WO2009038608A2 - Temperature enhancement of x-ray radiation sources - Google Patents

Abstract

An apparatus and method for the temperature enhancement of an X-ray source to increase gain and efficiency is disclosed. The X-ray source has a target and produces therefrom an X-ray laser emission. The apparatus includes a nozzle configured to receive the target from an inlet end and to expel the target from an outlet end as atomic clusters, and a temperature controlled fluid input system. The temperature controlled fluid input system is provided for cooling the target and enhancing the collisional interactions in the target to increase the size and density of the atomic clusters formed from the target.

Description

TEMPERATURE ENHANCEMENT OF X-RAY RADIATION SOURCES

PRIORITY CLAIM

This application claims the benefit of U.S. Provisional Application Serial No. 60/936,882, filed June 22, 2007, under 35 U.S.C. § 119.

STATEMENT OF GOVERNMENT INTEREST This invention was made in part with government support under Grant

No. DAADl 0-0 l-C-0068 awarded by the Army Research Office via the Defense Advanced Research Projects Agency (DARPA). The government has certain rights in the invention.

TECHNICAL FIELD

The present invention relates to the field of X-ray energy sources and, in particular, to sources including Laser amplifiers that produce Xe(L) X-ray energy.

BACKGROUND ART

High energy X-ray sources, such as Laser amplifiers, have attracted interest in a number of economically significant fields. For example, the production of state of the art electronic devices can benefit from such sources. However, certain technical hurdles must be overcome to attain desired goals. High energy X-ray sources offer the promise of substantial improvement to photolithographic techniques used in the fabrication of silicon chips and other integrated circuits. With this process, light or other radiation from a specialized source is projected through a photomask of an electronic circuit. This produces an image of the circuit (or, more usually, a pattern of repeated copies of the image) on the semiconductor wafer. After exposure, the wafer is coated with a light-sensitive photoresist. Following development, unexposed areas of the photoresist layer are washed away, in preparation for an etching step that forms physical circuit details on the wafer surface. Usually, these steps are repeated numerous times to build up layers of circuit features in the semiconductor wafer. The challenge is to reduce the physical size of a circuit. As circuit details are made smaller, the wavelength of the light source must also be reduced accordingly. Advanced capability light sources currently operate in the deep ultraviolet (DUV) range, with wavelengths less than about 200 nanometers. Today, the quest is to develop commercially useful radiation sources that operate in the extreme ultraviolet (EUV) range with wavelengths as small as about 13.5 nanometers. Historically, this small nanometer wavelength portion of the electromagnetic spectrum has been characterized as soft X-rays. Previously, synchrotron sources have been used for research in this operating regime. However, these sources are very large and expensive. Smaller, more economical sources are needed to fuel continued economic growth. Moreover, it is desirable to increase x-ray amplifier emission of coherent X-ray sources. Additionally, a need exists for reliably producing amplification (i.e., gain) of X-ray sources in a controllable manner.

In the medical field, high resolution imaging is typically obtained using electron microscopy. However, resolution is limited and preparation of the objects being studied, usually tissue samples, is required. Accordingly, a need exists for a high resolution imaging source that reduces sample preparation time.

DISCLOSURE

The invention provides an apparatus and method for the temperature enhancement of an X-ray source to increase gain and efficiency of the radiation source, and to minimize the disadvantages associated with the prior art systems and provide advantages in construction, mode of operation and use. One embodiment of the X-ray source has a Xe target gas input and produces therefrom a Xe(L) X-ray laser emission. A system for providing the temperature improvement comprises a gas input system for enhancing the density and collisional interactions that enable the Xe clusters to be formed.

In one example, the gas input system comprises a temperature control system at the target gas input to control of the temperature of the region in which the Xe gas cluster medium is found and the amplification develops.

In another example, the gas input system comprises a temperature control system having a cooling stage at the amplifier gas input for cooling the Xe target gas.

