Imaging Single Photons from a Kilometer Away

Scientists in Scotland have developed an imaging technique that can capture 3-D information of single photons at distances of a kilometer, adding to the remarkable progress of single-photon detectors in the past decade. Gerard Buller and colleagues at Heriot-Watt University in Edinburgh designed and tested a prototype multispectral lidar system using a time-correlated single-photon counting technique to recover millimeter-scale information about the structure and physiology of remote objects. The technique was tested on fir tree samples and was found to be practical for 3-D imaging from airborne and space-based imaging platforms (IEEE Trans. DOI: 10.1109/TGRS.2013.2285942).

The time-of-flight lidar system uses a supercontinuum laser source emitting simultaneously at 531 nm, 570 nm, 670 nm and 780 nm at a laser repetition rate of 2 MHz. Four thick-junction-silicon single-photon avalanche diode detectors construct 3-D images of targets a kilometer away using the absolute minimum of pulsed laser power—less than 200 µW total exiting the system. The system worked in bright sunny conditions to retrieve data less than 1 cm in resolution from a 3 mm beam spot.

“The solar background is by far the highest contribution to background which can swamp the return signal if the system is not engineered properly,” said Buller. “Even in Scotland, it is sunny occasionally!”

With an x-y system spatial resolution of 50 µrad and a z-resolution of 1 cm, such an array of single-photon detectors collects vast amounts of data in a time-efficient manner, but presents a bottleneck in data processing. According to Buller, more efficient imaging processing algorithms and recent work in “first-photon imaging” at MIT have shown a potentially exciting route to using less data, which reduces acquisition time and improves processing efficiency.

The researchers say the imaging technique has many applications, such as forest mapping for environmental study. The technique lends itself to imaging in scattering media, such as underwater depth imaging, collision monitoring in moving vehicles and a host of others in a wide variety of fields. Harnessing multi-spectral single-photon depth imaging from aircraft could provide an insight into the carbon cycle—but major issues remain in providing sufficient multi-spectral data from a moving platform.

Penn State Students Seek Crowdfunding To Land A Hopping Rover On The Moon

Just before winter break, students at Pennsylvania State University sat in a control room behind a two-foot-thick concrete wall. On the other side of the wall was a cryogenic rocket. As the rocket fired away, the students measured the temperature and pressure in different parts of the system, including fixtures they'd built for the rocket, all with their own handwritten computer code.

They were part of the Lunar Lion team, one of 18 teams still in the running for the Google Lunar XPrize. Lunar Lion is also the only team based at a university and comprised mostly of college students, led by Penn State staff and faculty. (Although at least one other team is a spinoff from a university.) If the Penn State students win, they could earn up to $20 million for their school. They'll also have to have landed a rover on the moon, driven the rover at least 500 meters, and sent high-definition videos and photos back to Earth. Whichever team wins the grand prize, if any, will be only the fourth "team"—after the space agencies of the former Soviet Union, the U.S., and China—to make a soft landing on the moon.

"Our goal is really education and research," Michael Paul, Lunar Lion's director and a space systems engineer at Penn State's Applied Research Laboratory, tells Popular Science. "What we're doing, we hope, becomes a model for other universities." Paul means in terms of funding. The Google Lunar XPrize is meant to stimulate the private spaceflight industry, so it requires its contestants be privately funded. The Lunar Lion team gets support from corporate and private donations and tries to work on a lean budget, Paul says. "One of the things that the students are learning is how to be frugal in their engineering."

Landing at Moon

The overall design is an all-in-one model that combines lander and rover in one vehicle. That helps save money—"otherwise we'd have to build, test and pay for essentially for two spacecraft, two spacecraft that would be bolted together," Paul says. The Lunar Lion craft will land on the surface of using small rockets, then use those same engines to "hop" the required 500 meters to win the prize. Although NASA's recent Mars rovers have been wheeled, a hopping design could help the Lunar Lion move more quickly and agilely. 

I talked briefly with Alwin Paul, an undergraduate engineering major who leads a Lunar Lion design team with another undergrad engineer, Patrick Gorski. Alwin Paul (no relation to Michael Paul) explained he's responsible for making a hovercraft that will allow him to test the craft's avionics. His group will also test the craft's individual components, including a set of feet with a honeycomb structure that will collapse as the craft lands on the surface of the moon. The honeycomb feet need to absorb 13 Gs of impact and protect the craft's delicate equipment as it lands.

The team has a little less than two years to get ready to fly. Michael Paul and his students have bought the $10 million ticket they need to hitch a ride with Phoenicia, a private launch provider based in California. They're going up in a launch window around December 19, 2015

LaTeX

%Latex is the better option for any document typing because it is unicode and free of virus also you can create PDF %using this.
%
% latex-sample.tex
%
% This LaTeX source file provides a template for a typical research paper.
%

%
% Use the standard article template.
%
\documentclass{article}

% The geometry package allows for easy page formatting.
\usepackage{geometry}
\geometry{letterpaper}

% Load up special logo commands.
\usepackage{doc}

% Package for formatting URLs.
\usepackage{url}

% Packages and definitions for graphics files.
\usepackage{graphicx}
\usepackage{epstopdf}
\DeclareGraphicsRule{.tif}{png}{.png}{`convert #1 `dirname #1`/`basename #1 .tif`.png}

%
% Set the title, author, and date.
%
\title{Sample \LaTeX-Based Research Paper}
\author{Rajeev Chaubey}
\date{}

%
% The document proper.
%
\begin{document}

% Add the title section.
\maketitle

% Add an abstract.
\abstract{
Describe your paper in 100-200 words, give or take.  The command-line \texttt{wc} utility is really useful here!  This particular sample paper is meant to demonstrate a variety of \LaTeX\ directives for producing a well-structured, consistently-formatted scholarly document.  The actual content and outline may vary according to the needs of your specific research topic.
}

% Add various lists on new pages.
\pagebreak
\tableofcontents

\pagebreak
\listoffigures

\pagebreak
\listoftables

% Start the paper on a new page.
\pagebreak

%
% Body text.
%
\section{Introduction}
\label{introduction}

You will almost certainly start with an introductory description of the topic that you investigated in your assignment.  Discuss any goals, motivation, or examples of the subject; the key is to provide the reader with any information that is necessary to understand why your topic was worth investigating.  This descriptive section should also allow the reader to understand the subsequent detail sections on the subject.

