Prof. Thejesh Bandi
Physics and Astronomy, The University of Alabama, Tuscaloosa, Alabama, USA
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Academic Career Length
20Years (2007-Present)
(Calculated once Scilit publication data is synced: current year − year of first publication + 1)
Representative Publications
View All Publications6 November 2014 in IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control
Journal Article
Thejesh BandiCAChristoph Affolderbach
Christoph AffolderbachCSCamillo Stefanucci
Camillo Stefanucci
FMFrancesco Merli
Francesco Merli
ASAnja K. Skrivervik
Anja K. Skrivervik
GMGaetano Mileti
Gaetano Mileti
We present our studies on a compact high-performance continuous wave (CW) double-resonance (DR) rubidium frequency standard in view of future portable applications. Our clock exhibits a short-term stability of 1.4 × 10 -13 τ -1/2 , consistent with the short-term noise budget for an optimized DR signal. The metrological studies on the medium- to longterm stability of our Rb standard with measured stabilities are presented. The dependence of microwave power shift on light intensity, and the possibility to suppress the microwave power shift is demonstrated. The instabilities arising from the vapor cell geometric effect are evaluated, and are found to act on two different time scales (fast and slow stem effects). The resulting medium- to long-term stability limit is around 5.5 × 10 -14 . Further required improvements, particularly focusing on medium- to long-term clock performance, are discussed.
1 October 2012 in Review of Scientific Instruments
Journal Article
CSCamillo Stefanucci
Camillo Stefanucci
Thejesh BandiFMFrancesco Merli
Francesco Merli
MPMatthieu Pellaton
Matthieu Pellaton
CAChristoph Affolderbach
Christoph AffolderbachASAnja K. Skrivervik
Anja K. Skrivervik
+1
The design, realization, and characterization of a compact magnetron-type microwave cavity operating with a TE011-like mode are presented. The resonator works at the rubidium hyperfine ground-state frequency (i.e., 6.835 GHz) by accommodating a glass cell of 25 mm diameter containing rubidium vapor. Its design analysis demonstrates the limitation of the loop-gap resonator lumped model when targeting such a large cell, thus numerical optimization was done to obtain the required performances. Microwave characterization of the realized prototype confirmed the expected working behavior. Double-resonance and Zeeman spectroscopy performed with this cavity indicated an excellent microwave magnetic field homogeneity: the performance validation of the cavity was done by achieving an excellent short-term clock stability as low as 2.4 × 10−13 τ−1/2. The achieved experimental results and the compact design make this resonator suitable for applications in portable atomic high-performance frequency standards for both terrestrial and space applications.
30 June 2015 in IEEE Transactions on Instrumentation and Measurement
Journal Article
CAChristoph Affolderbach
Christoph AffolderbachGDGuan-Xiang Du
Guan-Xiang Du
Thejesh BandiAHAndrew Horsley
Andrew Horsley
PTPhilipp Treutlein
Philipp TreutleinGMGaetano Mileti
Gaetano Mileti
We report on the experimental measurement of the dc and microwave magnetic field distributions inside a recently developed compact magnetron-type microwave cavity mounted inside the physics package of a high-performance vapor-cell atomic frequency standard. Images of the microwave field distribution with sub-100-μm lateral spatial resolution are obtained by pulsed optical-microwave Rabi measurements, using the Rb atoms inside the cell as field probes and detecting with a CCD camera. Asymmetries observed in the microwave field images can be attributed to the precise practical realization of the cavity and the Rb vapor cell. Similar spatially resolved images of the dc magnetic field distribution are obtained by Ramsey-type measurements. The T 2 relaxation time in the Rb vapor cell is found to be position dependent and correlates with the gradient of the dc magnetic field. The presented method is highly useful for experimental in situ characterization of dc magnetic fields and resonant microwave structures, for atomic clocks or other atom-based sensors and instrumentation.
9 June 2011 in Electronics Letters
Journal Article
Thejesh BandiCAC. Affolderbach
C. AffolderbachCCC.E. Calosso
C.E. Calosso
GMG. Mileti
G. Mileti
Presented is a double-resonance continuous-wave laser-pumped rubidium (Rb) atomic clock with a short-term stability of 4×10−13 τ−1/2 for integration times 1 s≤τ≤1000 s, and a medium- to long-term stability reaching the 1×10−14 level at 104 s. The clock uses an Rb vapour cell with increased diameter of 25 mm, accommodated inside a newly developed compact magnetron-type microwave cavity. This results in a bigger signal with reduced linewidth, and thus improved short-term stability from a clock with 1 dm3 physics package volume only. The medium- to long-term clock stability is achieved by minimising the effects of light-shift and temperature coefficient on the atoms. Potential applications of the clock are discussed.
5 January 2023 in Biology, Engineering, Medicine and Science Reports
Journal Article
Thejesh BandiTime is ubiquitous, and integral to our everyday lives. Precise measurement of time intervals is basic to various activities humans are dependent up on, such as accurate positioning using satellite navigation, telecommunication, aviation, definition of International Time, secondary applications using positioning, military applications etc. Atomic clocks formulate the heart of precise time measurement and hence enable the positioning and navigation and niche time and frequency dependent technologies that we rely upon directly or otherwise. This paper gives a comprehensive overview of history of time measurement and evolution of clocks towards atomic clocks. It broadly covers various types of atomic clocks ranging from laboratory clocks to miniature commercial clocks along with the key applications with a focus on microwave atomic clocks (or frequency standards). Further, the satellite navigation systems operational around the globe by various countries and the types of clocks used for such navigation systems are briefly covered with a focus on the rubidium atomic frequency standard and other space clocks.
15 June 2012 in Journal of Applied Physics
Journal Article
Thejesh BandiCAChristoph Affolderbach
Christoph AffolderbachGMGaetano Mileti
Gaetano Mileti
We have realized and studied a rubidium atomic frequency standard based on a paraffin-coated cell, exhibiting a short-term frequency stability <3 × 10−12 τ−1/2 between τ = 1 and 100 s. Characterization of the wall-coating is performed by measuring the T1 and T2 relaxation times. Perturbations of the medium- to long-term clock stability, due to variations in the laser-intensity, laser frequency, the microwave power shift, and the shifts due to temperature variations are measured and analyzed. A method for reducing the intensity light-shift by detuning the laser frequency and the resulting improvement in clock stability is demonstrated. This work is of relevance for further improvements on Rb cell standards using anti-relaxation wall-coating technology.
About Me
Dr. Thejesh N. Bandi is an associate professor at the University of Alabama (UA) and the principal investigator of the Quantime Lab at UA. With two decades of experiences in high-end oscillators, atomic clocks, satellite navigation and timescale generation, Dr.Bandi has designed, developed, and qualified precision atomic clocks for ground and space navigation missions – the recent being successful first ever Indian Rubidium clock onboard NavIC constellation which he led the design and development at the Indian Space Research Organisation (ISRO). Dr. Bandi has a PhD from the University of Neuchâtel, Switzerland, and was a postdoctoral fellow at NASA’s Jet Propulsion Lab/Caltech, and Head of the clocks division at the ISRO. Dr. Bandi is a senior IEEE member and an active member of the Institute of Navigation. He is also life member of the American Physical Society and Optica. His research interests span from basic atomic and ion spectroscopy to its novel implementation methods with the atomic and optical clocks; quantum metrological studies; time scales and synchronization schemes; and Machine Learning methods for time and frequency metrology and safe and alternate GNSS. Dr. Bandi is also active in training the next-generation skilled manpower for the sustenance and growth of the PNT field.