In this study, we examine the quality of microscale ghost images as a function of the measured histographic signal distribution of the speckle fields from a nonuniform pseudothermal light source. This research shows that the distribution of the detected signal level on each pixel of the camera plays a significant role in improving the contrast-to-noise ratio (CNR) of pseudothermal ghost imaging. To our knowledge, the scaling of CNR with different pixel intensity distributions of the speckle fields is observed for the first time in the field of pseudothermal microscale ghost imaging. The experimental observations are in very good agreement with numerical analysis. Based on these findings, we can predict the settings for light sources that will maximize the CNR of microscale ghost images.
Summary form only given. Light beams carrying an isolated point singularity with a screw-type phase distribution are called an optical vortex (OV) (Fig 1). The fact that in free space the Poynting vector of the beam gives the momentum flow leads to an orbital angular momentum (OAM) of the photons in such a singular beam, independent on the spin angular momentum [1]. There are many applications of optical OAM shown in literature that would benefit from the availability of optical vortex beams in all spectral regions. For example it was shown that transitions forbidden by selection rules in dipole approximation appear allowed when using photons with the additional degree of freedom of optical OAM [2]. However, the common techniques of producing new light frequencies by nonlinear optical processes seem problematic in conserving the optical vortex when the nonlinearity becomes large.We show that with the extremely nonlinear process of High Harmonic Generation (HHG) it is possible to transfer OVs from the near-infrared to the extreme ultraviolet (XUV) [3] at wavelengths down to ~30 nm.We use a conventional HHG setup, where Harmonics down to the 27th are produced in Argon gas by exposing it to ultrashort 30 fs laser pulses at 800 nm wavelength. In order to impose a helical phase front onto these driving pulses, we used a spatial light modulator (Fig 2). The observed light of several plateau harmonics was examined spatially and spectrally, while also two different tools to investigate the phase structure were employed. The spatial profile showed the expected singular behaviour, a dark region in the centre, although two separate "lobes" of intensity were observed. A phase feature that showed a shift of on opposing sides of the beam profile was found with a wavefront splitting technique. A screw-like phase evolution around the profile was also verified by employing a Hartmann type measurement.The generated spectrum revealed that in all Harmonic orders an OV was present. The profile however looked the same in all orders, indicating identical topological charge, which runs counterintuitive to the assumption that the phase of is multiplied by the order of the nonlinearity.
Broadband supercontinuum generation mediated by non-adiabatic mode dispersion profiles resulting in new type of soliton dynamics in dispersion-designed antiresonant hollow-core fibers is reported. A new concept of soliton explosion is demonstrated in experiment and simulation.
We evaluated the capabilities of an intense ultrafast high-harmonic seeded soft X-ray laser at 32.8 nm wavelength regarding single-shot lensless imaging and ptychography. Additionally the wave front at the exit of the laser plasma amplifier is monitored in amplitude and phase using high resolution ptychography and backpropagation techniques.Characterizing the laser plasma amplifier performance depending on the arrival time of the seed pulse with respect to pump pulses provides insight into the light plasma interaction in the soft X-ray range.
Ultrafast coherent phonon dynamics in ZnO is studied via high-order harmonic generation by intense mid-IR laser pulses. We show, the phonon dynamic is very different after excitation in the tunnel and multiphoton regime.
In this study, the influence of speckle size on contrast-to-noise ratio (CNR) and resolution is examined based on the object dimensions in the macroscopic and microscopic regimes. This research shows that for microscopic samples the conventional scaling laws are no longer effective and the CNR does not counter-propagate in the same manner as the resolution. To our knowledge, a deviation in CNR scaling on speckle size is observed for the first time in the field of microscopic ghost imaging. This result was verified using two different sample shapes. In addition, numerical analysis revealed that the noise of the photodiode is a limiting factor for the CNR. Based on these findings, the conditions for identifying the parameter set that maximizes the CNR and provides high resolution images was defined, which achieving high-quality microscopic ghost images.
