二加二維激光加工機(jī)機(jī)械及控制系統(tǒng)設(shè)計,二加二維激光加工機(jī)機(jī)械及控制系統(tǒng)設(shè)計,二維,激光,加工,機(jī)械,控制系統(tǒng),設(shè)計 DOI: 10.1007/s00340-004-1529-z Appl. Phys.B (2004) Lasers and Optics Applied Physics B f.yan 1 j.zhang 1,a117 x.lu 1 j.y.zhong 1,2 Similarity of plasma conditions of some Ne-like X-ray lasers and their partner Ni-like X-ray lasers 1 Laboratory of Optical Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080, P.R. China 2 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, P.R. China Received: 31 October 2003/Revised version: 29 March 2004 Published online: 20 May 2004 Springer-Verlag 2004 ABSTRACT Plasma conditions for the Ni-like Ag, Cd, In, Sn, Sb X-ray lasers and the Ne-like Fe, Co, Ni, Cu, Zn X-ray lasers are studied, using a one-dimensional hydrodynamic code. The results suggest that the main hydrodynamic characteristics and plasma conditions of these Ni-like X-raylasers and their corres- ponding partner Ne-like X-ray lasers are similar. This similarity enables us to predict the performance of some Ni-like X-ray lasers using rather simple simulations of their partner Ne-like X-ray lasers. PACS 52.25.Jm; 52.50.Jm; 42.55.Vc; 82.20.Wt 1 Introduction Since the first demonstration of the amplification of X-ray lasers in a laboratory using the collisional excitation scheme 1, tremendous progress has been made in the devel- opment of X-ray lasers using the prepulse technique 26. The saturated output of X-ray lasers has been demonstrated atwavelengthslessthan 10nm7,8.Ultra-shortpulsepump- ing has significantly enhanced the efficiency to drive X-ray lasers 912. Due to high quantum efficiency, Ni-like X-ray lasers, in principle, have a more favorable scaling of laser wavelength withdriveenergythanNe-likeX-raylasers13.However,the population kinetics of Ni-like ions in general is much more sensitivetoplasmaconditionsthanthatofNe-likeions.More- over, it is more difficult to calculate atomic data of Ni-like ions because of the complicated level structure. By compari- son, some codes has been developed to successfully simulate Ne-likeX-raylasers,forexample,LASNEX14,JB-1915, Med10316. Inthis paper bycomparing the hydrodynamic characteris- tics of plasma conditions for X-ray laser Ni-like and Ne-like plasma conditions, we find a similarity of plasma conditions between some Ni-like X-ray lasers and their partner Ne-like X-ray lasers. Based on this similarity we can predict the per- formance of some Ni-like X-ray lasers using rather simple hydrodynamicandatomicsimulationsoftheirpartnerNe-like X-raylasers. a117 Fax: +86-10/82649356, E-mail: 2 Simulation of plasma conditions of the Ne-like Fe and Ni-like Ag X-ray lasers Simulations are carried out in this paper using the code MED103, which is a one-dimensional Lagrangian hy- drodynamic code. The validity of the code in the description of laser-plasma interaction has been demonstrated by many experiments and simulations 17,18. In the simulations we use Gaussian pulses at 1.053m and 100-m-thick slab tar- gets. The drive pulse duration is set at 2nsand the peak irra- diance is optimized to produce optimum plasma condition. In our previous work 19, we optimized the preplasma conditions forthe Ne-like Fe (25.5nm, 3p 3s, J = 0 1) X-ray laser. An optimized plasma condition was achieved with a large Ne-like ion abundance and a high gain of the X-ray laser. The same drive condition is used in this paper to calculate the plasma condition of the Ni-like Ag X-ray laser. Figure 1 gives the contours of ion abundance vs space and FIGURE 1 Contours of ion abundance vs space and time for Ni-like Ag (a) and Ne-like Fe ions (b). The color in the figure from lightness to dark stands for an ion abundance over 10%, 50%, 70%, respectively. The time of the peak irradiance is at 3000 ps and the target surface is at 100m Applied Physics B Lasers and Optics FIGURE 2 Contours of ion abundance vs space and time for the Co-like Ag ions (a) and the F-like Fe ions (b). The color from the light