Direct Observation of Rydberg–Rydberg Transitions in Calcium Atoms K. Kuyanov-Prozument, A.P. Colombo, Y. Zhou, G.B. Park, V.S. Petrović, and R.W. Field Department of Chemistry Massachusetts Institute of Technology The Ohio State University International Symposium on Molecular Spectroscopy 22 June 2010

 We extended Brooks Pate’s CP-FTMW to mm- waves.  Adapt CPmmW for Rydberg–Rydberg transitions:  Polarize with (chirped, broadband) mm- waves.  Detect the free induction decay. What I mean by “direct”

Challenges for Rydberg–Rydberg Transitions  Δn * ≈ 1 has transition dipole moments ~5,000 Debye at n * = 30 – 40.  ~100 pW over 1 cm 2 will saturate a transition in 1 μs.  (We have 30 mW.)  Collective effects preclude high number density. volume  We enlarged the volume of the interaction region.

Exciting Calcium Atoms 3p64s5p3p64s5p 3p64s23p64s2 1 P° intermediate state 1 S ground state 1 S or 1 D initial Rydberg state 1 P° or 1 F° 272 nm 800 nm 70 – 84 GHz 36,700 cm −1 ~ 12,500 cm −1 ~ 2.5 cm −1 n* ≈ 30 – 40 |Δn*| < 1

mm-wave Chamber Ionization Chamber 12 GHz Scope 10 MHz Standard 3.96 GHz PDRO 4.2 GS/s AWG 10.7 GHz PDRO Gunn Lock Box Delay Generator A Delay Generator B 1 GHz Scope Gas Nozzle Driver Extraction Pulse Pulse Timings Gas pulse Ablation laser pulse mm-wave pulse Extraction pulse Dye laser pulses Ablation YAG LaserExcitation YAG Laser Dye Laser x2 Spatial Filter MCP Einsel tube 1500V + Extraction pulse 1500V 1200V mm-wave Chamber (top view) Ionization Chamber (top view) Ionization Chamber (side view) Gunn Oscillator x4x2 Variable Attenuator Spatial Filter OR

mm-wave Chamber Ionization Chamber 12 GHz Scope 10 MHz Standard 3.96 GHz PDRO 4.2 GS/s AWG 10.7 GHz PDRO Gunn Lock Box Delay Generator A Delay Generator B 1 GHz Scope Gas Nozzle Driver Extraction Pulse Pulse Timings Gas pulse Ablation laser pulse mm-wave pulse Extraction pulse Dye laser pulses Ablation YAG LaserExcitation YAG Laser Dye Laser x2 Spatial Filter MCP Einsel tube 1500V + Extraction pulse 1500V 1200V mm-wave Chamber (top view) Ionization Chamber (top view) Ionization Chamber (side view) Gunn Oscillator x4x2 Variable Attenuator Spatial Filter OR

A Signal in the Time Domain

33.67s 34.13p 29.80d 30.12p 40.88f 41.73d 37.13p 37.78d Signals in the Frequency Domain Observed lines (41.73d–40.88f excluded) agree with Gentile et al., Phys. Rev. A 42, 440 (1990).

FID Within a Chirp

π/2π 20 ns, 6 V/m10 ns, 6 V/m 2.2 μs Photon Echo Time/μs

Molecules  Goal: “Pure Electronic Spectroscopy” on core-nonpenetrating states.  Characterize multipole moments and polarizabilities of ion core.  CPmmW spectroscopy has the Resolution we need (10 3 times better than pulsed dye lasers). Survey capability we like.

Acknowledgments  Brooks Pate  Justin Neill  Adam Steeves  NSF, DHS, DOE  Tektronix

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The Problem(s) with Molecules  Fast predissociation (and autoionization)  Complementary approaches Populate high-ℓ states  Coherent, multiphoton excitations  Stark mixing Separate chirp from FID  Polarization spectroscopy

Advantages of Large Transition Dipole Moments  Can polarize a transition in ~10 ns.  No penalty for using full oscilloscope bandwidth (10 GHz), with resolution better than 1 MHz.  More of the (most intense) FID.  Exploit fast/strong polarization.

Rabi Oscillations π/2π 3π/2 2π2π Time/μs

Which way is up? 40.88f 41.73d 33.67s 34.13p Time/μs Time/ns

mm-wave Chamber Ionization Chamber 12 GHz Scope 10 MHz Standard 3.96 GHz PDRO 4.2 GS/s AWG 10.7 GHz PDRO Gunn Lock Box Delay Generator A Delay Generator B 1 GHz Scope Gas Nozzle Driver Extraction Pulse Pulse Timings Gas pulse Ablation laser pulse mm-wave pulse Extraction pulse Dye laser pulses Ablation YAG LaserExcitation YAG Laser Dye Laser x2 Spatial Filter MCP Einsel tube 1500V + Extraction pulse 1500V 1200V mm-wave Chamber (top view) Ionization Chamber (top view) Ionization Chamber (side view) Gunn Oscillator x4x2 Variable Attenuator Spatial Filter OR

Time Series of Echos

Phase-Lock Loop for Gunn Oscillator Gunn Oscillator Variable Attenuator Directional Coupler Out to mixer Subharmonic mixer Diplexer 10 MHz Rb Clock PDRO ~2−18 GHz (or synthesizer) Lock Box Difference Freq.