Detector Noise Module

The Detector Noise Module calculates the Noise Equivalent Power (NEP) and the 1 // noise of the selected detection system. This module is flexible and different types of detectors will require the computation of different parameters. The detector selected for further development is the Lumped Element Kinetic inductance Detector (Doyle et al. 2008), LeKID, as it presents the most promising solution high sensitivity spectro-spatial interferometry. For the current version of the simulator, a single pixel and single mode detector is assumed for simplicity and computational reasons. 

Kinetic Inductance Detectors (KIDs) are the most promising candidate for future space and ground based spectroscopy at sub-millimetre wavelengths (Mazin 2009 Zmuidzinas 2012 Baselmans 2012). They provide a promising solution to the problem of producing large format arrays of ultra sensitive detectors for astronomy. Traditionally KIDs have been constructed from superconducting quarter-wave resonant elements capacitively coupled to a co-planar feed line. 

The principal of operation for any KID device is to measure the change in quasiparticle population within the volume of a superconducting film upon photon absorption and is shown in Fig.4.11. Any photon with an energy hf 2A, where A is 

One way of solving the problem of optical coupling THz radiation to a KID device is to use a Lumped Element KID (LeKID), which unlike its distributed counterpart shows no current variation across the device. This means the device itself can act as the absorber as well as the sensing element in a detector system. The device is based on a series LC circuit inductively coupled to a microstrip feed line. 

Regarding the optical coupling to a LeKID, simulations show (Doyle et al. 2008) that in the absence of a substrate and by tuning the thickness of the meander alone 

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The most important part of any CMB experiment is the modulation scheme that allows one to measure //K signals in the presence of 100 K instrumental foregrounds. A good modulation scheme is much more important than high sensitivity, since detector noise can always be beaten down as l/ /f by integrating longer, while a systematic error is wrong forever. 

Therefore, especially in SPR sensors with intensity modulation, the light source noise can dominate over the shot noise and detector noise and needs to be reduced by other means. 

At the Detector Noise Moduie, the Noise Equivalent Power (NEP) associated to the detectors and the 1 // noise are calculated. In parallel, with the physical properties of the system defined, the Background Power Module calculates the background power noise due to the instmment and the Cosmic Microwave Background (CMB), Cosmic Infrared Background (CIB) and Zodiacal Light. 

Once all the simulated noises are computed, they are added to the interferograms at the Add Noise Module to simulate more realistic measurements. The simulated interferograms are then sent to the Detector Module, where the interferograms are distorted according to the detector effects such as the time response. This interferograms are then sampled and readout at the Sampling and Readout Module, which also stores the data for the data reduction and processing. 

Although the 1/f noise is computed within the Detector Module, it is included in the simulated interferograms at the Add Noise Module along with the other sources of noise. 

Once a set of interferograms Ig 8, b) has been computed as the power incident on the detectors, the Add Noise Module determines the acmal signal measured by the system, by integrating the detector response and noise to the simulated interferograms. 

The topics included here are limited to the usual types of noise in the common types of infrared photon detectors. Noise in thermal detectors, such as temperature noise in bolometers, is not included. Noise associated with the avalanche process is omitted. The detailed noise theory of phototransistors, an extension of shot noise in photodiodes, is not included. Modulation noise, an example of which arises from conductivity modulation by means of carrier trapping in slow surface states, is not included. Pattern noise, due to the... 

The high performance (better than 30 pAhs standard deviation among repeated scans taken less than a second each) of the AOTF-based system of the Bran and Luebbe instrument was achieved by the proprietary dark-field dual-beam optical module, the special high-speed RF synthesizers, the low-noise high-speed detector-preamplifier module, and the efficient fiber-optic coupling [36]. Figure 37.34 shows a typical single-scan spectrum of chloroform. The time spent to collect any one point in the spectrum was approximately 100 p,s. 

It may be convenient to work with an AC signal instead of a direct current (DC) signal amplifier stability is easier to maintain, and both amplifier and detector noise are lower. To use an AC amplifier, we must convert our constant irradiance into an alternating source. This is called modulating (or chopping) the source, and several methods are available. One common chopper is a toothed wheel that rotates. The shape of the teeth and the shape of the BB aperture determine the resulting waveform. 

A digital value representing the rms output for each pixel - usually the detector noise, but it could be the rms output due to a modulated source - sometimes called the Sigmas. ... 

In temperature modulation, the sample may be mounted on a small heater attached to a heat sink and the temperature varied cyclically by passing current pulses through the heater. If the sample is properly conducting, the current can be passed through the sample directly. Generally, for this method must be kept below 10—20 Hz, and hence there are often problems with the 1//"noise of the detector. 

The basic features of an epr spectrometer are shown in Figure 2.95. The microwave source is a Klystron tube that emits radiation of frequency determined by the voltage across the tube. Magnetic fields of 0.1 — 1 T can be routinely obtained without complicated equipment and are generated by an electromagnet. The field is usually modulated at a frequency of 100kHz and the corresponding in-phase component of the absorption monitored via a phase-sensitive lock-in detector. This minimises noise and enhances the sensitivity of the technique. It is responsible for the distinctive derivative nature of epr spectra. Thus, the spectrum is obtained as a plot of dA/dB vs. 

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