In another embodiment, the invention provides a method for the temperature enhancement of an X-ray source to increase gain and efficiency. The X-ray source has a Xe target gas input and produces therefrom a Xe(L) X- ray laser emission. The method comprises controlling the temperature of the region in which the Xe gas cluster medium is found and the amplification develops. In one example, the step of controlling the temperature comprises cooling the gas input of the source.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: FIG. 1 is a schematic diagram of a signal representing saturated amplification detected from a plasma channel;

FIGS. 2(a)-2(d) are schematic diagrams of data showing temperature dependence of Xe(L) X-ray pulse intensity;

FIG. 3 is a schematic diagram showing temperature dependence of Xe(L) X-ray emission intensity;

FIG. 4(a) is a perspective view of an apparatus for enhancing an X-ray source to increase gain and efficiency according to principles of the invention;

FIG. 4(b) is an elevated side view of an apparatus for enhancing an X- ray source to increase gain and efficiency according to principles of the invention; and FIGS. 5a-5d are schematic diagrams illustrating improved operation of the X-ray amplifier of FIGs. 4(a) - 4(b).

BEST MODE FOR CARRYING OUT THE INVENTION Briefly, the invention includes an apparatus and method for generating ultrabright multikilovolt coherent X-ray radiation. Physical evidence is provided herein and includes the strong enhancement of selected spectral components of Xenon (i.e., Xe³⁵⁺ and Xe³⁷⁺) hollow atom transition arrays radiated axially from confined and enlarged plasma channels. Also provided are measurements of line narrowing that is spectrally correlated with the amplified transitions demonstrate amplification of multikilovolt X-rays for wavelengths between λ~ 2.7 IA and λ~ 2.93A.

The invention disclosed herein is, of course, susceptible of embodiment in many different forms. Shown in the drawings and described herein are preferred embodiments of the invention. It is understood, however, that the present disclosure is an exemplification of the principles of the invention and does not limit the invention to the illustrated embodiments.

For ease of description, energy producing equipment embodying the present invention is described herein in its usual assembled position as shown in the accompanying drawings, and terms such as upper, lower, horizontal, longitudinal, etc., may be used herein with reference to this usual position. However, the energy conversion equipment may be manufactured, transported, sold or used in orientations other than as described and shown herein.

The present invention provides an improved operation of X-ray radiation sources suitable, for example, in the semiconductor fabrication industry. Generation of ultrabright, multikilovolt coherent X-ray radiation resulting from amplification on hollow atom transition arrays is known and described in U.S. Patent Number 7,016,390, which is incorporated by reference herein. The present invention provides an improvement in the ability to produce and stably combine two new highly ordered forms of excited matter, hollow atoms and stable electronically hollow plasma channels. Hollow atoms refers to atoms (ions) that have an inverted electronic configuration and include one or more deeply bound inner-shell vacancies with the simultaneous retention of several electrons in relatively weakly bound outer orbitals. Such electronic states of the atoms facilitate prompt emission and amplification of X-rays. The capability of optical projection lithography, which has been used for high volume integrated circuit manufacture, is useful for patterning line widths as small as a fraction (e.g., ¹A) of a micron. However, based on current trends, the feature size of semiconductors decreases about 25 to 30 percent every other year, and therefore, new technologies will be required in the near future if circuit lines as small as 50 nanometers are to be realized. The present invention improves operation of X-ray sources that make practical lithography possible for mass semiconductor production.

By way of introduction, advanced energy sources, such as a Xe(L) X-ray laser radiation source operating at λ ~ 2.9 A have well documented [1-6] properties. This source is characterized by advanced coherent X-ray emissions made possible by the ability to controllably compress power to robust values that fall at or above the highest thermonuclear range (~10²⁰ W/cm³). In particular, such systems have been demonstrated to operate with saturated amplification in the multikilovolt (~ 4230-4570 eV) X-ray range on several Xe(L) transition arrays.

