Rydberg atoms Tobias Thiele References • T. Gallagher: Rydberg atoms Content • Part 1: Rydberg atoms • Part 2: A typical beam experiment Introduction – What is „Rydberg“? • Rydberg atoms are (any) atoms in state with high principal quantum number n. Introduction – What is „Rydberg“? • Rydberg atoms are (any) atoms in state with high principal quantum number n. • Rydberg atoms are (any) atoms with exaggerated properties Introduction – What is „Rydberg“? • Rydberg atoms are (any) atoms in state with high principal quantum number n. • Rydberg atoms are (any) atoms with exaggerated properties equivalent! Introduction – How was it found? • In 1885: Balmer series: – Visible absorption wavelengths of H: bn 2 2 n 4 – Other series discovered by Lyman, Brackett, Paschen, ... – Summarized by Johannes Rydberg: Introduction – How was it found? • In 1885: Balmer series: – Visible absorption wavelengths of H: bn 2 2 n 4 – Other series discovered by Lyman, Brackett, Paschen, ... – Summarized by Johannes Rydberg: Introduction – How was it found? • In 1885: Balmer series: – Visible absorption wavelengths of H: bn 2 2 n 4 – Other series discovered by Lyman, Brackett, Paschen, ... – Summarized by Johannes Rydberg: ~ ~ Ry n2 Introduction – Generalization • In 1885: Balmer series: – Visible absorption wavelengths of H: bn 2 2 n 4 – Other series discovered by Lyman, Brackett, Paschen, ... – Quantum Defect was found for other atoms: ~ ~ Ry (n l ) 2 Introduction – Rydberg formula? • Energy follows Rydberg formula: E E hRy (n l ) 2 Introduction – Rydberg formula? • Energy follows Rydberg formula: E E hRy 13.6 eV (n l ) 2 Introduction – Hydrogen? • Energy follows Rydberg formula: 0 E E 13.6 eV hRy (n l ) 2 0 Energy 0 hRy n2 Quantum Defect? • Energy follows Rydberg formula: E E hRy (n l ) 2 Quantum Defect Energy 0 Rydberg Atom Theory e • Rydberg Atom A • Almost like Hydrogen – Core with one positive charge – One electron • What is the difference? Rydberg Atom Theory e • Rydberg Atom A • Almost like Hydrogen – Core with one positive charge – One electron • What is the difference? Rydberg Atom Theory e • Rydberg Atom A • Almost like Hydrogen – Core with one positive charge – One electron • What is the difference? Rydberg Atom Theory e • Rydberg Atom A • Almost like Hydrogen – Core with one positive charge – One electron • What is the difference? – No difference in angular momentum states Radial parts-Interesting regions W 1 V (r ) r 0 r Radial parts-Interesting regions W 1 V (r ) Vcore (r ) r 0 1 V (r ) r r Radial parts-Interesting regions W r r0 Ion core 1 V (r ) Vcore (r ) r 0 1 V (r ) r r Radial parts-Interesting regions W r r0 Ion core 1 V (r ) Vcore (r ) r 0 1 V (r ) r r Interesting Region For Rydberg Atoms Radial parts-Interesting regions W r r0 Ion core 1 V (r ) Vcore (r ) r 1 V (r ) r 0 r H Radial parts-Interesting regions W r r0 Ion core 1 V (r ) Vcore (r ) r 1 V (r ) r 0 r H nH Radial parts-Interesting regions W r r0 Ion core 1 V (r ) r 1 V (r ) Vcore (r ) r 0 r δl H nH (Helium) Energy Structure • l usually measured – Only large for low l (s,p,d,f) • He level structure • is big for s,p 1 W 2(n l ) 2 (Helium) Energy Structure • l usually measured – Only large for low l (s,p,d,f) • He level structure • is big for s,p 1 W 2(n l ) 2 (Helium) Energy Structure • l usually measured – Only large for low l (s,p,d,f) • He level structure • l is big for s,p 1 W 2(n l ) 2 (Helium) Energy Structure • l usually measured – Only large for low l (s,p,d,f) • He level structure • l is big for s,p Excentric orbits penetrate into core. Large deviation from Coulomb. Large phase shift-> large quantum defect 1 W 2(n l ) 2 (Helium) Energy Structure • l usually measured – Only large for low l (s,p,d,f) • He level structure • l is big for s,p dW 1 • dn (n l )3 1 W 2(n l ) 2 Electric Dipole Moment • Electron most of the time far away from core – Strong electric dipole: – Proportional to transition matrix element W dW 1 1 3 2(n l ) 2 dn (n l ) Electric Dipole Moment • Electron most of the time far away from core – Strong electric dipole: d er – Proportional to transition matrix element W dW 1 1 3 2(n l ) 2 dn (n l ) Electric Dipole Moment • Electron most of the time far away from core – Strong electric dipole: d er – Proportional to transition matrix element f d i e f r i e f r cos( ) i W dW 1 1 3 2(n l ) 2 dn (n l ) Electric Dipole Moment • Electron most of the time far away from core – Strong electric dipole: d er – Proportional to transition matrix element f d i e f r i e f r cos( ) i • We find electric Dipole Moment – f d i r l 1 cos( ) l n 2 • Cross Section: dW 1 1 W 3 2(n l ) 2 dn (n l ) d a0n 2 Electric Dipole Moment • Electron most of the time far away from core – Strong electric dipole: d er – Proportional to transition matrix element f d i e f r i e f r cos( ) i • We find electric Dipole Moment – f d i r l 1 cos( ) l n 2 4 r n • Cross Section: 2 dW 1 1 W 3 2(n l ) 2 dn (n l ) d a0n 2 n 4 Stark Effect H H 0 dF E • For non-Hydrogenic Atom (e.g. Helium) – „Exact“ solution by numeric diagonalization of f H i f H 0 i f d i F in undisturbed (standard) basis ( n~ ,l,m) dW 1 1 W 3 2(n l ) 2 dn (n l ) d a0n 2 n 4 Stark Effect H H 0 dF E • For non-Hydrogenic Atom (e.g. Helium) – „Exact“ solution by numeric diagonalization of f H i f H 0 i f d i F in undisturbed (standard) basis ( n~ ,l,m) 1 W 2(n l ) 2 dW 1 1 W 3 2(n l ) 2 dn (n l ) d a0n 2 n 4 Stark Effect H H 0 dF E • For non-Hydrogenic Atom (e.g. Helium) – „Exact“ solution by numeric diagonalization of f H i f H 0 i f d i F in undisturbed (standard) basis ( n~ ,l,m) 1 W 2(n l ) 2 dW 1 1 W 3 2(n l ) 2 dn (n l ) d a0n 2 n 4 Numerov Stark Map Hydrogen n=13 n=12 n=11 Stark Map Hydrogen n=13 Levels degenerate n=12 n=11 Stark Map Hydrogen n=13 k=-11 blue n=12 k=11 red n=11 Stark Map Hydrogen n=13 Levels degenerate n=12 Cross perfect Runge-Lenz vector conserved n=11 Stark Map Helium n=13 n=12 n=11 Stark Map Helium n=13 Levels not degenerate n=12 n=11 Stark