Mehdi Alem

Mehdi Alem is an Application Scientist at Zurich Instruments. He received his PhD in photonics from EPFL in Lausanne. His background is in nonlinear optics, electrical engineering, and signal processing. Before moving to Switzerland, he studied and worked at Sharif University of Technology in Iran. At Zurich Instruments, Mehdi likes to address experimental and theoretical challenges posed by colleagues and customers. His interests include mathematics, physics, music, the humanities, and programming.

How to Control Spectral Leakage with Window Functions in LabOne

25.11.2021

Symmetric and asymmetric window functions

Spectral characterization of signals and systems is required in a broad range of applications in physics and engineering. Analyzing a signal in the frequency domain reveals valuable information about the signal behavior which is not necessarily obtainable from its time-domain analysis...

Noise Spectral Density Measured with Lock-in Amplifiers

15.08.2021

Proper noise characterization is essential in many applications, especially when dealing with tiny signals buried in noise like in nanotechnology, photonics and quantum physics. Noise characteristics of a system are often represented by the noise spectral density in amplitude or power mode, the latter being called power spectral density (PSD), within the frequency range of interest...

Retrieving the Carrier Frequency of Phase-Modulated or Carrier-Suppressed Signals with Costas Loops

08.11.2020

Phase-locked loops (PLLs) are widely used to recover the frequency of a carrier signal in many detection systems such as lock-in amplifiers and data receivers. To properly lock to the carrier phase and extract its frequency, a clean reference separate from the signal or a pilot tone within the signal must be provided for the PLL...

How to Generate QAM Signaling with the HDAWG

25.11.2019

Digital modulation is extensively used in telecommunications, radar systems and quantum technologies. Corresponding to every analog modulation technique, i.e., amplitude modulation (AM), phase modulation (PM) and frequency modulation (FM), there is a digital version of signal modulation...

Synchronizing Multiple MFLI Lock-in Amplifiers

16.09.2019

Multi-channel signal generation and detection are indispensable in many applications such as multi-qubit quantum computing and multi-sensor systems. Synchronization of signal channels comes to the equation when the temporal sequence of events is of interest, especially for fast physical phenomena with short lifetimes...

Frequency-Domain Response of Lock-in Filters

19.03.2019

Introduction The response of a lock-in amplifier is characterized by the parameters of its low-pass filter (LPF), i.e., time constant and filter order. The temporal response of the LPF demonstrates the latency of measurement while its spectral response shows the noise characteristics of measured signals. This blog post explains how...

How to Demodulate Multi-frequency Signals such as AM, FM and PM

20.03.2018

Introduction When analyzing signals with multiple frequency components, it is important to measure the amplitude and phase of each frequency component accurately so that a change in the characteristics of one component does not affect the measurement of another frequency component. There are two different approaches to multi-frequency signal demodulation...

Generation of Single-Sideband Modulation by Arbitrary Waveform Generators

15.12.2017

Introduction I/Q modulations are extensively used in a variety of applications including telecommunications, quantum computing (QC), nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR) spectroscopy and band-excitation atomic force microscopy (AFM). In this post, we demonstrate how to generate such signals using arbitrary waveform generators from Zurich Instruments with an...

Kramers–Kronig Test Applied to Impedance Measurements of Electrical Circuits

25.09.2017

Introduction In this post, the Kramers-Kronig relations are used to verify the results of an impedance measurement experiment performed with the Zurich Instruments MFIA Impedance Analyzer or the MFLI Lock-in Amplifier equipped with the MF-IA option. The Kramers-Kronig relations state that the real part of the impedance can be obtained...

Noise Analysis of Signal Components

29.03.2017

In this blog post, we investigate the relation between the noise of signal amplitude and phase on one hand, and the noise of in-phase and quadrature components of the signal on the other hand. We try to respond to the wrong intuition stating that the standard deviation of signal amplitude is higher than the standard deviation of each signal components...

Time-Domain Response of Lock-in Filters

09.02.2017

The heart of a lock-in amplifier is a phase-sensitive detector that includes a signal mixer and a low-pass filter. In this blog post, we focus on the time response of the low-pass filters implemented in the Zurich Instruments lock-in amplifiers including the MFLI, the HF2LI and the UHFLI...

The Nyquist Diagram for Electrical Circuits

11.01.2017

The Nyquist diagram of a transfer function is a parametric plot of its imaginary part versus real part as the frequency sweeps in a certain range. When dealing with electric circuits, the transfer function is the immittance of the circuit, i.e., it can be either the impedance or the admittance of the circuit...