Referring now to FIG. 1, the schematic diagram shows the saturated amplification of such a system that has the specific ability to produce and controllably combine [7] two new highly ordered forms of excited matter, hollow atoms and stable electronically hollow plasma channels. Fig. 1 shows a signal obtained with laboratory scale apparatus that demonstrates saturated amplification on the Xe(L) hollow atom emission band from the Xe³⁵⁺ array (λ = 2.86 A) detected axially from a plasma channel of length ~2 mm with a focusing (~f/3) von Hamos spectrometer equipped with a mica crystal. The brightness of the source is estimated to be in the 10³¹-10³² γ-s^~l-mrrf²-mr^~2 (0.1% Bandwidth)^"1 range. For a gain exponent with the value g_o€ = 16, saturation is definitely reached [2]. The intensity represented by the ordinate incorporates proper account [1] of the response of the von Hamos spectrometer under conditions for which it records a spectrally sharp and spatially narrow X- ray beam with the simultaneous presence of a spectrally broad spontaneous emission spectrum that is radiated into 4π steradians. Temperature enhancement of Xe(L) X-ray production provides a number of benefits for practical radiation sources, such as X-ray amplifiers and the Xe(L) system referred to above. For example, although the characteristics of the Xe(L) system exhibit an exceptionally favorable power scaling [6], the findings described herein demonstrate that the emission, and consequently the amplification, can be sharply enhanced in a cost effective manner. This enhancement is provided by control of the temperature of the region in which the Xe gas cluster medium is found and the amplification develops.

The basic dynamic variables governing the compressible flow of a given material are the temperature (T/°C), preferably ranging between about 25°C and about -80°C, the pressure (P/bar), preferably ranging between about 1 and about 10 and the density

(p/cm^"3) preferably ranging between about 2.5xlθ¹⁹cm^"3 and about 2.5xl0²⁰cm^{' 3}. The temperature of the medium naturally influences both the density and the collisional processes. In the present case, the latter is very important, since it is the collisional interactions that enable the Xe clusters to be formed, which are the systems essential for amplification to be produced [I].

The data in FIGS. 2(a) - 2(d) illustrate the enhancement in both the strength of the X-ray emission and the length of the amplifying channel that occurs when the Xe nozzle temperature is reduced. FIGS. 2(a) - 2(d) show experimental data including (1) an enhanced signal strength and (2) the formation of longer amplifying channels, that result from cooling the Xe gas in the nozzle flow of the Xe(L) laser.

In FIG. 2(a), single pulse data are shown for a Xe plenum pressure of 1 15 psia at T = 297 K illustrating the Xe(L) spectrum and the associated channel image recorded by measuring the Xe(M) emission with a pinhole X- ray camera [I]. The incident energy of the 248 nm pulse was 410 mJ and the observed channel length was E ≡ 1.7 mm. In FIG. 2(b), data comparative to FIG. 2(a) are recorded with a Xe plenum pressure of 115 psia at a reduced temperature of T = 230 K. The incident 248 nm pulse was 400 mJ. A strongly enhanced spectrum and lengthened laser channel (C ≡ 2.25 mm) are evident. Moreover, in comparison with the spectrum shown in FIG. 2(a), the large enhancement of the signal in the λ ≡ 2.78-2.80 A region occurs, which corresponds to the spectral zone associated with (2s2p) double-vacancy states [3]. Also shown in FIGS. 2(c)-2(d) are laser propagations corresponding to FIGS. 2(a) and 2(b), respectively showing the increased channel length at the lower temperature of T=230K.

The net outcome concerning the intensity of emission is shown in the graph of FIG. 3. This graph demonstrates a dependence clearly favoring lower temperatures below room temperature of 297K. These temperatures can be easily, practically and controllably reached with the apparatus of FIGs. 4(a) - 4(b).

