Ramiz Hamid

Sub-50 fs Yb-doped laser with anomalous-dispersion photonic crystal fiber

We report on the generation of 42 fs pulses at 1 μm in a completely fiber-integrated format, which are, to the best of our knowledge, the shortest from all-fiber-integrated Yb-doped fiber lasers to date. The ring fiber cavity incorporates anomalous-dispersion, solid-core photonic crystal fiber with low birefringence, which acts as a broadband, in-fiber Lyot filter to facilitate mode locking. The oscillator operates in the stretched-pulse regime under slight normal net cavity dispersion. The cavity generates 4.7 ps long pulses with a spectral bandwidth of 58.2 nm, which are dechirped to 42 fs via a grating pair compressor outside of the cavity. Relative intensity noise (RIN) of the laser is characterized, with the integrated RIN found to be 0.026% in the 3 Hz-250 kHz frequency range.

Picometre displacement measurements using a differential Fabry–Perot optical interferometer and an x-ray interferometer

X-ray interferometry is emerging as an important tool for dimensional nanometrology both for sub-nanometre measurement and displacement. It has been used to verify the performance of the next generation of displacement measuring optical interferometers within the European Metrology Research Programme project NANOTRACE. Within this project a more detailed set of comparison measurements between the x-ray interferometer and a dual channel Fabry–Perot optical interferometer (DFPI) have been made to demonstrate the capabilities of both instruments for picometre displacement metrology. The results show good agreement between the two instruments, although some minor differences of less than 5 pm have been observed.

Measurement of electromagnetic radiation from GSM base stations

Electromagnetic radiations from GSM (global service for mobile communication) base stations were measured in the far-field region by using directional antennas (biconical-log/hybrid, horn antenna) and isotropic electric field probes and detected signals were analyzed by using low-resolution bandwidth (30 Hz) spectrum analyzer and field probe meter respectively. Electric fields of the electromagnetic radiations were measured in x, y and z orthogonal directions with vertical and horizontal polarizations. Amplitude fluctuation of electromagnetic radiation of GSM base station were detected at long time interval (more than 8 hours) and analyzed using standard deviation and Allan variance statistics. The results and uncertainties of the electric field measurements by biconical-log/hybrid antenna, horn antenna and electric field probe were compared. The measured electric field values of GSM base stations were compared to the value of reference levels for general public exposure to time-varying electric fields limits of ICNRP guidelines.

Loop-Antenna Calibration

Loop-antenna calibration is discussed in this tutorial. Loop antennas are especially used in low-frequency radiated-emission (RE) and radiated-susceptibility (RS) measurements and tests. These are important in commercial systems, but critical in military systems. The standards used for this purpose are reviewed, and comparisons among them are made. Results are presented with commercial as well as home-made loop antennas.

Characterization of a Far-Field Microwave Magnetic Field Strength Sensor Based on Double Radiooptical Resonance

We experimentally investigated the resonance interaction of laser and microwave fields with 133Cs atomic gas in far-field and free-space conditions. The observed double radiooptical resonance (DROR) on the D2 line of Cs atoms was used as a novel-type field sensor, based on the laser spectroscopy technique, for the detection and investigation of the time-varying magnetic field. The effects of the Cs cell length, both laser and microwave powers, and their polarizations to the changing amplitude of the DROR signal were investigated. Almost linear dependencies of the DROR signal amplitude with both laser and microwave powers have been observed. The splitting of DROR signal under a constant magnetic field was detected. The time response of the sensor system was investigated under pulsed microwave. The amplitude fluctuation of the microwave magnetic field was measured using the DROR signal and the isotropic probe simultaneously. The stability of amplitude fluctuations of the microwave field with time was analyzed by using Allan variance statistics.

The temperature stabilization and temperature measurement of a Kösters interferometer

In this work, the mechanical design, optical setup and temperature measurement system of a Kosters interferometer are described for the length measurements of long gauge blocks. The temperature variation of 9 mK at 15 °C and 2 mK at 20 °C was measured inside the interferometric chamber using the six air and four surface thermistors. The temperature stability is analysed by using standard deviation and Allan variance statistics.

Sensing of RF Magnetic Fields Using Zeeman Splitting of Double Radiooptical Resonance and a New Approach to Helmholtz Coil Calibrations

We experimentally investigated the resonance interaction of laser, microwave, and radio frequency (RF) fields with Cesium (133Cs) atomic gas. The observed Zeeman components produced by means of an external static magnetic field on the double radiooptical resonance (DROR) were used as a frequency-adjustable RF field detection sensor based on the laser spectroscopy technique. The change in the RF interaction frequency of Zeeman components with the increasing level of the static magnetic field was investigated and linear dependence of the RF interaction frequency of the Zeeman components on the external static magnetic field was observed. In addition, the change in the amplitude of the Zeeman components with the level of RF fields was investigated and an approximately linear relation in certain regions was detected. We also studied the relation of the Zeeman component amplitudes with laser and microwave powers. Finally, a new approach to Helmholtz coil calibrations by using this atomic sensor is discussed.

Application of the differential Fabry–Perot interferometer in angle metrology

A differential Fabry–Perot interferometer (DFPI) was applied for the detection of ultra-small angles in the level of nanoradian (nrad) precision. During application, down to 1 nrad angular steps were generated using the available high precision small angle generator (HPSAG) and these steps were detected using the frequency stabilised lasers as an alternative and outperforming method to conventional angle interferometers. The use of the DFPI provided the displacement measurements (further angular displacements through optical configuration) with picometre sensitivity free from linearity errors. A coefficient of 1.436 964 × 10−9 arcsec Hz−1 (about 7 × 10−6 nrad Hz−1) for the DFPI was calculated using the generated–measured traceable angular values of the HPSAG and various angular steps were measured by the DFPI using this coefficient. The tests were carried out up to the range of 0.5 arcsec (2500 nrad) in angular steps down to 1 nrad. The work is in progress under the SIB58 Angles project and aims to reduce the noise level of the HPSAG with further statistical process and later to extend the measurement range of the DFPI readings with the same optical configuration, rather than using different beam spacing configuration in the DFPI.

High contrast resonances of the coherent population trapping on sublevels of the ground atomic term

We have detected and analyzed narrow, high contrast coherent population trapping resonances, which appear in transmission of the probe monochromatic light beam under action of the counterpropagating two-frequency laser radiation, on example of the nonclosed three level Λ-system formed by spectral components of the Doppler broadened D2 line of cesium atoms (in the cell with the rarefied Cs vapor). These nontrivial resonances are determined directly by the trapped atomic population on the definite lower level of the Λ-system and may be used in atomic frequency standards, sensitive magnetometers and in ultrahigh resolution laser spectroscopy of atoms and molecules.

Toward Absolute Measurements of Far-Field Microwave Magnetic Field by Atomic Sensor Based on Double Radiooptical Resonance

By using Cs atomic sensor, the differences between the measurement results of double radiooptical resonance (DROR) and the ratio of Doppler amplitude to DROR signal (Doppler/DROR) for the far-field microwave magnetic field were illustrated experimentally. The effects of laser power and atomic sensor temperature to the DROR and Doppler/DROR ratio were investigated. At constant laser power, Cs atomic cell temperature and microwave magnetic field strength, the maximum deviations for DROR and Doppler/DROR ratio were calculated over time. The fluctuation of the Doppler/DROR ratio measurement results was calculated approximately as 0.5 dB in 24-h measurement time interval. On the other hand, the fluctuation of the measured DROR values was calculated as 0.9 dB in the same time interval. As a consequence, Doppler/DROR ratio measurements yield better and repeatable results by comparison with DROR measurements.