An experimental demonstration of a fast atomic line filter/field ionization detector (FALF/FID) is presented. The FALF/FID detects incoming signal photons by resonant absorption in an atomic vapor cell containing a strong electric field. Excited atoms are electric-field ionized after further excitation to a Stark-shifted Rydberg level by a pump laser tuned to a resonance in the ionization spectrum, providing an observed enhancement in the ionization rate of ten times over the continuum ionization threshold. Preliminary measurements of time response (<10 nsec) and quantum efficiency (>25%) indicate that with optimization the FALF/FID will provide high quantum efficiency, fast time response, and narrow-linewidth detection.
An experimental demonstration of a fast atomic line filter/field ionization detector (FALF/FID) is presented. The FALF/FID detects incoming signal photons by resonant absorption in an atomic vapor cell containing a strong electric field. Excited atoms are electric-field ionized after further excitation to a Stark-shifted Rydberg level by a pump laser tuned to a resonance in the ionization spectrum, providing an observed enhancement in the ionization rate of ten times over the continuum ionization threshold. Preliminary measurements of time response (<10 nsec) and quantum efficiency (>25%) indicate that with optimization the FALF/FID will provide high quantum efficiency, fast time response, and narrow-linewidth detection.
When optical signals are embedded in background noise, narrowband optical filters are needed for receivers to achieve quantum limited performance. Such is typically the case with daytime optical communications and lidar. Narrowband filtered detectors. with acceptance bands of just a few picometers (pm) and high out of band rejection are well suited for these applications. The main thrust of this program has been the development of two means for narrowband detection: the Fast Atomic Line Filter/ Field Ion Detector (FALF/FID) and the Faraday magneto-optic filter. The FALF/FIDs transduce optical radiation within a narrow band directly into electrical signals. They are laser pumped filters based on the spectroscopy of atomic vapors. We designed, built and tested an infrared FALF/FID with an rise time of under 10 ns and a quantum efficiency of >25%. Faraday filters are imaging magneto-optic filters with passbands of a few pm. Faraday filters with passbands in the visable and the near infra-red were constructed and tested. Transmission spectra were measured, and found to agree closely with theoretical predictions. Both of these narrowband detection schemes must be used in conjunction with a tuned narrowband laser source. We developed a frequency locked alexandrite laser designed to match the acceptance band of a rubidium based filter. Finally, a preliminary demonstration of a laser interrogator using a tuned infrared diode laser in conjunction with a filtered receiver was demonstrated. Atomic line filter, Alkali metal vapor, Faraday filter, Active optical filter, Laser pumped filter, Magneto-optic filter, Laser communications.
We present a Rydberg-Atom electric field sensor optimized to detect signals at sub-100 MHz carrier frequencies. The sensing setup employs a sapphire vapor cell that allows for detection of signals below 100 MHz-typical vapor cells made of glass or quartz demonstrate strong screening of radio frequency (RF) signals in this frequency regime. Applied signals are detected by observing AC Stark shifts in the atomic vapor energy levels. As a test case for the commercial utility of this receiver, we perform our tests at several carrier frequencies in the Industrial, Scientific, and Medical (ISM) band. At each carrier frequency, we report sensitivity, minimum detectable field, and detectable electric-field dynamic range. We also present a routine for optimizing off-resonant signal detection by tuning experimental parameters such as Rydberg coupler laser detuning and RF local oscillator strength. This Python-based optimization routine, which can be used at any off-resonant carrier frequency, is shared on GitHub for others to use in their own investigations.
The high polarizability of Rydberg atoms enables the multi-parameters measurement of electromagnetic fields. In this paper, we report on an atomic antenna based on Rydberg atoms in a room temperature vapor cell. The EIT is a destructive interference spectroscopy with a narrow linewidth and can be used to detect small electric fields through Autler-Townes splitting or Stark shifts. In our experiments, we employ cascade-type two-photon excitation electromagnetically induced transparency (EIT) spectroscopy to measure the shift of the Rydberg energy level. We introduce a low-frequency electric field (~kHz frequency) using a built-in electrode technique in the cesium cell. The interaction between the Rydberg atom and electric field induces the Stark shifts, where the amplitude of the electric field is converted into corresponding two-photon detuning by the EIT effect. Furthermore, the amplitude of the low-frequency electric field is converted into an intensity signal of EIT probe beam. Under weak field conditions, it is an approximate linear relationship between EIT transmission signal and input electric field amplitude, enabling measurement of waveform, amplitude, and frequency. We have demonstrated optical measurements of low-frequency electric field using Rydberg atoms. By increasing the power of probe beam and coupling beam, the EIT can increase the response bandwidth from ~MHz to hundreds of MHz. This provides a scalable approach for measuring high-frequency electric fields.