Referring now to FIGs. 4(a) - 4(b), a system, designated generally as 10, for enhancing an X-ray source to increase gain and efficiency by producing and stably combining hollow atoms and stable electronically hollow plasma channels is shown. The system 10 includes an apparatus 12 for forming densely packed Xe clusters that form a target (not shown). The apparatus 12 includes Xe input lines 14 that supply Xe gas to be formed into Xe clusters that are used as targets. The Xe clusters enable the creation of Xe hollow atom states. The Xe passes through the input lines 14 and into a cylindrically-shaped nozzle 16 having a nozzle aperture 18 at an outlet end 20. The Xe clusters are released from the nozzle aperture 18 as discrete units of media by solenoid actuators 22 located between the target gas input line 14 and nozzle 16. A control 24 operates the solenoid actuators 22, and is connected to the actuator via lead lines 26 (one connection is shown in FIG. 4(b) for simplicity). The solenoid actuators 22 can be pulsed to provide units of Xe gas to the nozzle 16. The control 24 operates (i.e., opens and closes) the solenoid actuators 22. The nozzle 16 is configured to receive the target from an inlet end 28 and expel the target as atomic clusters from the outlet end 20.

The Xe hollow atom states produce a characteristic Xe(L) spontaneous emission spectrum at λ=2.9A that arises from the excitation of densely packed Xe clusters with an intense pulse of 248nm X-ray laser radiation propagating in a self-trapped plasma channel. The channel is produced when the pondermotive potential pushes the free electrons out of the most intense part of the laser beam creating a positive index gradient at the beam center which augments the index gradient due to the relativistic mass increase of the electrons.

The X-ray laser delivers a light pulse, having an energy of about 400mj at a rate of 0.4Hz, and a temporal duration of about 230fs. The X-ray laser radiation is focused into the Xe clusters resulting in the release of X-ray and other electromagnetic radiation from the Xe clusters. Although the present embodiment uses Xe clusters, other materials can be used as a target such as Sulfur hexafluoride (SF₆), Tungsten hexafluoride (WF₆), and Uranium hexafluoride (UF₆). Generally, it is contemplated that other heavy elements/molecules having an atomic number Z greater than or equal to 50 can be used as targets. In the present embodiment the nozzle 16 is formed in a cylindrical shape, however it is envisioned that the nozzle can be formed in other geometrical shapes depending on the desired application. Additionally, it is desirable that the nozzle 16 is formed of a heat conducting material, for example a metal, to facilitate heat transfer as discussed below. The system 10 further includes an X-ray emission source, such as an X- ray laser amplifier or laser 30. In one embodiment, the laser produces a Xe(L) X-ray (λ ~ 2.9 A) laser emission when interacting with a Xe target. The laser 30 is provided in a generally horizontal direction as viewed in the drawing such that the laser directs a laser beam or beams (not shown) horizontally above the nozzle aperture 18. The nozzle aperture 18 is configured to release the Xe gas target as densely packed Xe clusters which the laser beams propagate there through. The nozzle aperture 18 is about 1.5 mm in width, although other widths are contemplated depending on the intended power output of the system 10. In the present embodiment, the Xe clusters are released from the nozzle aperture 18 in response to actuation of four solenoid actuators 22 that are located upstream of the nozzle packed Xe clusters and actuated in step with the laser beam from the laser 30. For example, the solenoid actuators 22 can operate to open and release densely packed Xe clusters prior to the laser 30 emitting a laser beam above the nozzle aperture 18. While four solenoid actuators are used with the present embodiment, it is contemplated that one or more solenoid actuators or other valve members can be used to provide the target to the nozzle 16.

The apparatus 12 a lso includes a temperature controlled fluid input system, designated generally as 32, which includes a coolant coil 34 having a coolant input 36 and a coolant output 38. The coolant input 36 connects to a source (not shown) which provides a coolant fluid to the temperature controlled fluid input system 32. In the present embodiment, a gas flows through the coolant coil 34 to cool the nozzle 16. The cooled nozzle 16 cools the target and enhances the collisional interactions in the target to increase the size and density of the atomic clusters formed in the nozzle. However, other fluids having different temperature characteristics may be either singly or in combination passed through the coolant coil to achieve specified temperatures in the range of 150K to less than 297K depending upon a particular application. As defined herein, a fluid can be either a liquid or gas.