Map Helium n=13 k=-11 blue n=12 k=11 red n=11 Stark Map Helium n=13 k=-11 blue n=12 s-type k=11 red n=11 Stark Map Helium n=13 Levels degenerate n=12 Do not cross! No coulomb-potential n=11 Stark Map Helium Inglis-Teller Limit n-5 n=13 n=12 n=11 Hydrogen Atom in an electric Field • Rydberg Atoms very sensitive to electric fields – Solve: H H 0 dF E in parabolic coordinates • Energy-Field dependence: Perturbation-Theory 1 3 F 4 2 2 2 5 W 2 F (nn1 n ) n n 17 n 3 ( n n ) 9 m 19 O ( n ) 1 n2 2 1 22 n 1 n 2n 2 16 k k Hydrogen Atom in an electric Field • When do Rydberg atoms ionize? – No field applied – Electric Field applied – Classical ionization: – Valid only for • Non-H atoms if F is Increased slowly dW 1 1 W 3 2(n l ) 2 dn (n l ) d a0n 2 n 4 FIT n 5 Hydrogen Atom in an electric Field • When do Rydberg atoms ionize? – No field applied – Electric Field applied – Classical ionization: – Valid only for • Non-H atoms if F is Increased slowly dW 1 1 W 3 2(n l ) 2 dn (n l ) d a0n 2 n 4 FIT n 5 Hydrogen Atom in an electric Field • When do Rydberg atoms ionize? – No field applied – Electric Field applied – Classical ionization: 1 V Fz r W2 1 Fcl 4 16n 4 Fcl 1 16n 4 – Valid only for • Non-H atoms if F is Increased slowly dW 1 1 W 3 2(n l ) 2 dn (n l ) 4 d a0n 2 n 4 FIT n 5 Fcl 116 n Hydrogen Atom in an electric Field • When do Rydberg atoms ionize? – No field applied – Electric Field applied – Classical ionization: 1 V Fz r W2 1 Fcl 4 16n 4 Fcl 1 16n 4 – Valid only for • Non-H atoms if F is Increased slowly dW 1 1 W 3 2(n l ) 2 dn (n l ) 4 d a0n 2 n 4 FIT n 5 Fcl 116 n Hydrogen Atom in an electric Field • When do Rydberg atoms ionize? – No field applied – Electric Field applied – Quasi-Classical ioniz.: Fcl 1 16n 4 Z 2 m 2 1 F V ( ) 2 2 4 4 m 0 W2 F 4Z 2 dW 1 1 W 3 2(n l ) 2 dn (n l ) 4 d a0n 2 n 4 FIT n 5 Fcl 116 n Hydrogen Atom in an electric Field • When do Rydberg atoms ionize? – No field applied – Electric Field applied – Quasi-Classical ioniz.: Z 2 m 2 1 F V ( ) 2 2 4 4 1 m 0 W 2 4 red F 9n 4Z 2 dW 1 1 W 3 2(n l ) 2 dn (n l ) Fcl 1 16n 4 Fr 1 9n 4 4 d a0n 2 n 4 FIT n 5 Fcl 116 n Hydrogen Atom in an electric Field • When do Rydberg atoms ionize? – No field applied – Electric Field applied – Quasi-Classical ioniz.: Z 2 m 2 1 F V ( ) 2 2 4 4 1 2 red 4 W 9n F 4Z 2 2 blue 9n 4 dW 1 1 W 3 2(n l ) 2 dn (n l ) Fb 2 Fr 1 9n 4 1 Fcl 16n 4 9n 4 4 d a0n 2 n 4 FIT n 5 Fcl 116 n Hydrogen Atom in an electric Field Blue states Red states classic Inglis-Teller Lifetime • From Fermis golden rule – Einstein A coefficient for two states n, l n, l An,l ,n,l 4e 2n3,l ,n,l max( l , l ) nl r nl 3 3c 2l 1 2 – Lifetime dW 1 1 W 3 2(n l ) 2 dn (n l ) 4 d a0n 2 n 4 FIT n 5 Fcl 116 n Lifetime • From Fermis golden rule – Einstein A coefficient for two states n, l n, l An,l ,n,l 4e 2n3,l ,n,l max( l , l ) nl r nl 3 3c 2l 1 – Lifetime n,l dW 1 1 W 3 2(n l ) 2 dn (n l ) An,l ,n,l n , l n ,l 2 1 4 d a0n 2 n 4 FIT n 5 Fcl 116 n Lifetime • From Fermis golden rule – Einstein A coefficient for two states n, l n, l An,l ,n,l 4e 2n3,l ,n,l max( l , l ) nl r nl 3 3c 2l 1 – Lifetime n,l dW 1 1 W 3 2(n l ) 2 dn (n l ) An,l ,n,l n , l n ,l 2 1 4 d a0n 2 n 4 FIT n 5 Fcl 116 n Lifetime • From Fermis golden rule – Einstein A coefficient for two states n, l n, l An,l ,n,l 4e 2n3,l ,n,l max( l , l ) nl r nl 3 3c 2l 1 – Lifetime n,l dW 1 1 W 3 2(n l ) 2 dn (n l ) An,l ,n,l n , l n ,l 2 1 3 For l0: n 2 Overlap of WF 4 n,0 n3 d a0n 2 n 4 FIT n 5 Fcl 116 n Lifetime • From Fermis golden rule – Einstein A coefficient for two states n, l n, l An,l ,n,l 4e 2n3,l ,n,l max( l , l ) nl r nl 3 3c 2l 1 – Lifetime n,l An,l ,n,l n , l n ,l 2 1 For ln: n 2 Overlap of WF For ln: n 3 Overlap of WF dW 1 1 W 3 2(n l ) 2 dn (n l ) 4 d a0n 2 n 4 FIT n 5 Fcl 116 n n,l n3 , n5 Lifetime 4e 2 An,l ,n,l 3 n , l , n , l 3 3c Stark State 60 p (n,l ) small State Scaling max( l , l ) nl r nl 2l 1 n Lifetime dW 1 1 W 3 2(n l ) 2 dn (n l ) 7.2 ms n ,l Circular state 60 l=59 m=59 An,l ,n,l n , l n ,l (n, l ) (n 1, l 1) 3 (overlap of n 2 3 n 2) 5 r n2 70 ms 1 Statistical mixture n 4.5 ms 4 n,l n 3 , n5 d a0n 2 n 4 FIT n 5 Fcl 116 n Part 2- Generation of Rydberg atoms • Typical Experiments: – Beam experiments – (ultra) cold atoms – Vapor cells ETH physics Rydberg experiment Creation of a cold supersonic beam of Helium. Speed: 1700m/s, pulsed: 25Hz, temperature atoms=100mK ETH physics Rydberg experiment Excite electrons to the 2s-state, (to overcome very strong binding energy in the xuv range) by means of a discharge – like a lightning. ETH physics Rydberg experiment Actual experiment consists of 5 electrodes. Between the first 2 the atoms get excited to Rydberg states up to n=inf with a dye laser. Dye/Yag laser system Dye/Yag laser system Experiment Dye/Yag laser system Experiment Nd:Yag laser (600 mJ/pp, 10 ns pulse length, Power -> 10ns of MW!!) Provides energy for dye laser Dye/Yag laser system Dye laser with DCM dye: Dye is excited by Yag and fluoresces. A cavity creates light with 624 nm wavelength. This is then frequency doubled to 312 nm. Experiment Nd:Yag laser (600 mJ/pp, 10 ns pulse length, Power -> 10ns of MW!!) Provides energy for dye laser Dye laser Nd:Yag pump laser cuvette Frequency doubling DCM dye ETH physics Rydberg experiment Detection: 1.2 kV/cm electric field applied in 10 ns. Rydberg atoms ionize and electrons are Detected at the MCP detector (single particle multiplier) . Results TOF 100ns Results TOF 100ns Inglis-Teller limit Results TOF 100ns Adiabatic Ionizationrate ~ 70% (fitted) 1250V cm 16 nd F0 1 4 Results TOF 100ns Adiabatic Ionizationrate ~ 70% (fitted) Pure diabatic Ionizationrate: exp( t ) 1250V cm 16 nd F0 1 4 1250V cm nd F0 9 2 1 4 Results TOF 100ns Adiabatic Ionizationrate ~ 70% (fitted) Pure diabatic Ionizationsaturation rate: exp( t ) 1250V cm 16 nd F0 1 4 1250V cm nd F0 9 2 1 4 r n3 From ground state 2 Results TOF 15ms lifetime n3 1250V cm 16 nd F0 1 4 1250V cm nd F0 9 2 1 4 r n3 From ground state 2