Capillary Discharge Soft X-ray Laser Research Articles

Impact of pre-pulse current and delay time on 46.9 nm laser with larger inner diameter alumina capillary

In this Letter, we firstly, to the best of our knowledge, demonstrated the influence of pre-pulse current and delay time on the intensity of a discharge pumped Ne-like Ar soft X-ray laser operating at 46.9 nm by employing an alumina capillary having an inner diameter of 4.8 mm. Specifically, the delay time was changed from 8 to 520 μs in small intervals. The pre-discharge current was increased from 25 A to 250 A through small steps, while keeping the main discharge current constant. Usually, a small pre-discharge current is applied to an Ar-filled capillary to attain a plasma column having sufficient pre-ionization before the injection of the main current. The pre-discharge current of 140 A was declared the best current to obtain lasing with a 4.8 mm diameter capillary. The laser spots were captured at best time delays for the pre-discharge currents of 25, 45, 80, 140, and 250 A, which support the experimental results. We observed that by applying the pre-discharge current of 140 A, the laser spot exhibits small divergence, higher symmetry, and uniformity, which is clear evidence of strong amplification. The laser spot obtained at 140 A is cylindrically symmetric and has a better structure than those reported by all other groups in the literature. Hence, the laser spot indicates that the laser beam is highly focusable and beneficial for the applications of the 46.9 nm laser. Results of this Letter might open a new way to enhance applications of a 46.9 nm capillary discharge soft X-ray laser.

Impact of discharge currents on the intensity of 46.9 nm capillary discharge soft X-ray laser.

In this article, capillary discharge Ne-like argon 46.9nm soft X-ray laser has been firstly manifested with 4.8mm inner diameter alumina capillary for higher discharge currents. We have designed and installed capillary discharge setup for 4.8mm inner diameter alumina capillary to achieve intense 46.9nm laser. One dimensional Langragian Magneto-hydrodynamics (MHD) code was used to simulate the plasma conditions at the lasing time. The MHD code was used to perform the parametric studies of Z-pinch argon plasma, such as electron temperature, electron density and Ne-like argon ion density. The intensities of capillary discharge 46.9nm laser emitted from 4.8mm inner diameter alumina capillary were measured at 30, 36 and 40kA main discharge currents. According to the results, when the main current amplitude was increased from 30kA to 36kA and 40kA, the intensity of laser produced at optimum pressure increased up to 1.5 and 2 times, respectively. Moreover, we also studied the influence of predischarge current by increasing the predischarge current from 25 to 250A and investigated 140A as the best predischarge current for lasing. Hence, increasing the amplitude of main current using a comparatively larger inner diameter capillary is an effective way to improve intensity of capillary discharge 46.9nm soft X-ray laser. The maximum energy of 46.9nm laser was observed approximately 1.5mJ under best discharge conditions. The discussion has been made on the enhancement of 46.9nm laser intensity for higher main discharge currents and best predischarge current with experimental and simulated results. This is the first observation of 46.9nm laser with 4.8mm inner diameter alumina capillary.

Impact of discharge current profile on the lasing efficiency of 46.9 nm capillary discharge soft x-ray laser

The very important role played by the discharge current profile on the lasing efficiency of 46.9 nm capillary discharge soft x-ray laser has been experimentally established. The discharge current profile was varied either by making the current faster and keeping its peak value fixed or by increasing its peak value and keeping the duration fixed. When the dI/dt value was increased from 7.5 × 1011 to 9.2 × 1011 A s−1 by making the current faster, the soft x-ray laser efficiency was found to be enhanced significantly. This was reflected by a substantial increase (~48%) in the gain-coefficient of the x-ray laser from 0.69 cm−1 to 1.02 cm−1 respectively. The effect of current amplitude on the gain-coefficient was also studied by measuring the gain-coefficient for different current amplitudes while keeping the duration fixed. It was found that there exists an optimum value of discharge current amplitude at which the gain-coefficient becomes maximum. Using such optimization, the gain-coefficient could be further enhanced to 1.33 cm−1 which is ~93% higher than the earlier value of 0.69 cm−1.

Formation of nanostructures induced by capillary-discharge soft X-ray laser on BaF2 surfaces

BaF2 was ablated by a capillary-discharge pumped soft X-ray laser at 46.9nm focused by a toroidal mirror at a grazing incidence of 83°. The damaged area, induced by both single and multiple laser pulses, was determined to be covered with fringe-like nanostructures with spacings of approximately 400nm and mastoid nanostructures with diameters of approximately 600nm. In this study, we analyze the morphology of the detected damage patterns and discuss the damage mechanism. Results indicate that the depth of the nanostructures varies with different pulse numbers and laser power densities.