A central section 40 of the coolant coil 34 encircles the nozzle 16 and is secured against the nozzle by clamp members 42. The clamp members 42 are each configured to receive a fastener 44 therethrough which secures each clamp member to the nozzle 16. The clamp members 42 can be formed with arcuate portions 46 that maintain the central section 40 of the coolant coil 34 in a fixed position such that the coolant coil remains in contact with the nozzle 16. The present embodiments has four clamp members 34 (two shown), however it is contemplated that more or less than four clamp members could be used to secure the coolant coil 34 to the nozzle 16. Moreover, it is also possible to provide grooves or other structure on the outer surface 48 of the nozzle 16 to keep the coolant coil 34 in close proximity to or in contact with the nozzle. It is also envisioned that the coolant coil 34 could be shaped to be in close proximity to or partially contacting the nozzle 16 depending on the selected material forming the coolant coil while still providing cooling to the nozzle.

In the present embodiment, the central section 40 is in direct contact with the nozzle 16 to facilitate heat transfer (i.e., cooling of the nozzle). Moreover, it is contemplated that the coolant coil 34 is formed of a material that facilitates transfer of heat from gases or fluids flowing through the coolant coil in the temperature range of 80K to less than 297K.

In the present embodiment, the coolant coil 34 encircles the nozzle 16 twice and has a nitrogen gas (N₂) flowing therethrough. However, other cooling gases/liquids may also be used to cool the nozzle and control the temperature of the nozzle in the range between 80K and less than 297K. Furthermore, although the coolant coil 34 is positioned to encircle the nozzle 16, other configurations are possible as long as cooling is provided between the nozzle and the coolant coil. Also, although the coolant coil 34 is positioned in the nozzle region, other embodiments can position the coolant coil upstream of the nozzle 16 as long as the temperature of the Xe cluster can be controlled. For example, it is envisioned that at least some enhancement of the gain and efficiency of an X-ray source would occur if the cooling coil is provided to a line (not shown) feeding Xe to the solenoid actuators 22.

An advantage of cooling the nozzle 16 in this manner is that the Xe clusters exiting the nozzle aperture 18 are more densely packed resulting in improved amplification of the laser beam (i.e., improved gain and efficiency). Moreover, since the cooling fluid which includes gases and/or liquids is confined within the coolant coil 34 it is possible to control the temperature of the nozzle more precisely than conventional systems which have no temperature control. The ability to easily and efficiently control the temperature allows for cooling of the nozzle 16 to prescribed temperatures. For example, the present temperature controlled fluid input system allows a nozzle temperature of 230K for Xe, which results in several advantageous effects. First, there is approximately a 2.5 fold enhancement of the Xe(L) hollow atom emission on the single-vacancy 3d— »2p charge state arrays. Second, amplifying self-trapped plasma channels with significantly enhanced lengths are produced. Third, a very sharply augmented emission on (2s2p) Xe(L) double-vacancy transitions in the λ~ 2.80A region occurs. Other materials can be similarly controlled at different temperatures that maximize the above effects for those materials. It is envisioned that a different number of turns and/or the diameter of the coolant coil 34 can be used to facilitate heat transfer between the coolant coil and the nozzle as is known to those skilled in the art of cooling. Moreover, although the coolant coil 34 is formed as a copper line, other metal lines or heat conducting materials may be used. The apparatus 12 has a solenoid actuated valve 50 positioned in the coolant coil 34 between the coolant input 36 and central section 40 for regulation of cooling gas/fluid flow through the coolant coil 34. The valve 50 is connected to the control 24 (connection not shown), and can be operated (i.e., opened and closed) by instructions from the control. In addition to the valve 50, the apparatus also has a thermocouple 52 connected to the nozzle 16 via a fastener 54. The thermocouple 52 is in contact with and configured to measure the temperature of the nozzle 16, and provides feedback via a pair of lead lines 56 (shown as one line) connected to the control 24 (connection not shown). The control 24 uses the feedback and generates instructions to the solenoid actuated valve 50 to control the temperature of the nozzle 16. In this manner, precise control of the temperature of the nozzle 16 can advantageously be achieved by use of the present apparatus 12.