to the dark stands for the ion abundance over 1 %, 5%, 10% (a) and 1 %, 3 %, 5%, r es pectively FIGURE 3 Contours of ion population density vs space and time for the Ni- like Ag and the Ne-like Fe X-ray lasers. The color from lightness to dark represents the ion population density over 110 17 cm 3 ,110 18 cm 3 , 110 19 cm 3 , respectively time for Ni-like Ag (a) and Ne-like Fe (b) ions, respectively. The target surface is located at 100m and the drive pulse reaches its peak at 3000ps in Fig. 1. Both the Ne-like Fe and the Ni-like Ag X-ray lasers can reach high ion abundance (70%) under the same drive conditions. Their distribution contours in space and time are similar, although for the Ne- FIGURE 4 Contours of electron temperature for the Ni-like Ag and Ne-like Fe X-ray lasers vs. space and time like Fe case, the area for high ion abundance is lager and appears earlier in time. The next higher ionization stage of the Co-like ions and F-like ions are also calculated under the same drive condition. As shown in Fig. 2, the ion abundance of the Co-like Ag ions reaches 10% while the F-like Fe ions only reaches 5%. In order to avoid over-ionization, we carry out another calculation at reduced drive irradiance. When the maximum ion abundance of the Co-like Ag ions equals that of the F-like Fe (5%) ions, the Ni-like Ag ion abundance is toolowtoachieveanoptimum plasmaconditionforhighgain operation. This implies that it is necessary to tolerate some- what over-ionization for an optimum operation of the Ni-like Ag X-ray laser. Figure 3 gives the contours of ion population density vs. space and time for the Ni-like Ag and the Ne-like Fe ions. These two contours in space and time are similar. TheiondensityoftheNi-like Agions at110 19 cm 3 region has less space/time extent than that of the Ne-like Fe ions, due to the larger Co-like Ag ion population than the F-like Fe ion population. Figure 4 shows the contours of the electron temperature (T e ) for the Ne-like Fe and the Ni-like Ag X-ray lasersvsspaceandtime.Asimilarityalsoexistsindistribution shape though the electron temperature for the Ni-like Ag case is lower than that for the Ne-like Fe X-raylaser. 3 Simulation of Ne-like Fe and Ni-like Ag X-ray laser We have analyzed the plasma conditions for the Ne-like Fe and Ni-like Ag X-ray lasers. Next we calculate the localgainfortheNe-likeFeandNi-likeAgX-raylasersbased on the results obtained inthe above section. In our previous work 19, we optimized the preplasma conditions for the Ne-like Fe X-ray laser (25.5nm, 3p 3s, J = 0 1).Under anoptimum preplasma condition gen- erated by laser beam focused at 610 11 W/cm 2 in 2ns YAN et al. Similarity of plasma conditions of some Ne-like X-ray lasers and their partner Ni-like X-ray lasers FIGURE 5 Contours of local gain for the Ni-like Ag X-ray laser vs. space and time pulses, a main pulse with 1ps duration and 110 15 W/cm 2 peak irradiance was followed. When the de- lay time between the two pulses is zero, a gain with a value higher than 150cm 1 was generated. In this paper, we investigate the Ni-like Ag X-ray laser at 13.9nm(4d 4p, J = 0 1) using the MED103 code coupled with an atomic data package. We treat the plasma conditions of Ne-like Ag ions obtained in above section as preplasmaconditions.Thepeakirradianceandthedurationof the main pulse and the delay time between the prepulse and the main pulse are optimized to generate high gain. We find that high gain can be generated using a 1psmain drive pulse at 110 15 W/cm 2 peak irradiance when the delay time be- tween the prepulse and main pulse is 1.0ns. Figure 5 gives contours of local gain vs space and time for the Ni-like Ag X-ray laser. The main drive pulse reaches its peak at 4000ps. The color from the light to the dark represents gain over 50, 100,150 cm 1 , respectively. From the result we can conclude that high gain operation can occur under the plasma condi- tions obtained in the above section, the same as those for the Ne-like Fe X-ray laser. The conclusion also further verifies thatthere is asimilarity ofplasma conditions between the Ne- like Fe and the Ni-like Ag X-raylasers. 