Influence of the gain-length product on the pulse duration of highly saturated capillary discharge soft X-ray laser

In this paper, the variation of the pulse duration was investigated for the highly saturated capillary discharge Ne-like Ar 46.9 nm soft X-ray laser. The evolutions of the pulse duration along the axis of capillary were measured for the 3.2- and 4.0-mm-inner-diameter alumina capillaries. Then, the simulations for the evolution of pulse duration were conducted with consideration of the saturation effect of laser amplification, showing good consistency with the experimental results. The analysis was performed on the variation of pulse duration over plasma length, indicating that the variation of the gain-length product caused the evolution of the pulse duration. Meanwhile, the evolutions of pulse durations were measured for different initial Ar pressures for both capillaries, showing the pulse durations were wider near the optimum pressure. Based on the simulations and the experimental results, it is concluded that the variations of the pulse duration of the soft X-ray laser were mainly due to the effect of gain-length product.

毛细管放电氩等离子体的电离价研究

毛细管放电软X射线激光或极紫外光刻光源研究中等离子体的电离价是一个重要的参量，它决定光源的波长。依据毛细管放电的特点以及参考文献中提供的数据推导出毛细管放电氩等离子体电离价的经验公式。利用国内首台毛细管放电极紫外光刻光源演示装置研究了氩等离子体的光谱，实验表明峰值~28 kA的脉冲电流对30 Pa氩气放电或峰值~34 kA的脉冲电流对40 Pa氩气放电都产生了Ar7+。而公式计算出30 Pa和40 Pa时分别需要24.4~39 kA和32.7~52.3 kA的峰值电流。这说明经验公式具有一定的实用意义。 Ionized degree of Ar plasma in capillary discharge soft X-ray laser or Extreme Ultraviolet Lithographic (EUVL) source research was an important parameter which determined the wavelength of the plasma source. According to the characteristics of capillary discharge and the data from literature, we deduced an experiential expression of ion-ized degree of Ar plasma in capillary discharge by analogy method. With the first set of capillary discharge EUVL source demonstrative device in China, the spectra of Ar plasma was studied. It was found from experiment that either 30 Pa Ar gas discharged by peak pulse current of -28 kA or 40 Pa Ar gas discharged by peak pulse current of -34 kA could produce Ar7+ ion. While the simulating results showed that it was necessary for the 30 Pa and 40 Pa Ar gas to be ionized to Ar7+ ion by peak pulse current of 24.4 - 39 kA and 32.7 - 52.3 kA respectively. These results proved that the experien- tial expression had some definite practical significance.

Ar气气压对毛细管放电软X光激光输出的影响

Ar气气压是毛细管放电软X光激光研究中的关键参量，其对激光的产生机理和输出等发挥重要的作用。本文通过系统地研究Ar气气压对激光输出的影响，发现当Ar气气压从38 Pa升高到65 Pa时，激光信号的最大输出值确实从~17 V提高到~18.4 V。但前提条件是适当地增大预脉冲电流，并适当地延长预–主脉冲延时，使主脉冲电流能够更充分地利用良好的预电离等离子体状态，获得增益系数较大的激光介质。这些研究工作对进一步优化放电参量，提高激光的输出功率等具有重要的意义。 Ar pressure was such a key parameter in capillary discharge soft X-ray laser research that it played important role in generating mechanism and output and so on of laser. Through systemic investigation of the impact of Ar pressure on laser output in this article, it was found that the maximum output of laser signal had really been increased from ~17 V to ~18.4 V when Ar pressure went up from 38 Pa to 65 Pa. But the prerequisite was to increase the pre-current pulse and to prolong the delay time between pre- and main-current pulse properly which could make the main-current pulse utilize the better state of pre-ionized plasma adequately and obtain the laser medium with larger gain coefficient. These research works had important significance in optimizing the discharge parameter further and improving the output power of laser and so on.

The Spectrum of Ne-Like Ar and the 4d-4p Transition of Kr7+ at 45 nm in Capillary Discharge Experiment

ABSTRACT Capillary discharge soft X-ray laser, which is always called “table-top soft X-ray laser,” is one of the effective methods for miniaturization. The method is deemed to have experimental facility with practicable value. With capillary discharge mechanism, Ne-like Ar at 46.9 nm soft X-ray laser has been obtained, and the experimental results and the analyses are reported in this paper. Experimentally, a current pulse with the amplitude of 20 kA was used to excite three different gases: Ar, Kr, and N2. The signals were detected by an X-ray diode (XRD), and the emission spectra were monitored with a Rowland spectrograph. The J = 0–1 line and one 3d-3p transition of Ne-like Ar were detected, with wavelengths of 46.9 nm and 48.5 nm, respectively. Adjusting the pure Ar to the appropriate pressure, the authors found that the J = 0–1 line gains amplification, while 3d-3p does not. When the Ar pressure was 26 Pa, the J = 0–1 line completely dominated the spectrum. N2 and Kr were used as the materials of capillary discharge respectively. The spike signal was obtained by XRD, then the spectrum was detected by Rowland spectrograph, and the spectrum of Kr7+ was found.