Although the solenoid actuators 22, valve 50, and thermocouple 52 are connected to a single control 24, it is envisioned that multiple controls including a control for the laser 30 can be separately provided as stand alone controls or interconnected, depending on design choice. Moreover, although solenoid actuators and a solenoid actuated valve are used in the present embodiment, any type of valve capable of controlling gas/fluid flow through the nozzle 16 and coolant coil 34 are contemplated for use with the apparatus 12. The apparatus 12 of FIGs. 4(a)-4(b) produced the data shown in FIGs. 2(a) - 2(d) and FIG. 3. The apparatus 12 can be economically constructed and is simple to install and operate. It is also effective and scalable to larger sizes that would be appropriate for correspondingly increased X-ray powers.

Attention will now be directed to the ability of the present invention to provide enhanced production of Xe(L) (2s2p) double-vacancy states. The observation of enhanced production of Xe³⁷⁺(2s2p) double-vacancy states is a feature of an augmented power density [8]. In particular, the Xe³⁷⁺ double-hole states have exhibited strong amplification on 3d— »2p transitions in the λ = 2.78-2.81 A spectral region [3].

Turning now to FIGs. 5(a) - 5(d), the illustrated data show the prominence of double-vacancy (2s2p) excitations in the cooled spectra. FIG. 5(a) shows a single-pulse spectrum #32x04 exhibiting strong excitation of Xe³⁷⁺ (2 s2p) transition at λ = 2.80 A with the corresponding channel image visualized by a recording of the Xe(M) emission with an X-ray pinhole camera [I]. FIG. 5(b) shows a previously recorded (film #6) spectrum showing the amplification on the Xe³⁷⁺(2s2p) transition array [3]. FIG. 5(c) shows a spectral overlap of single-pulse spectrum #32x04 with that measured on film #6 from FIG. 5(b). FIG. 5(d) shows a corresponding laser propagation. Very good agreement is evident for the Xe³⁷⁺ (2 s2p) feature at λ s 2.80 A. Other significant corresponding spectral features are also visible, for example, the strong lines at λ ~ 2.6 A.

As can be seen, FIGS. 5(a) - 5(d) provide a comparison of a single-pulse spectrum recorded at a temperature of T = 230 K with a previously recorded [3] spectrum illustrating amplification on the Xe³⁷⁺(2s2p) transition at λ ≡ 2.804 A. The precise overlap of the amplified feature shown on film #6 with the strong narrow signal on the single-pulse spectrum #32x04 confirms the presence of strong double-vacancy excitation in the cooled spectrum. Furthermore, with reference to FIG. 2, we observe, in the comparison of panels (a) and (b), that the strength of the double-vacancy 3d→2p transitions prominent in the cooled spectrum shown in panel (b) taken at T = 230 K is greater than the peak intensity seen in panel (a) for the corresponding single-vacancy lines. Accordingly, the enhancement in the double-vacancy features is highly sensitive to the temperature and exhibits an increase that is considerably greater than that shown by the single-vacancy transitions in the λ = 2.85 A region. Although further studies are certainly required, with reference to the concept of a critical cluster size developed in earlier work [9], we believe that the larger average cluster size expected at the reduced temperature is the basis of this observation.

In conjunction with the above-described apparatus, it can be appreciated that a method for generating laser radiation having increased efficiency and gain in the X-ray region of the electromagnetic spectrum can be done using the system shown in FIGs. 4(a)-4(b), and includes the following steps: generating a target in a first region; transferring the target to a second region; controlling a temperature of the second region such that the temperature of the second region is less than the first region; transferring the target to a third region; generating laser radiation of a selected intensity and size; and directing the laser radiation into the target in the third region whereby the target comprises atomic clusters having an increased average cluster size and density.

