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Design and experimental validation of a compact collimated Knudsen source

Steinar H. W. Wouters, G. ten Haaf, Peter H. A. Mutsaers, Edgar J. D. Vredenbregt

Published Nov 24, 2015• 0 citations
OpenAlex

Abstract

In this paper we discuss the design and performance of a collimated Knudsen source which has the benefit of a simple design over recirculating sources. Measurements of the flux, transverse velocity distribution and brightness at different temperatures were conducted to evaluate the performance. The scaling of the flux and brightness with the source temperature follow the theoretical predictions. The transverse velocity distribution in the transparent operation regime also agrees with the simulated data. The source was found able to produce a flux of $10^{14}$ s$^{-1}$ at a temperature of 433 K. Furthermore the transverse reduced brightness of an ion beam with equal properties as the atomic beam reads $1.7 \times 10^2$ A/(m${}^2$ sr eV) which is sufficient for our goal: the creation of an ultra-cold ion beam by ionization of a laser-cooled and compressed atomic rubidium beam.

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Design and experimental validation of a compact collimated Knudsen source

Steinar H. W. Wouters, G. ten Haaf, Peter H. A. Mutsaers +1 more

In this paper we discuss the design and performance of a collimated Knudsen source which has the benefit of a simple design over recirculating sources. Measurements of the flux, transverse velocity distribution and brightness at different temperatures were conducted to evaluate the performance. The scaling of the flux and brightness with the source temperature follow the theoretical predictions. The transverse velocity distribution in the transparent operation regime also agrees with the simulated data. The source was found able to produce a flux of $10^{14}$ s$^{-1}$ at a temperature of 433 K. Furthermore the transverse reduced brightness of an ion beam with equal properties as the atomic beam reads $1.7 \times 10^2$ A/(m${}^2$ sr eV) which is sufficient for our goal: the creation of an ultra-cold ion beam by ionization of a laser-cooled and compressed atomic rubidium beam.

arXiv:1511.07790•Nov 24, 2015•0 citations

Design and experimental validation of a compact collimated Knudsen source

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In this paper, the design and performance of a collimated Knudsen source, which has the benefit of a simple design over recirculating sources, is discussed. Measurements of the flux, transverse velocity distribution, and brightness of the resulting rubidium beam at different source temperatures were conducted to evaluate the performance. The scaling of the flux and brightness with the source temperature follows the theoretical predictions. The transverse velocity distribution in the transparent operation regime also agrees with the simulated data. The source was tested up to a temperature of 433 K and was able to produce a flux in excess of 10(13) s(-1).

