Imaging Michelson interferometer for a low-density gas jet characterization

Abstract

A new optical probing method with increased interferometric sensitivity for a low-density gas jet characterization is presented. The proposed technique employs a Michelson interferometer with a self-imaging object arm, which enables the relay imaging of the object on itself, and in this way, the phase sensitivity of the device is increased by a double propagation of the object laser beam through the gas jet. The wavelength of 405 nm was chosen to further increase the sensitivity by increasing the probe wavenumber. A low-density argon gas jet with various backing pressures was characterized by our method and by a commonly used Mach-Zehnder interferometer setup showing the expected twofold increase in the signal to noise ratio in the double pass configuration.

Multi-pass probing for high-sensitivity tomographic interferometry

“…We can define the sensitivity of the given setup in terms of variation of the area density as per 16 , where is the uncertainty of the gas number density, L is the length of the gas medium, and N denotes the number of passes. In the case of Ar, we obtain sensitivities of , , and for a single-pass, two-pass, and four-pass setup, respectively, and in the case of He we get, , , and for a single-pass, two-pass, and four-pass setups, respectively.…”

“…Note that instead of the shearing Wollaston interferometer a different method to assess the phase distortion of the beam can be used for the presented multi-pass probing setup, e.g. the high-resolution wave-front sensor based on multi-beam lateral shearing interferometry 16 , 26 or a shearing interferometer with an air wedge 27 . One can also employ one of the digital holography methods 28 to reconstruct the field of the probe in the object plane, in particular its phase, without imaging the object on the camera.…”

“…A Michelson interferometer with up to 8-passes 15 shows an increase in phase sensitivity, but limits its applicability to axially symmetric objects with small refractivity and low requirements on spatial resolution. Relay imaging in the object arm of a double-pass Michelson interferometer introduced in 16 allowed increase of sensitivity without affecting the high spatial resolution of the method. Another trend is the use of tomography for three-dimensional reconstruction of tailored gas density distributions 17 – 20 .…”

Tomographic characterization of gas jets for laser-plasma acceleration with increased sensitivity

“…The optical source, a 405 nm monomode fiber laser, collimated by a singlet lens to a 20 mm laser beam diameter, enters the interferometer setup from the left. Due to the shorter wavelength of the laser compared to the conventionally used He-Ne laser (632.8 nm), a higher phase sensitivity is obtained due to larger wavenumber and higher refractive index of the Ar gas [19]. The collimated laser beam is partially transmitted through a 50/50 beamsplitter and travels to the weakly refracting gas jet, placed in a vacuum chamber.…”

Update on laser-driven X-ray sources at ELI Beamlines

“…The typical gases for the LPA target are pure He, He with the admixture of Nitrogen, gas clusters, or dry air [20], and the plasma density for the acceleration will be in the order of 10 18-19 cm -3 . The gas jets are characterized using a high resolution, high -sensitivity interferometer [21]- [22] before being placed into the experimental chamber. The ultrashort pulses (~fs) of Gammatron sources and their efficient synchronization with another femtosecond laser pulse offer a versatile tool in studying various time-resolved experiments in ultrafast science.…”