The method can be implemented such that the temperature of the second region is in a range of 150K to less than 297K. Additionally, the atomic clusters can be selected from the group consisting of Xe, SF₆, UF₆, and WF₆ and other heavy elements/molecules having an atomic number Z greater than or equal to 50. The laser radiation can also be an X-ray laser radiation.

The method can also optionally include a step of measuring the temperature in the second region. A step of adjusting the temperature in the second region based on the measured temperature in the second region may also be included. The foregoing description and the accompanying drawings are illustrative of the present invention. Still other variations and arrangements of parts are possible without departing from the spirit and scope of this invention. Artisans will recognize broader aspects and additional features and variations of the invention from the description of the preferred embodiment above. Example claims are presented to illustrate the scope of the example embodiment.

PUBLICATIONS

1. "Ultrabright Multikilovolt Coherent Tunable X-ray Source at λ ~ 2.71-2.93 A," Alex B. Borisov, Xiangyang Song, Fabrizio Frigeni, Yevgeniya Koshman, Yang Dai, Keith Boyer, and Charles K. Rhodes, J. Phys. B36, 3433 (2003).

2. "Saturated Multikilovolt X-ray Amplification with Xe Clusters: Single- Pulse Observation of Xe(L) Spectral Hole Burning," Alex B. Borisov, Jack Davis, Xiangyang Song, Yevgeniya Koshman, Yang Dai, Keith Boyer, and Charles K. Rhodes, J. Phys. B36, L285 (2003). 3. "Amplification at λ ~ 2.8 A on Xe(L) (2s2p) Double- Vacancy States

Produced by 248 run Excitation of Xe Clusters ^n Plasma Channels," Alex B. Borisov, Xiangyang Song, Ping Zhang, Arati Dasgupta, Jack Davis, Paul C. Kepple, Yang Dai, Keith Boyer, and Charles K. Rhodes, J. Phys. B38, 3935 (2005). 4. "Explosive Supersaturated Amplification on 3d->2p Xe(L) Hollow

Atom Transitions at λ ~ 2.7-2.9 A," Keith Boyer, Alex Borisov, Xiangyang Song, Ping Zhang, John C. McCorkindale, Shahab Khan, Yang Dai, Paul C. Kepple, Jack Davis, and Charles K. Rhodes, J. Phys. B38, 3055 (2005). 5. "Single-Pulse Characteristics of the Xe(L) Amplifier on the Xe³⁵⁺ (3d→

2p) Transition Array at λ ≡ 2.86 A," Alex B. Borisov, Xiangyang Song, Ping Zhang, John C. McCorkindale, Shahab F. Khan, Richard DeJonghe, Sankar Poopalasingham, Ji Zhao, Keith Boyer, and Charles K. Rhodes, J. Phys. B39, L313 (2006). 6. "Double Optimization of Xe(L) Amplifier Power Scaling at λ ~ 2.9A,"

Alex B. Borisov, Xiangyang Song, Ping Zhang, John C. McCorkindale,

Shahab F. Khan, Richard DeJonghe, Sankar Poopalasingham, Ji Zhao,

Yang Dai, and Charles K. Rhodes, J. Phys. B40, Fl 31(2007).

7. "Ultrahigh Power Compression for X-ray Amplification: Multiphoton Cluster Excitation Combined with Non-Linear Channelled Propagation," A. B. Borisov, A. McPherson, B. D. Thompson, K. Boyer, and C. K. Rhodes, J. Phys, B28, 2143 (1995).

8. "Intensity Dependence of the Multiphoton-Induced Xe(L) Spectrum Produced by Subpicosecond 248 nm Excitation of Xe Clusters," A. B. Borisov, A. McPherson, K. Boyer, and C. K. Rhodes, J. Phys. B29, L43

(1996).

9. "Multiphoton Induced X-ray Emission and Amplification from Clusters," A. McPherson, T. S. Luk, B. D. Thompson, K. Boyer, and C. K. Rhodes, Appl. Phys. B57, 337 (1993).