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In the ultracold FIB project a high brightness ion beam is developed for usage in a focused ion beam (FIB) source. This Focused Ion Beam can be used in applications where milling, imaging and deposition at the nanoscale needs to be done with increasing demands on control and resolution. The generation of the ion beam done in three stage principle. The first stage is the generation of the atomic beam and this is the subject of this work. The following stages first transversely cool and compress the atomic beam by using laser cooling techniques and then ionize and accelerate the atoms to form the ion beam. The generation of the atomic beam is done using a Knudsen cell; an effusive oven containing a vapor of rubidium atoms. The pressure difference between the vapor pressure in the oven and the vacuum outside the oven generates a flow of atoms from the oven to the vacuum. Only atoms that have a low transverse velocity can be captured by the laser cooling stage and will attribute to the ion beam. Therefore it is important to minimize the divergence in the beam and to this extent a collimating tube is used to connect the effusive oven to the vacuum system. The collimating tube minimizes beam divergence and compared to other collimating mechanisms it reduces the amount of rubidium loss, therefore greatly increasing the lifetime of the system.In order to measure the transverse velocity distribution, the transverse beam profile and the total flux, Laser-Induced Fluorescence measurements have been performed. These measurements show that the source generates an atomic beam with a particle flux ranging from 107 s-1 at a source temperature of 60 ºC to 1010 s-1 at a source temperature of 160 ºC. The flux is lower than predicted by theory and the transverse velocity distribution is broader than predicted by theory. However, the particle flux is stable within 1% and the installation of an active temperature controller promises to improve this stability even further. In the ultracold FIB project a high brightness ion beam is developed for usage in a focused ion beam (FIB) source. This Focused Ion Beam can be used in applications where milling, imaging and deposition at the nanoscale needs to be done with increasing demands on control and resolution. The generation of the ion beam done in three stage principle. The first stage is the generation of the atomic beam and this is the subject of this work. The following stages first transversely cool and compress the atomic beam by using laser cooling techniques and then ionize and accelerate the atoms to form the ion beam. The generation of the atomic beam is done using a Knudsen cell; an effusive oven containing a vapor of rubidium atoms. The pressure difference between the vapor pressure in the oven and the vacuum outside the oven generates a flow of atoms from the oven to the vacuum. Only atoms that have a low transverse velocity can be captured by the laser cooling stage and will attribute to the ion beam. Therefore it is important to minimize the divergence in the beam and to this extent a collimating tube is used to connect the effusive oven to the vacuum system. The collimating tube minimizes beam divergence and compared to other collimating mechanisms it reduces the amount of rubidium loss, therefore greatly increasing the lifetime of the system.In order to measure the transverse velocity distribution, the transverse beam profile and the total flux, Laser-Induced Fluorescence measurements have been performed. These measurements show that the source generates an atomic beam with a particle flux ranging from 107 s-1 at a source temperature of 60 ºC to 1010 s-1 at a source temperature of 160 ºC. The flux is lower than predicted by theory and the transverse velocity distribution is broader than predicted by theory. However, the particle flux is stable within 1% and the installation of an active temperature controller promises to improve this stability even further.

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A new type of ultra-cold ion source is under development which employs transverse laser cooling and compression of a thermal atomic rubidium beam followed by photo-ionization. The resulting ultra-cold plasma is focused to a nanometer-sized spot using an existing Focused Ion Beam column and this spot can be used for the fabrication of nano-structures. Simulations of a 10 cm long laser-cooling stage and of disorder-induced heating of the resulting ion beam, predict an achievable brightness for87Rb+ of order 107 A/m2 sr eV at an longitudinal energy spread of less than 1 eV and a current of tens of pA, which is substantially better than conventional ion sources. Experimental realization of the compact ion source has recently started with the development of an efficient high-flux atom source and a 2D laser cooler. Progress on these items will be reported.

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A new type of high-brightness ion source is under development which employs transverse laser cooling and compression of a thermal atomic rubidium beam, followed by in-field photo-ionization. When attached to a focusing column, this Focused Ion Beam (FIB) has the advantage of supplying a higher current in a smaller spot compared to conventional LMIS-based FIBs, thus increasing both the resolution and the speed of the FIB. Furthermore, different types of ion species can be used, broadening the range of applications of the FIB. Simulations using a 10 cm long laser cooling and compression stage and a realistic ionization and acceleration structure, predict an achievable brightness for 87 Rb + of order 10 7 A/m 2 sr eV at an energy spread of less than 1 eV and a current of tens of pA. This would lead to a spot size below 5 nm. Simulations and modeling on the ionization process have led to a better understanding of stochastic heating. Experimental realization of the compact ion source has recently started with the development of an efficient high-flux atom source and a 2D laser cooler and compressor. Progress on simulations and experimental results will be reported.

•Jan 1, 2013•0 citations

Performance predictions for a laser-intensified thermal beam for use in high-resolution focused-ion-beam instruments

Steinar H. W. Wouters, G. ten Haaf, Remy Notermans +4 more

Photoionization of a laser-cooled and compressed atomic beam from a high-flux thermal source can be used to create a high-brightness ion beam for use in focused-ion-beam instruments. Here we show using calculations and Doppler cooling simulations that an atomic rubidium beam with an equivalent brightness of $2.1\ifmmode\times\else\texttimes\fi{}{10}^{7} \mathrm{A}/(\mathrm{m}{}^{2} \mathrm{sr} \mathrm{eV})$ can be created using a compact 5 cm long two-dimensional magneto-optical compressor. If this can be conserved during the photoionization process, this leads to an ion beam brightness an order of magnitude higher than produced by a liquid metal ion source. The source is also capable of producing a flux of $6.2\ifmmode\times\else\texttimes\fi{}{10}^{9} \mathrm{s}{}^{\ensuremath{-}1}$ that results in a substantial beam current of 1 nA once fully ionized.

