D. Phalippou

Applications of wavefront division interferometers in soft x rays

The development of soft x‐ray interferometry demands high quality optical elements and high brightness sources. However, the balance between these two requirements depends on the exact nature of the interferometer setups. Generally speaking, amplitude division interferometers require beam splitters, the optical quality of which remain a big technological issue. On the contrary, the high brightness sources needed by wavefront division interferometers are readily available, and will progress in the near future. Examples of such interferometers are given for various applications in development or in project.

Interferograms obtained with a X-ray laser by means of a wavefront division interferometer

Abstract A wavefront division interferometer has been used for the first time with a soft X-ray laser (λ = 21.2 nm). The experiment aims to demonstrate X-ray laser interferometry in this configuration and to investigate the phase shifting measurement accuracy as well. The X-ray laser is generated in a neon-like zinc plasma in which it makes two passes thanks to a multilayer mirror half-cavity. The X-ray pulse duration is ≈50 ps. The beam has a very high brightness (≈4 × 10 15 W cm −2 sr −1 in 0.01% bandwidth) which allows us to place the interferometer far from the source (2.8 m) and thus to benefit by a large transverse coherence width. The interferometer consists of a Fresnel bi-mirror which adds coherently one part of the X-ray laser beam section to the other one. Single laser-shot interferograms of a reflecting sample provided with a λ 2 dephasing step (51.7 nm height) have then been successfully recorded. The phase shifting accuracy resulting from the smallest observable fringe change is about λ 20 .

Demonstration of phase contrast in scanning transmission X-ray microscopy: Comparison of images obtained at NSLS X1-A with numerical simulations

Unlike transmission X-ray microscopy, scanning transmission X-ray microscopy (STXM), till now, does not allow phase contrast. Several method have been suggested but no proof of practical feasibility has been yet given. Here we analyze the methods based on the detection of the small beam deflection induced by the object phase gradient, by a segmented detector. It is shown that structuring the zone plate illumination potentially improves the detection. A diffractive beam profiler has been constructed to condition the beam of the NSLS X1A STXM. Recent images are shown, which, compared to numerical simulations, indicate the presence of phase contrast.

Internal frequency conversion extreme ultraviolet interferometer using mutual coherence properties of two high-order-harmonic sources

We report on an innovative two-dimensional imaging extreme ultraviolet (XUV) interferometer operating at 32 nm based on the mutual coherence of two laser high order harmonics (HOH) sources, separately generated in gas. We give the first evidence that the two mutually coherent HOH sources can be produced in two independent spatially separated gas jets, allowing for probing centimeter-sized objects. A magnification factor of 10 leads to a micron resolution associated with a subpicosecond temporal resolution. Single shot interferograms with a fringe visibility better than 30% are routinely produced. As a test of the XUV interferometer, we measure a maximum electronic density of 3x10(20) cm(-3) 1.1 ns after the creation of a plasma on aluminum target.

A High Precision Scanning Control System For A VUV Fourier Transform Spectrometer

A VUV Fourier transform spectrometer based on a wavefront division interferometer has been built. Our ultimate goal is to provide a high resolution absorption spectrometer in the 140 – 40 nm range using the new third generation French synchrotron source Soleil as the background continuum. Here, we present the design and latest performance of the instrument scanning control system. It is based on multiple reflections of a monomode, frequency‐stabilized HeNe laser between two plane mirrors allowing the required sensitivity on the displacement of the interferometer mobile arm. The experimental results on the sampling precision show an rms error below 5 nm for a travel length of 7.5 mm.

A FOURIER TRANSFORM SPECTROMETER WITHOUT BEAM SPLITTER FOR THE VUV–EUV RANGE

We describe a Fourier transform spectrometer designed to operate down to 60 nm on a synchrotron beam line. As far as we know, there is no such instrument available in the EUV (λ < 140 nm) partly because manufacturing accurate beam splitters remains the major difficulty at these wavelengths. We use a wave front division interferometer instead of an amplitude division one to overcome this difficulty. The interferometer is based on a modified Fresnel bimirror configuration, which is controlled by an original optical system. This system keeps the mirror tilt error to a negligible value during mirror translation, and provides a sensitive interferometric measurement of the mirror translation. The sampling interval is 29 nm (path difference), allowing one to record large band spectra down to λ = 58 nm with spectral resolution δσ = 0.33 cm-1 for 512 K samples (one-sided interferograms). We measured the apparatus function by recording an interferogram from a He–Ne stabilized laser. By studying the white noise in the corresponding spectrum, we found that the sampling error in the interferogram was about 0.4 nm rms, which produces a near-perfect apparatus function. Finally, we recorded the visible/near UV spectrum of an arc mercury lamp for illustration.

Usefulness of X-ray lasers for science and technology

Recent realization of saturated X-ray lasers (XRLs) has considerably extended the range of optical properties of soft X-ray sources toward high brightness and large coherence length. Consequently, new results may be expected from studies previously experienced with traditional sources such as synchrotron radiation. On the other hand, XRLs open new fields of research owing to their high brightness. In this paper, we present some of the first experiments utilizing XRL sources.

Development and applications of X‐ray lasers at LSAI/LIXAM

We present an overview of our research activity achieved since the last X‐ray laser Conference in Saint‐Malo. Our research program involves the development of laser‐pumped collisional X‐ray lasers under different regimes of irradiation, and the use of these sources for applications. The work presented involves a number of French and international collaborations and was carried out at different pump laser facilities: LULI (Ecole Polytechnique), LOA (ESNTA) in France; Rutherford Laboratory in U.K; PALS in Czech Republic.

Multi‐millijoule, highly coherent X‐ray laser at 21 nm as a routine tool for applications

A recently developed double‐pass, deeply saturated Ne‐like Zn X‐ray laser at 21.2 nm, is presented. The system consists of a 3‐cm long plasma and a half cavity constituted by a flat multilayer mirror located at 8.5 mm. The pump sequence includes a weak prepulse and a main heating pulse, delivering ∼500 J of net energy at 1.315 μm, in pulses with a length of ∼450 ps. A novel prepulse illumination geometry is employed, in which the prepulse beam generates a wide preplasma buffer into which subsequently a much more tightly focused main beam is coupled. The emitted X‐ray beam is narrowly collimated and possesses a remarkably high spatial quality. In the half‐cavity regime, the system provides an output energy of about 4 mJ, corresponding to peak power of 40 MW. A fully routine operation of the half‐cavity has been achieved, making it possible to perform, without any realignment or manual intervention, about 100 shots with one multilayer mirror.

Near-field imaging of Ni-like silver transient collisional x-ray laser

We review our recent progress in the development of transient x-ray lasers and of their application to plasma diagnostic. The first observation of C-ray laser emission at the new PHELIX-GSI facility is reported. This TCE X-ray laser will be a promising tool for heavy-ion spectroscopy. We then present the main results obtained at the LULU-CPA facility with a compact high-resolution X-UV imaging device. This device was used to investigate the spatial source structure of the Ni-like silver transient X-ray laser under different pumping conditions. The key-role of the width of the background laser pulse on the shape of the emitting aperture is demonstrated. Finally the imaging device was used as an interference microscope for interferometry probing of a laser-produced plasma. We describe this experiment performed at APRC-JAERI.