4 Simulation of other partners of Ne-like and Ni-like X-ray lasers Similarly, we simulate the preplasma conditions fortheNe-likeCo,Ni,Cu,ZnX-raylasers.Thelaserpulsedu- ration is fixed at 2nsand the peak irradiance is optimized in ordertogenerateoptimum conditions forhighgainoperation. Theoptimized intensities are shownin Table 1. The plasma conditions under the corresponding drive irradiance for the above elements have high Ne-like ion abundance (70%)andlowF-like ion abundance. Comparing with the plasma conditions for the Ne-like Fe X-ray laser, we conclude that high gain operation can occur under these Elements Fe Co Ni Cu Zn Drive irradiance 0.6 0.8 1.2 1.7 2.1 (10 12 W/cm 2 ) TABLE 1 The optimized irradiance for some Ne-like X-ray lasers plasma conditions. Using the drive intensities in Table 1, plasma conditions for their partner Ni-like X-ray lasers are simulated. By analyzing ion abundance electron temperature and ion population density, our simulations show that the plasma conditions for the Ni-like Cd, In, Sn, Sb X-ray lasers under the corresponding drive intensities (0.8,1.2,1.7,2.1, (10 12 W/cm 2 ) are also suitable to produc high gain. We compare the Sn plasma condition and Cu plasma condi- tion obtained under the same drive condition (2ns and 1.710 12 W/cm 2 ). Figure 6 gives the distribution of ion abundance vs. space-time for the Ni-like Sn ions and the Ne-like Cu ions. Similar to the distribution for the Ne-like Fe ions and the Ni-like Ag ions, the Ne-like (Ni-like) ion abundance reaches 70% population. Figure 7 shows the dis- tribution of ion abundance vs space and time for the Co-like Sn ions and F-like Cu ions. The ion abundance of the Co- like Sn ions is larger than that of the F-like Cu ions. This shows the overionization is easier to happen for the Ni-like X-raylasers.Figure8showsthedistributionofionpopulation density vs space and time for the Ni-like Sn and the Ne-like Cu X-ray lasers. The two ion population distribution region in space/time are similar, especially in the density region of about 110 18 cm 3 . Figure 9 describes the distribution of electron temperature vs. spaceand time for theNi-like Sn and Ne-like Cu X-ray lasers. Although with a lower temperature and a narrower region in space and time for the Ni-like Sn X-ray laser, the T e distribution is similar to that of the Ne-like Cu X-ray laser. Comparison of the plasma conditions of these Ne-like X-ray lasers with their partner Ni-like X-ray lasers show that there is a similarity of plasma conditions between some Ne- like X-ray lasers and their partner Ni-like X-ray lasers. The FIGURE 6 Contours of ion abundance vs space-time for the Ni-like Sn (a) and the Ne-like Cu (b). The color in the figure from lightness to dark represents the ion abundance over 10%, 50%, 70% Applied Physics B Lasers and Optics FIGURE 7 Contours of ion abundance vs space-time for the Co-like Sn (a) andF-likeCuX-raylaser(b). The color from the light to the dark represents the ion abundance over 10%, 15%, 20% (a) and 1%, 5%, 10% FIGURE 8 Contours of ion population density vs space and time for the Ni- like Sn and the Ne-like Cu X-ray lasers. The color from the light to the dark represents the ion population density over 110 17 cm 3 ,110 18 cm 3 , 110 19 cm 3 , respectively similarity also applies to plasma conditions of Ne-like Co X-ray laser and Ni-like Cd plasma conditions, etc. as shown in Fig. 10. The arrows represent the similarity relation be- tween these Ne-like X-ray lasers and their partner Ni-like X-ray lasers. The degree of similarity is generally weakened from the left to the right. The main reason is that the Ni-like FIGURE 9 Contours of electron temperature for the Ni-like Sn and the Ne- like Cu X-ray lasers vs space and time. The color from the light to the dark stands for the electron