Propagation of ultrashort laser fields with spatiotemporal couplings using Gabor's Gaussian complex decomposition.

In ultra-intense chirped pulse amplification laser systems, pulses of ultrashort duration and high energy are generated using large spectral bandwidths and large beam diameters. Hence, the spatiotemporal couplings of the laser field can become significant and affect the field structure. The propagation of such pulses is simulated in this work using a code developed in-house, based on Gabor's decomposition of the initial complex field into Fourier transform limited Gaussian pulse beam terms. Subsequently, the analysis of the temporal, spatial, and angular chirp, as well as pulse front tilt couplings for a super-Gaussian beam of 25 fs duration allows quantification of their signatures in the near field and focus.

Free space variable optical attenuator using frustrated total internal reflection with 70 dB dynamic range.

With the advance of high power laser systems, there is an increasing need to dim the corresponding light field power over larger dynamic ranges. The usual means to control the attenuation of directed light use optical filters or coatings with tailored reflectance and transmittance properties. They do not provide the variability that is often required in experiments. A system is reported here that demonstrated continuous variation of the transmittance over 70 dB, using frustrated total internal reflection.

Non-collinear spectral coherent combination of ultrashort laser pulses.

Non-collinear spectral coherent combining (NCSCC) of ultrashort pulses is analyzed. 2D modeling of the electromagnetic field is performed in case of NCSCC using two or three pulses with different wavelengths. In the case of two pulses, a potentially unwanted spatio-temporal structure of the field appears, corresponding to spatial and temporal modulation of the pulse. By using NCSCC of three 62 fs long pulses with different spectral composition, such spatial-temporal coupling is eliminated and the combined pulse duration in the focal region drops to less than half. The method is scalable to a large number of ultrashort pulses.

One long and two short pumping pulses control for plasma x-ray amplifier optimization.

Development of efficient soft x-ray laser plasma amplifiers adapted to seeded operation, requires a better control over amplifier transverse spatial extent, brilliance control and gain lifetime. Here it is shown that pumping the plasma amplifier with one long and two short pump pulses (1L2S) provides advantages in terms of control for the specified parameters in the case of Ni-like Ag x-ray laser. Also, significant tunability of the gain lifetime in the 1L2S pumping scheme for Ne-like Ti x-ray laser is observed. Direct harmonics seeding and chirped harmonics seeding amplification approaches may benefit from the control of the gain lifetime, in terms of better use of the pump energy and as a way to reduce the amplified spontaneous emission in x-ray lasers.

Phase measurement in long chirped pulses with spectral phase jumps.

Characterization of the chirp in stretched laser pulses is performed with a novel, simple method, based on the use of a plasma mirror switch coupled with a spectrometer. For a 36nm full width half maximum bandwidth and 360ps chirped laser pulse, the spectral phase of the pulse was measured in few hundred of points. Besides the chirp measurement, the approach allows the detection of jumps in the optical path, hence spectral phase jumps corresponding to less than 3ps.

Q-switched laser-assisted grazing incidence pumping (QAGRIP) for efficient soft x-ray laser generation.

We have investigated a new scheme for laser plasma transient collisional soft x-ray lasers based on the use of an additional laser to produce the preplasma. Soft x-ray emission measurements made for different solid targets are presented and discussed. A significant enhancement of the SXRL emission as compared to double-pulse single-beam grazing incidence (DGRIP) using the same pump laser is reported for 13.9- and 32.6-nm SXRL wavelengths.

Thin film beam splitter multiple short pulse generation for enhanced Ni-like Ag x-ray laser emission.

An alternative, novel multiple pulse generation scheme was implemented directly after the optical compressor output of an x-ray pump laser. The new method uses a polarization sensitive thin film beam splitter and a half-wavelength wave plate for tuning the energy ratio in the multiple short pulses. Based on this method, an extensive study was made of the running parameters for a grazing incidence pumped silver x-ray laser (XRL) pumped with a long pulse of 145 mJ in 6 ns at 532 nm and up to 1.45 J in few picoseconds at 810 nm. Fivefold enhancement in the emission of the silver XRL was demonstrated using the new pump method.

Pump energy reduction for a high gain Ag X-ray laser using one long and two short pump pulses.

A pump scheme with one long and two short pump pulses is proposed, in a grazing incidence pumping x-ray laser (XRL) configuration. A 360 ps long pulse, prepares a plasma in a low charge state. Then, an initial short pulse ionizes the plasma to an optimal charge state, while the second short pulse induces strong collisional excitation in the gain region. With only 200 mJ of pump energy on target, a compact Ag XRL at 13.9 nm with a gain coefficient of 55 cm(-1) was achieved.

Optimal main pulse angle for different preplasma conditions in transient collisionally pumped x-ray lasers.

The effects of the incidence angle of the main pump (MP) pulse in non-normal pumping geometry and the influence of the MP duration are investigated experimentally and theoretically for a transient collisionally pumped (TCE) x-ray laser in Ni-like Zr at 45 degrees and 72 degrees incidence angle on the target. The way they transfer to the x-ray laser output depends on the preplasma conditions, most notably on the average ionization distribution at the arrival of the MP. Moreover, contrary to previous grazing incidence pumping results, it is found that the shortest attainable MP maximizes the output. Modeling of the experimental results is performed with EHYBRID code. The results are important for scaling high repetition-rate non-normal incidence pumped lasers to sub- 10nm wavelengths.