arXiv:1410.4350•Physical Review A•Dec 15, 2014•17 citations
In this paper we discuss the design and performance of a collimated Knudsen source which has the benefit of a simple design over recirculating sources. Measurements of the flux, transverse velocity distribution and brightness at different temperatures were conducted to evaluate the performance. The scaling of the flux and brightness with the source temperature follow the theoretical predictions. The transverse velocity distribution in the transparent operation regime also agrees with the simulated data. The source was found able to produce a flux of 101410^{14}1014 s−1^{-1}−1 at a temperature of 433 K. Furthermore the transverse reduced brightness of an ion beam with equal properties as the atomic beam reads 1.7×1021.7 \times 10^21.7×102 A/(m2{}^22 sr eV) which is sufficient for our goal: the creation of an ultra-cold ion beam by ionization of a laser-cooled and compressed atomic rubidium beam.
In this paper we discuss the design and performance of a collimated Knudsen source which has the benefit of a simple design over recirculating sources. Measurements of the flux, transverse velocity distribution and brightness at different temperatures were conducted to evaluate the performance. The scaling of the flux and brightness with the source temperature follow the theoretical predictions. The transverse velocity distribution in the transparent operation regime also agrees with the simulated data. The source was found able to produce a flux of 101410^{14}1014 s−1^{-1}−1 at a temperature of 433 K. Furthermore the transverse reduced brightness of an ion beam with equal properties as the atomic beam reads 1.7×1021.7 \times 10^21.7×102 A/(m2{}^22 sr eV) which is sufficient for our goal: the creation of an ultra-cold ion beam by ionization of a laser-cooled and compressed atomic rubidium beam.
In this paper, the design and performance of a collimated Knudsen source, which has the benefit of a simple design over recirculating sources, is discussed. Measurements of the flux, transverse velocity distribution, and brightness of the resulting rubidium beam at different source temperatures were conducted to evaluate the performance. The scaling of the flux and brightness with the source temperature follows the theoretical predictions. The transverse velocity distribution in the transparent operation regime also agrees with the simulated data. The source was tested up to a temperature of 433 K and was able to produce a flux in excess of 10(13) s(-1).
In the ultracold FIB project a high brightness ion beam is developed for usage in a focused ion beam (FIB) source. This Focused Ion Beam can be used in applications where milling, imaging and deposition at the nanoscale needs to be done with increasing demands on control and resolution. The generation of the ion beam done in three stage principle. The first stage is the generation of the atomic beam and this is the subject of this work. The following stages first transversely cool and compress the atomic beam by using laser cooling techniques and then ionize and accelerate the atoms to form the ion beam. The generation of the atomic beam is done using a Knudsen cell; an effusive oven containing a vapor of rubidium atoms. The pressure difference between the vapor pressure in the oven and the vacuum outside the oven generates a flow of atoms from the oven to the vacuum. Only atoms that have a low transverse velocity can be captured by the laser cooling stage and will attribute to the ion beam. Therefore it is important to minimize the divergence in the beam and to this extent a collimating tube is used to connect the effusive oven to the vacuum system. The collimating tube minimizes beam divergence and compared to other collimating mechanisms it reduces the amount of rubidium loss, therefore greatly increasing the lifetime of the system.In order to measure the transverse velocity distribution, the transverse beam profile and the total flux, Laser-Induced Fluorescence measurements have been performed. These measurements show that the source generates an atomic beam with a particle flux ranging from 107 s-1 at a source temperature of 60 ºC to 1010 s-1 at a source temperature of 160 ºC. The flux is lower than predicted by theory and the transverse velocity distribution is broader than predicted by theory. However, the particle flux is stable within 1% and the installation of an active temperature controller promises to improve this stability even further. In the ultracold FIB project a high brightness ion beam is developed for usage in a focused ion beam (FIB) source. This Focused Ion Beam can be used in applications where milling, imaging