Mahendra Man Shakya

Achieving 280fs resolution with a streak camera by reducing the deflection dispersion

The factors that limit the temporal resolution in a streak camera operating in an accumulative mode were studied. By controlling the timing jitter, the transit-time dispersion and the technical resolution of the camera on the order of 100fs, the role of the deflection dispersion was investigated experimentally. It was done by changing the electron beam size in the deflection plates with a variable slit in front of the plates. The temporal resolution of the camera reached 280fs when the slit width was a 5μm slit.

A low-loss, robust setup for double optical gating of high harmonic generation

Previously, a second harmonic field was added to a polarization gating field by a Mach–Zehnder interferometer to gate the high harmonic generation process in argon gas. To reduce the losses of the interferometer, we developed a collinear setup consisting of only two quartz plates and a barium borate crystal. The high intensity at the focus allowed the double optical gating to be performed on neon gas. As a result, a supercontinuous spectrum was produced capable of supporting 130as. There is no delay jitter between the second harmonic field and the polarization gating field associated in this setup, which is necessary for generating stable single isolated attosecond pulses.

Pulse duration measurements of grazing-incidence-pumped high repetition rate Ni-like Ag and Cd transient soft x-ray lasers.

We have measured the pulse duration of gain-saturated 13.9 nm Ni-like Ag and 13.2 nm Ni-like Cd transient collisional lasers excited by grazing-incidence-pumping for several pumping conditions. High-resolution streak-camera measurements yielded FWHM pulse durations close to 5 ps for both lasers under optimum pumping conditions. The very high brightness and short pulse duration of these new high repetition tabletop soft x-ray lasers make them an attractive source for dynamic applications.

An accumulative x-ray streak camera with 280-fs resolution

We demonstrated a significant improvement in the resolution of the x-ray streak camera by reducing the electron beam size in the deflection plates. This was accomplished by adding a slit in front of the focusing lens and the deflection plates. The temporal resolution reached 280 fs when the slit width was 5 mm. The camera was operated in an accumulative mode and tested by using a 25 fs laser with 2 kHz repetition rate and 1-2% RMS pulse energy stability. We conclude that deflection aberrations, which limit the resolution of the camera, can be appreciably reduced by eliminating the wide-angle electrons.

Carrier envelope phase effects on polarization gated attosecond spectra

Polarization gated high harmonic generation in argon gas was phase matched to produce a single or double pulses with 104 photons. It was accomplished by optimizing the argon gas pressure. The spectrum interference of the two pulses is affected by the carrier-envelope phase like in Youngs experiments. The XUV flux is sufficient for measuring the single shot XUV spectrum in the 33eV-55eV photon energy range. The spectral profile was a super-continuum for some shots and showed discrete high harmonics peaks for other shots. The carrier-envelope phase of pulses from grating-based chirped pulse amplification was also varied smoothly to cover a 2π range by controlling the grating separation. It is demonstrated that XUV spectra measures both the absolute value of the phase and the stability of the phase by measuring the phase with an f-to-2f setup and by the variation of XUV spectra from polarization gated high harmonics generation.

Generation of a 1 picosecond soft x-ray laser pulses from an injection-seeded plasma amplifier

Phase-coherent soft x-ray laser pulses of 1.13 ± 0.47 ps duration were generated by injection-seeding a solid-target Ne-like Ti plasma amplifier with high harmonic pulses. This is the shortest pulse duration reported to date from a table-top soft x-ray laser amplifier.

Picosecond Soft X-Ray Laser Pulses from an Injection-Seeded Plasma Amplifier

Phase-coherent soft x-ray laser pulses of 1.13 ± 0.47 ps duration were generated by injection-seeding a solid-target Ne-like Ti plasma amplifier with high harmonic pulses. This is the shortest pulse duration reported to date from a table-top soft x-ray laser amplifier.

Double optical gating of high harmonic generation

We propose a novel optical switch to control the high-order harmonic generation process so that single attosecond pulses can be generated with ~10 fs input pulses. The technique combines polarization gating and two-color gating.

Attosecond two-slit interference controlled by carrier-envelope phase

High harmonics generation was polarization gated with few-cycle laser pulses to produce two attosecond pulses with 104 XUV photons. The spectrum interference of the two pulses is affected by the carrier-envelope phase like in Young¿s experiments.

Effects of carrier envelope phase on single shot XUV supercontinuum measurements

Polarization gated high harmonic generation was phase matched to produce 104 XUV photons per shot. This allowed us to observe the dependence of the XUV supercontinuum on the carrier envelope phase of the laser pulses.