Highly efficient pulsed power supply system with a two-stage LC generator and a step-up transformer for fast capillary discharge soft x-ray laser at shorter wavelength

Highly efficient and compact pulsed power supply system for a capillary discharge soft x-ray laser (SXRL) has been developed. The system consists of a 2.2 microF two-stage LC inversion generator, a 2:54 step-up transformer, a 3 nF water capacitor, and a discharge section with a few tens of centimeter length capillary. Adoption of the pulsed transformer in combination with the LC inversion generator enables us to use only one gap switch in the circuit for charging the water capacitor up to about 0.5 MV. Furthermore, step-up ratio of a water capacitor voltage to a LC inversion generator initial charging voltage is about 40 with energy transfer efficiency of about 50%. It also leads to good reproducibility of a capillary discharge which is necessary for lasing a SXRL stably. For the study of the possibility of lasing a SXRL at shorter wavelength in a small laboratory scale, high-density and high-temperature plasma column suitable for the laser can be generated relatively easily with this system.

Method to eliminate the damage aroused by intrinsic prepulse of Blumlein transmission line in capillary discharge soft X-ray laser system

To raise the utilization ratio of the energy power, and meanwhile, guarantee the waveform of the main discharge current to obtain X-ray laser, our capillary discharged Ne-like Ar soft X-ray laser system adopts Blumleim transmission line (BTL) and a 300 kV-Marx generator; and by using our self-developed intrinsic-prepulse elimination device and extrinsic-prepulse generator, we successfully removed the intrinsic prepulse of BTL, and thus eliminated its deteriorative effect towards Z-pinch plasma. By this means, we obtained stable X-ray laser output; and the voltage transmission rate of our system nearly reaches 122%, which provides a guarantee for the miniaturization of the power source and the whole system.

Capillary discharge soft X-ray lasing in Ne-like Ar pumped by low main current pulses

Under the condition of the low main current pulse, the capillary discharge soft X-ray laser is obtained. The laser energy of the same discharge current amplitude at different Ar pressures and of different current amplitudes at the same Ar pressure are compared, respectively. At different Ar pressures, the amplitude of the main current pulse evidently impacts the soft X ray, especially at a pressure higher than 30 Pa. In order to obtain the laser output at a high Ar pressure, the amplitude should be increased. However, at the same Ar pressure, it might have an optimum current, in which case the laser spike is the highest and the most stationary. The laser achieving time at different amplitudes is also discussed. As far as we know, this is the first time the influence of the amplitude of the main current pulse has been analyzed.

Soft X-Ray Laser Interferometry of Colliding Laser-Created Plasmas in Semicylindrical Cavities

A tabletop capillary discharge soft X-ray laser was used to acquire high-contrast interferograms that map the evolution of dense aluminum plasmas created by the laser irradiation of a 500-mum-diameter semicylindrical cavity with 120-ps optical laser pulses of ~1.1 times 1012 - W ldr cm-2 peak intensity. The measured electron density maps, which were compared with simulations, show that the plasma converges on axis where it collides to form a localized region with density exceeding 1 times 1020 cm-3.

Dynamics of converging laser-created plasmas in semicylindrical cavities studied using soft x-ray laser interferometry

The evolution of dense aluminum and carbon plasmas produced by laser irradiation of 500-microm -diam semicylindrical targets was studied using soft x-ray laser interferometry. Plasmas created heating the cavity walls with 120-ps -duration optical laser pulses of approximately 1x10;{12}Wcm;{-2} peak intensity were observed to expand and converge on axis to form a localized high-density plasma region. Electron density maps were measured using a 46.9-nm -wavelength tabletop capillary discharge soft x-ray laser probe in combination with an amplitude division interferometer based on diffraction gratings. The measurements show that the plasma density on axis exceeds 1x10;{20}cm;{-3} . The electron density profiles are compared with simulations conducted using the hydrodynamic code HYDRA, which show that the abrupt density increase near the axis is dominantly caused by the convergence of plasma generated at the bottom of the groove during laser irradiation.

Prediction and observation of tin and silver plasmas with index of refraction greater than one in the soft x-ray range

We present the calculated prediction and the experimental confirmation that doubly ionized Ag and Sn plasmas can have an index of refraction greater than one for soft x-ray wavelengths. Interferometry experiments conducted using a capillary discharge soft x-ray laser operating at a wavelength of confirm that in few times ionized laser-created plasmas of these elements the anomalous dispersion from bound electrons can dominate the free electron contribution, making the index of refraction greater than one. The results confirm that bound electrons can strongly influence the index of refraction of numerous plasmas over a broad range of soft x-ray wavelengths confirming recent observations. The understanding of index of refraction at short wavelengths will become even more essential during the next decade as x-ray free electron lasers will become available to probe a wider variety of plasmas at higher densities and shorter wavelengths.

