Nanosecond Pulse Shaping Research Articles

Shaping of nanosecond pulses in ytterbium fiber lasers by synchronous sine-wave pump modulation

In this work, we discovered the possibility of greatly relaxing requirements to the speed and dynamic range of pump power variation and, thus, of reducing synchronous pumping of ytterbium (Yb)-based fiber lasers to a very simple pump modulation yielding a mode-locked pulsed output. We show that even slow (microsecond-scale) low-index ( ≤ 0.5 ) sine-wave synchronous modulation of the pump power can result in shaping of a regular train of nanosecond laser pulses. It is revealed that the energy-conservative process of laser pulse shortening against the pump modulation period can take place in the quasi–two-level laser active medium owing to mistiming-induced gain discrimination of the temporal laser pulse profile. Thus, nanosecond pulses with energy up to 50 nJ were obtained in our experimental all-fiber Yb-based laser configuration. Our theoretical modeling reveals routes to much stronger pulse shortening through tunable pump modulation parameters. This discovery allows the establishment of more reliable and easy-to-implement high-efficiency alternatives to other types of high-energy ultralong mode-locked fiber lasers.

Software-defined microwave photonic filter with high reconfigurable resolution.

Microwave photonic filters (MPFs) are of great interest in radio frequency systems since they provide prominent flexibility on microwave signal processing. Although filter reconfigurability and tunability have been demonstrated repeatedly, it is still difficult to control the filter shape with very high precision. Thus the MPF application is basically limited to signal selection. Here we present a polarization-insensitive single-passband arbitrary-shaped MPF with ~GHz bandwidth based on stimulated Brillouin scattering (SBS) in optical fibre. For the first time the filter shape, bandwidth and central frequency can all be precisely defined by software with ~MHz resolution. The unprecedented multi-dimensional filter flexibility offers new possibilities to process microwave signals directly in optical domain with high precision thus enhancing the MPF functionality. Nanosecond pulse shaping by implementing precisely defined filters is demonstrated to prove the filter superiority and practicability.

Nanosecond pulse shaping at 780 nm with fiber-based electro-optical modulators and a double-pass tapered amplifier.

We describe a system for generating frequency-chirped and amplitude-shaped pulses on time scales from sub-nanosecond to ten nanoseconds. The system starts with cw diode-laser light at 780 nm and utilizes fiber-based electro-optical phase and intensity modulators, driven by an arbitrary waveform generator, to generate the shaped pulses. These pulses are subsequently amplified to several hundred mW with a tapered amplifier in a delayed double-pass configuration. Frequency chirps up to 5 GHz in 2 ns and pulse widths as short as 0.15 ns have been realized.

Enhancement of ultracold molecule formation by local control in the nanosecond regime

We describe quantum simulations of ultracold 87Rb2 molecule formation using photoassociation (PA) with nanosecond-time-scale pulses of frequency chirped light. In particular, we compare the case of a linear chirp to one where the frequency evolution is optimized by local control (LC) of the phase, and find that LC can provide a significant enhancement. The resulting optimal frequency evolution corresponds to a rapid jump from the PA absorption resonance to a downward transition to a bound level of the lowest triplet state. We also consider the case of two frequencies and investigate interference effects. The assumed chirp parameters should be achievable with nanosecond pulse shaping techniques and are predicted to provide a significant enhancement over recent experiments with linear chirps.

Spectral broadening and shaping of nanosecond pulses: toward shaping of single photons from quantum emitters.

We experimentally demonstrate spectral broadening and shaping of exponentially-decaying nanosecond pulses via nonlinear mixing with a phase-modulated pump in a periodically poled lithium niobate (PPLN) waveguide. 1550 nm pump light is imprinted with a temporal phase and used to upconvert a weak 980 nm pulse to 600 nm while simultaneously broadening the spectrum to that of a Lorentzian pulse up to 10 times shorter. While the current experimental demonstration is for spectral shaping, we also provide a numerical study showing the feasibility of subsequent spectral phase correction to achieve temporal compression and reshaping of a 1 ns mono-exponentially decaying pulse to a 250 ps Lorentzian, which would constitute a complete spectrotemporal waveform shaping protocol. This method, which uses quantum frequency conversion in PPLN with >100:1 signal-to-noise ratio, is compatible with single photon states of light.

Characterization of a Linear Photoconductive Switch Used in Nanosecond Pulsed Electric Field Generator

In this letter, an experimental and quantitative study on the resistance behavior of a photoconductive semiconductor switch (PCSS) is reported. The study of the PCSS behavior is important for an accurate integration in a nanosecond pulse shaping generator. The effect of the bias voltage and the optical pulse energy on the switching efficiency is presented. The shift of the PCSS absorption threshold under the bias voltage is also described. The minimum resistance reached by the silicon semiconductor during the temporal switching is 3.8 Ω for 4-kV bias voltage and 48-μJ optical energy.

Nanosecond Pulse Shaping of a Flashlamp-Pumped Dye Laser

Many studies of molecular processes have utilized flashlamp-pumped dye lasers as a source of wavelength tunable, moderate energy (1 mJ) microsecond optical pulses. The chief attribute of such devices is the ability to generate a high concentration of excited states. Unfortunately, the temporal width of the output limits most investigations to relatively slow events. This drawback could be circumvented by shortening the pulses using any of several schemes. However, most of the commercially available approaches, such as pulse slicing or Q-switching, suffer from inflexible pulse shaping or the inability to conserve and deliver the original laser energy. On the other hand, it has been shown that cavity-dumping can be used with a CW dye laser to both store the radiation and then deliver it in a variety of optical waveforms ranging from sawtooth to Gaussian shapes. In this note we wish to report the construction of a cavity-dumped flashlamp-pumped dye laser that is capable of generating a varied temporal output either of trains or single pulses with energies from 0.1 to 0.5 mJ.