The coherent control of atomic energy level population is important for several areas physics and engineering including fluorescent spectroscopy, resonantly enhanced multiphoton ionization, harmonic generation, remote sensing and lasing. At low intensities where the Stark shift can be neglected, coherent control mechanisms usually exploit resonances created from stationary energy states dressed by integer multiples of the photon energy. However, in the strong field limit where large laser pulse intensities lead to significant Stark shifts, the resonant conditions are dynamic both in time and space and will likely not be satisfied for the entire laser pulse or beam.\n\nIn this research, we experimentally and theoretically demonstrate coherent control of atomic energy level population in sodium vapor as well as the selective excitation of sodium Rydberg levels using high intensity laser pulses. We also make a direct measurement of the ponderomotive shift of the continuum. While techniques based on resonance interferences and rapid adiabatic passage have been introduced for selective excitation, the conditions that must be satisfied for these phenomena can be hampered by short femtosecond pulse durations and large Stark shifts. In contrast, a technique referred to here as Resonance Sampling, uses the AC Stark shifts to selectively induce Freeman resonances and is resilient to changes in the spectral phase. Freeman resonances established in this way can result in population inversion of the excited state, and may lead to new lasing mediums and remote sensing applications.\n\n\nIn this research, we experimentally and theoretically demonstrate coherent control of atomic energy level population in sodium vapor as well as the selective excitation of sodium Rydberg levels using high intensity laser pulses. While techniques based on resonance interferences and rapid adiabatic passage have been introduced for selective excitation, the conditions that must be satisfied for these phenomena can be hampered by short femtosecond pulse durations and large Stark shifts. In contrast, a technique referred to here as Resonance Sampling, uses the AC Stark shifts to selectively induce Freeman resonances and is resilient to changes in the spectral phase. Freeman resonances established in this way can result in population inversion of the excited state, and may lead to new lasing mediums and remote sensing applications.
The Stark splitting of the second excited level of atomic hydrogen (with principal quantum number n=3) has been measured by pulsed laser spectroscopy in order to determine small electric fields by optical means. Doppler-free excitation with two counterpropagating laser beams at 205nm allows us to measure the n=3 Stark spectra either by an optogalvanic signal after ionization by a third laser photon or by detection of the Balmer-$\ensuremath{\alpha}$ fluorescence photons emitted by the excited atoms. Three different cases of laser polarization have been investigated in order to evaluate the possibilities and limitations of this one-step laser excitation method for electric field determination, especially at field strengths below 200V∕cm. The method provides the best field sensitivity achieved with lower excited levels that can be reached directly by two-photon absorption from the ground state (in contrast to the more sensitive Rydberg levels). For this purpose, an advanced tunable pulsed uv laser with narrow bandwidth almost at the Fourier limit has been used. The high spectral resolution allowed us to deduce electric field strengths as small as 50V∕cm from the frequency shift between two selected isolated Stark components. As a main advantage, this simple analysis of the measured spectra does not rely on knowledge of the line intensities which may be strongly affected by the measuring conditions.
The outer electron of a Rydberg atom is so weakly bound to the atomic core that a relatively small electric field may cause the electron to be stripped from the atom. The field strength at which this ionization happens is strongly dependent on the state of the Rydberg atom. Pulsed electric field ionization serves, therefore, not only as a means by which a Rydberg atom may be efficiently detected, but also a means by which the state of the Rydberg atom may be analyzed.\nThe first observation of predominantly diabatic passage to field ionization of a non-hydrogenic Rydberg atom has resulted in an improved understanding of the adiabatic and diabatic ionization processes. The magnitudes of the various field ionization features have been measured and found to agree with theory, and by detailed analysis, it is now possible to label the various field ionization signal features with the appropriate (VBAR)m(,l)(VBAR) quantum numbers. A much better understanding of the laser excitation process, the Rydberg state production, and the response of the excited state to an increasing electric field has enabled measurement of some Rydberg fine-structure intervals, through observation of field ionization quantum beats.