Claims

1. An apparatus for enhancing an X-ray source to increase gain and efficiency, the X-ray source having a target and producing therefrom an X-ray laser emission, comprising: a nozzle configured to receive the target from an inlet end and to expel the target from an outlet end as atomic clusters; and a temperature controlled fluid input system for cooling the target and enhancing the collisional interactions in the target to increase the size and density of the atomic clusters.

2. The apparatus of claim 1 , wherein the temperature controlled fluid input system comprises: a coolant coil configured to receive a cooling fluid therethrough; and wherein said coolant coil has a portion thereof in contact with said nozzle to cool said nozzle.

3. The apparatus of claim 2, wherein said cooling fluid is N₂.

4. The apparatus of claim 2, wherein said temperature controlled fluid input system further comprises: a control configured to regulate a flow of the cooling fluid through said cooling line; and a solenoid actuated valve located upstream of said portion of said coolant coil and connected to said control, wherein said solenoid actuated valve operates between open and closed positions in response to instructions from said control.

5. The apparatus of claim 4, further comprising a thermocouple in contact with said nozzle and configured to measure a temperature of said nozzle and provide feedback to said control, wherein the control receives said feedback and generates instructions to said solenoid actuated valve based on said feedback to control a temperature of said nozzle.

6. The apparatus of claim 5, further comprising one or more clamp members for fastening said portion of said coolant coil in direct contact with said nozzle.

7. The apparatus of claim 6, wherein said coolant coil is cylindrical and each of the clamp members has at least one arcuate portion configured to receive said coolant coil.

8. The apparatus of claim 1, wherein the target is selected from the group consisting of Xe, SF₆, UF₆, WF₆, an element having an atomic number Z > 50, and a molecule having an atomic number Z > 50.

9. The apparatus of claim 1, wherein said apparatus further comprises: one or more solenoid actuators connected to said inlet end of said nozzle and receiving the target from an input line, said solenoid actuators configured to release a discrete unit of the target into said nozzle; and a nozzle aperture located at said outlet end for condensing the atomic clusters.

10. The apparatus of claim 1, wherein said nozzle has a temperature in a range of 8OK to less than 297K.

11. A method for generating laser radiation having increased efficiency and gain in the x-ray region of the electromagnetic spectrum, comprising the steps of: generating a target in a first region; transferring said target to a second region; controlling a temperature of said second region such that said temperature of said second region is less than said first region; transferring said target to a third region; generating laser radiation of a selected intensity and size; and directing the laser radiation into said target in said third region, wherein said target comprises atomic clusters having an increased average cluster size and density.

12. The method of claim 1 1, wherein said temperature of said second region is in a range of 8OK to less than 297K.

13. The method of claim 1 1 , wherein said atomic clusters are selected from the group consisting of Xe, SF₆, UF₆, WF₆, an element having an atomic number Z > 50, and a molecule having an atomic number Z > 50.

14. The method of claim 11, wherein said laser radiation is an X-ray laser radiation.

15. The method of claim 1 1, further comprising a step of measuring the temperature in said second region.

16. The method of claim 15, further comprising a step of adjusting the temperature in said second region based on said measured temperature in said second region.

17. An apparatus for the temperature enhancement of an X-ray source to increase gain and efficiency, the X-ray source having a Xe gas target and producing therefrom a Xe(L) X-ray (λ ~ 2.9 A) laser emission, comprising a cooling gas input system for enhancing collisional interactions that enable Xe clusters to be formed from said Xe gas target.

18. The apparatus of claim 17, wherein said cooling gas input system comprises a temperature control system to control the temperature of a nozzle that the Xe clusters form in prior to amplification of the laser emission.

19. The apparatus of claim 18, wherein the temperature of said nozzle is in a range of 80K to less than 297K.

20. The apparatus of claim 18, wherein said temperature control system includes a thermocouple configured to measure a temperature of said nozzle and a control connected to said thermocouple such that temperature feedback from said thermocouple causes said control to adjust the temperature of said nozzle.