and deposition at the nanoscale needs to be done with increasing demands on control and resolution. The generation of the ion beam done in three stage principle. The first stage is the generation of the atomic beam and this is the subject of this work. The following stages first transversely cool and compress the atomic beam by using laser cooling techniques and then ionize and accelerate the atoms to form the ion beam. The generation of the atomic beam is done using a Knudsen cell; an effusive oven containing a vapor of rubidium atoms. The pressure difference between the vapor pressure in the oven and the vacuum outside the oven generates a flow of atoms from the oven to the vacuum. Only atoms that have a low transverse velocity can be captured by the laser cooling stage and will attribute to the ion beam. Therefore it is important to minimize the divergence in the beam and to this extent a collimating tube is used to connect the effusive oven to the vacuum system. The collimating tube minimizes beam divergence and compared to other collimating mechanisms it reduces the amount of rubidium loss, therefore greatly increasing the lifetime of the system.In order to measure the transverse velocity distribution, the transverse beam profile and the total flux, Laser-Induced Fluorescence measurements have been performed. These measurements show that the source generates an atomic beam with a particle flux ranging from 107 s-1 at a source temperature of 60 ºC to 1010 s-1 at a source temperature of 160 ºC. The flux is lower than predicted by theory and the transverse velocity distribution is broader than predicted by theory. However, the particle flux is stable within 1% and the installation of an active temperature controller promises to improve this stability even further.
A new type of ultra-cold ion source is under development which employs transverse laser cooling and compression of a thermal atomic rubidium beam followed by photo-ionization. The resulting ultra-cold plasma is focused to a nanometer-sized spot using an existing Focused Ion Beam column and this spot can be used for the fabrication of nano-structures. Simulations of a 10 cm long laser-cooling stage and of disorder-induced heating of the resulting ion beam, predict an achievable brightness for87Rb+ of order 107 A/m2 sr eV at an longitudinal energy spread of less than 1 eV and a current of tens of pA, which is substantially better than conventional ion sources. Experimental realization of the compact ion source has recently started with the development of an efficient high-flux atom source and a 2D laser cooler. Progress on these items will be reported.
A new type of high-brightness ion source is under development which employs transverse laser cooling and compression of a thermal atomic rubidium beam, followed by in-field photo-ionization. When attached to a focusing column, this Focused Ion Beam (FIB) has the advantage of supplying a higher current in a smaller spot compared to conventional LMIS-based FIBs, thus increasing both the resolution and the speed of the FIB. Furthermore, different types of ion species can be used, broadening the range of applications of the FIB. Simulations using a 10 cm long laser cooling and compression stage and a realistic ionization and acceleration structure, predict an achievable brightness for 87 Rb + of order 10 7 A/m 2 sr eV at an energy spread of less than 1 eV and a current of tens of pA. This would lead to a spot size below 5 nm. Simulations and modeling on the ionization process have led to a better understanding of stochastic heating. Experimental realization of the compact ion source has recently started with the development of an efficient high-flux atom source and a 2D laser cooler and compressor. Progress on simulations and experimental results will be reported.
Photoionization of a laser-cooled and compressed atomic beam from a high-flux thermal source can be used to create a high-brightness ion beam for use in focused-ion-beam instruments. Here we show using calculations and Doppler cooling simulations that an atomic rubidium beam with an equivalent brightness of $2.1\ifmmode\times\else\texttimes\fi{}{10}^{7} \mathrm{A}/(\mathrm{m}{}^{2} \mathrm{sr} \mathrm{eV})$ can be created using a compact 5 cm long two-dimensional magneto-optical compressor. If this can be conserved during the photoionization process, this leads to an ion beam brightness an order of magnitude higher than produced by a liquid metal ion source. The source is also capable of producing a flux of $6.2\ifmmode\times\else\texttimes\fi{}{10}^{9} \mathrm{s}{}^{\ensuremath{-}1}$ that results in a substantial beam current of 1 nA once fully ionized.