Effect of pre-pulses on capillary discharge soft x-ray laser

On a capillary discharge setup lasing in Ne-like Ar at 46.9nm, the ablation of c apillary wall was investigated for polythene and alumina material at both of inh erent 2—5kA-pre-pulse of setup and separate pre-pulse of 20A by measuring soft x ray emission from the capillary discharged. For inherent pre-pulse and polythe ne capillary, the ablation is too large to create uniform plasma columns and it is impossible to obtain lasing. In the case of 20A-pre-pulse and alumina capilla ry, the ablation decreased remarkably and the laser spike pulse was distinguishe d on an x-ray diode because the uniform Z-Pinch plasma column had formed.

Role of the wall ablation in the operation of a 46.9 nmAr capillary discharge soft x‐ray laser

AbstractA capillary discharge pumped soft x‐ray laser operating at 46.9 nm on the 3p–3s transition of the Ne‐like Ar has been realized by pumping the active medium with a relatively slow current pulse (dI/dt ≈ 6 · 1011 A/s). In order to study the role of the ablation in the production of the laser effect, the intensity of the amplified 46.9 nm line has been investigated using the same pumping current pulses in the plastic (polyacetal) and ceramic (Al2O3). We showed that the ablation of the capillary walls is unfavorable both for the compression and stability of the plasma and consequently for the soft x‐ray laser production. The amplification and lasing effects are observed only in the ceramic channel. The measurements of the line intensity at 46.9 nm showed the lasing with a gain‐length product of ≈ 9, a laser pulse energy of ≈ 5 μJ, a pulse duration of 1.3 ns and a beam divergence of ≈ 3.5 mrad. In addition, effect of the scaling of the time of lasing with the initial plasma diameter was demonstrated experimentally and compared with a one‐dimensional MHD model.

Extremely compact soft X-ray lasers based on capillary discharges

Extremely compact high repetition rate soft X-ray lasers based on capillary discharge excitation have demonstrated average powers of a few milliWatt at 46.9nm, milli-Joule-level pulse energy, peak spectral brightness several orders of magnitude larger than third-generation synchrotron beam lines, and excellent spatial coherence. Examples of the use of a capillary discharge soft X-ray laser in dense plasma diagnostics and laser ablation of materials are summarized.

Wavefront measurements in the soft X-ray range

In this article we report a new wavefront sensor, developed at the Laboratoire de Spectroscopie Atomique et Ionique, for a full characterization of soft X-ray beams. The Shack-Hartmann sensor has a theoretical accuracy in the order of at a wavelength around 13 nm. A cartography of the wave-vectors pointing of laser-pumped soft X-ray laser has been achieved. It has shown the presence of many ripples probably coming from plasma instabilities. Capillary discharge soft X-ray laser has been also investigated. For all the pumping configurations, the wavefront is spherical, divergent with a radius of about 6.5 m at 2.5 m from the plasma end. The best wavefront exhibits an error to a perfect wave of 3λ rms. Assuming to focus the beam with a f = 50 mm diffraction-limited mirror, a theoretical focal spot size of 0.5 μ m in diameter have been estimated containing 70% of the incident energy. In that case an intensity of 4 × 10 13 W cm −2 should be achieved.

Capillary discharge soft X-ray laslng in Ne-like Ar pumped by long current pulses

A capillary discharge soft X-ray laser operating at 46.9 rim on the transition 3p–3s (J=0−1) of the Ne-like Ar has been realized by exciting the active medium with a long half-cycle duration current pulse of 140 ns. The current is produced by discharging a 10 nF water dielectric capacitor, initially charged to voltages lower than 200 kV by a six stage Marx generator, through a 15-cm long capillary channels. The laser amplification has been obtained by properly adjusting all the other experimental parameters. Utilizing a 3-mm in diameter AI2O3 capillary channel initially filled with 0.3 torr of Ar pressure, a laser beam, which has a 4-mrad divergence and a time duration of 1.3 ns, is characterized by a gain of 0.6 ± 0.1 cm−1. The stability of the plasma compression followed by the laser emission is verified.

Probing of the active layers in a capillary discharge soft X-ray laser at 18.22 nm

Lasing on the Balmer- α line of C VI at 18.22 nm has been established earlier by inducing an MHD instability in an ablative capillary made of polyacetal. Employing a multilayer mirror the beam from one end is now reflected back into the plasma column and used to probe the active medium. Amplification is confirmed but depends on the time the beam re-enters the plasma, allowing thus to infer a lifetime of the active layers of about 400 ps. From the laser pulse with the mirror positioned 3 cm from the end of the plasma column a gain length product of GL=4.3 is derived.