomes negatively chirped owing to pump pulse collision induced cross-phase modulation. Normal group-velocity dispersion then starts to squeeze the signal energy in the negatively chirped region, thus leading to amplitude modulation of the signal and eventually to a pulsed structure. Numerical simulations show that the generated signal pulses can be much shorter than the pump pulses.

Nanosecond optical parametric oscillator based on large-aperture periodically poled RbTiOAsO_4

We report on optical parametric oscillators (OPO's) based on periodically poled RbTiOAsO(4) (PP RTA), which are pumped by Q -switched solid-state lasers. With a diode-pumped Nd:YVO(4) laser (pulse energy, 800microJ ; pulse duration, 5.5 ns; repetition rate, 1 kHz) the PP RTA OPO generated 1.58-microm signal and 3.26-microm idler radiation with a signal pulse energy of 45microJ . The large aperture of 3 mmx3 mm of the PP RTA crystal also permitted OPO operation with pump pulse energies as high as 65 mJ, provided by a flash-lamp-pumped Q -switched Nd:YAG laser (pulse duration, 20 ns; repetition rate, 10 Hz). With this pump source the OPO generated signal pulse energies as high as 17 mJ, corresponding to an efficiency of 26%. The performance of this OPO shows that large-aperture PP RTA crystals are well suited for pulsed nanosecond OPO operation with pump pulse energies of tens of millijoules.

Generation of a Train of Ultrashort Pulses from cw Light using Cross-phase Modulation and Raman Amplification in Optical Fibers

A novel method that can lead to generation of a train of ultrashort optical pulses from cw light in the anomalous-dispersion regime of single-mode fibers is proposed. It consists of copropagating a CW signal with a train of intense pump pulses in an optical fiber whose minimum-dispersion wavelength is chosen such that it falls between the pump and the signal wavelength. The pump pulses impose nearly linear frequency chirps on the signal through cross-phase modulation and at the same time amplify the signal through stimulated Raman scattering, which induce the cw signal to evolve into a train of ultrashort pulses. Numerical simulations show that the generated signal pulses are nearly chirp free and pedestal free and are much shorter than the pump pulses. The higher the pump power is, the narrower and more intense the generated signal pulse is, and a shorter fiber is used. Finally, it is shown that the method remains applicable even for a small walk-off between the pump and the signal pulses.