temperature over 100 eV, 200 eV, 250 eV FIGURE 10 Similarity between Ni-like plasma and Ne-like plasma. The thinner lines stands for weakened similarity ions are much easier to be over-ionized to the next ionization stage than the Ne-like ions with the increase of atom num- ber. Although the degree of similarity is weakened generally with the increase of atom number, this still reflects a part- nership between some Ne-like plasma conditions and their partner Ni-like plasma conditions under certain drive condi- tions. Because of the lower value and narrower region of ion abundance, population density and electron temperature for the Ni-like case, we can predict that the Ni-like X-ray lasers generally have lower gain and smaller high gain region than the Ne-like X-raylasers under the samedrive conditions. 5 Comparision of the electron configuration of some Ne-like ions and their partner Ni-like ions Ne-like ions have ten bound electrons, which con- figureagroundstatewith1s 2 2s 2 2p 6 closedshells.Population ofthe3plevelsisprovidedthroughcollisionalexcitationfrom the ground state, cascading from higher-n states, and a com- bination ofthree-bodyradiativeanddielectron recombination YAN et al. Similarity of plasma conditions of some Ne-like X-ray lasers and their partner Ni-like X-ray lasers Fe Fe 15+ : 489.3Fe 14+ : 457 Ag Ag 18+ : 499 Ag 17+ : 469 Co Co 16+ : 546.8Co 15+ : 512 Cd Cd 19+ : 544 Cd 18+ : 513 Ni Ni 17+ : 607.2Ni 16+ : 571 In In 20+ : 592 In 19+ : 559 Cu Cu 18+ : 671 Cu 17+ : 633 Sn Sn 21+ : 641 Sn 20+ : 607 Zn Zn 19+ : 737 Zn 18+ : 689 Sb Sb 22+ : 691 Sb 21+ : 657 TABLE 2 Ionization energy for some ions (eV) from the F-like ions. Electrons in the n = 3 shell will usu- ally rapidly decay back to the ground state by fast 3s 2por 3d 2p dipole transitions. The 3p electrons are radiatively metastable to the ground state. Inversion is hence created on various 3p 3s transitions in the Ne-like ions. Similar to Ne-like X-ray ions, Ni-like ions also have a closed outer shell. In Ni-like X-ray lasers, the upper laser level 3d 9 4d 1 S 0 is populated through the monopole colli- sional excitation from the ground state 3d 10 1 S 0 , the strong lasing lines are dominated by the 3d 9 4d 1 S 0 3d 9 4d 1 P 1 and 3d 9 4d 1 S 0 3d 9 4d 3 D 1 transitions. The energy level interval between4dand4plevelsfortheNi-likeionsislargerthanthat between 3pand 3s levels for the Ne-like ions whilethe bound energyofthegroundstateforNi-likeandNe-likeionsis simi- lar. This leads to higher quantum efficiency for Ni-like X-ray lasers than Ne-like X-raylasers. To further understand this similarity, we also compare the ionization energy for these Ne-like ions with their partner Ni- like ions used in the above sections. The ionization energy in Table 2 is calculated by Cowan and MCDF atomic-physics packages. The ionization energies for Fe 15+ ions and Ag 18+ ions are 489.26eV and 499eV, respectively. And the ioniza- tion energy of Fe 14+ ions is close to that of Ag 17+ ions. So we conclude that the pumping condition for Ne-like and Ni- like X-ray laser is similar. According to the values in Table 2, there is a similar correspondence between the Ne-like X-ray laser ions and Ni-like ions, in which the ionization energy for Ne-like Fe, Co, Ni ions are more similar to that of Ag, Cd, In ions than the paris of Ne-like Cu, Zn and that of Ni-like Sn, Sb ions. Therefore the conclusion drawn from the compari- son of the ionization energy supports the conclusion from the hydrodynamicsimulation. 6Conclusion WehavesimulatedtheplasmaconditionsoftheNi- likeAg,Cd,In,Sn,SbX-raylasersandtheNe-likeFe,Co,Ni, Cu,ZnX-raylasers.Bycomparingthehydrodynamiccharac- teristicsofionabundance,ionpopulationdensityandelectron temperature for the Ni-like Ag, Sn and the Ne-like Fe, Cu X-raylasersindetail, oursimulationsshowthatthereisasim- ilarity of plasma conditions between some Ne-like and their partner Ni-like X-ray lasers. 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