\section{Background, Preliminary, and Related Work}

Perhaps the most important functionality to learn for the paper is \LaTeX\ bibliography support.  Citations and references are handled automatically by \LaTeX\ through its companion program, \BibTeX.  All you have to do is provide a bibliography file that provides the reference information and internal keys (very much like variable names) that you use in your document.\footnote{And always remember to run \LaTeX\ \emph{at least twice} after running \BibTeX.}

\BibTeX\ supports virtually all kinds of references, including books \cite{dui,sgg,iokit,palmos}, parts of books \cite{userModeLinux}, articles \cite{nielsen:dui-review,heer-shneiderman,stackableThreads,xpkernel}, and conference proceedings \cite{ux-3d,iring,contextFileSearch,osHaskell,hibernator}, to name a few.  If not already included in your \LaTeX\ distribution, download and install the \texttt{url} package to support formatting of URLs; you can usually mention these in the \emph{note} or \emph{howpublished} fields of your \BibTeX\ file.

Like Section~\ref{introduction}, a background, preliminary, and related work section is also almost certainly needed for your paper.  In this section, describe any history, work, or projects that serve as direct contributors to the subject of your research paper.  Look at other papers in the literature to see how they organized, presented, and discussed prior work.

The Shneiderman/Plaisant text \cite{dui} provide some pointers to seminal or key works; because they made it into the textbook they aren't necessarily ``bleeding edge,'' but they likely provide the foundation for your chosen subject matter.

\section{Main Content Sections}

The outline after the introductory and background, preliminary, and related work sections is more dependent on the specific subject of your research.  Remember to cite references where appropriate, organize the material so that it flows well and is clear to the reader.

\subsection{Multiple Outline Levels}

\LaTeX\ has support for up to three outline levels (\verb!\section!, \verb!\subsection!, and \verb!\subsubsection!).  It also recognizes \verb!\paragraph! and \verb!\subparagraph! directives, though those don't show up in the table of contents.  All of these directives expect a title.

Note also the use of the \verb!\verb! directive for inserting code-like labels or symbols.  It was particularly needed here so that we can include the backslash character in the text.

\subsection{Tables and Figures}

\LaTeX\ has full support for tables and figures.  Table~\ref{table-sample} shows a sample table and Figure~\ref{figure-sample} shows a sample figure.  Note the built-in support for captions and the automated numbering functionality.  Lists of tables and figures can also be automatically generated, as seen at the beginning of this document.

\begin{table}
\centering
\begin{tabular}{|c|c|c|}\hline
Column 1 & Column 2 & Column 3 \\\hline\hline
a & b & c \\
d & e & f \\
g & h & i \\\hline
\end{tabular}

\caption{A sample table}
\label{table-sample}
\end{table}

\begin{figure}
\centering
\includegraphics[width=2in]{space.jpg} 

\caption{A sample figure}
\label{figure-sample}
\end{figure}

One very important thing to remember about how \LaTeX\ handles tables and figures by default: you don't have to worry about where they go exactly.  The general rule is that you insert them in the source after your first reference to them, and \LaTeX\ determines their final position.  It also makes decisions on how much page space to devote to them.  This all follows \LaTeX's overall theme of focusing on the content of your paper, and not its format.

Just so you can see a second table, Table~\ref{table-sample2} is provided.

\begin{table}
\centering
\begin{tabular}{|c|c|c|}\hline
Column 1 & Column 2 & Column 3 \\\hline\hline
a & b & c \\
d & e & f \\
g & h & i \\\hline
\end{tabular}

\caption{Another sample table}
\label{table-sample2}
\end{table}

\section{Another Section}

We're adding another section just so you can see how that looks.  Plus there are a few more \LaTeX\ features to illustrate.

\subsection{Bulleted and Numbered Lists}

\LaTeX\ is very good at providing clean lists.  Examples are shown below.

\begin{itemize}
\item Bulleted items come out properly indented and spaced, every time.

\begin{itemize}
\item Sub-bullets are a virtual no-brainer: just nest another \verb!itemize! block.
\item Note how the bullet character automatically changes too.
\end{itemize}

\item Just keep on adding \verb!\item!s\ldots

\item \ldots until you're done.
\end{itemize}

Numbered lists are almost identical, except that you specify \verb!enumerate! instead of \verb!itemize!.  List items are specified in exactly the same way (thus making it easy to change list types).

\begin{enumerate}
\item A list item
\item Another list item
\item A list item with multiple nested lists

\begin{itemize}
\item Nested lists can be of mixed types.
\item That's a lot of power and flexibility for the price of learning a handful of directives.

\begin{enumerate}
\item Like nested bullet lists, nested numbered lists also ``intelligently'' change their numbering schemes.
\item Meanwhile, all \emph{you} have to write is \verb!\item!.  \LaTeX\ does the rest.
\end{enumerate}
\end{itemize}

\item Back to your regularly scheduled list item

\end{enumerate}

\subsection{Subsection with Another Figure}

We may as well include a second figure also, shown in Figure~\ref{figure-sample2}.  The same image file is used, but note how it can be resized.  Again, observe how the positions of the tables and figures do not necessarily match their positions in the source file, reiterating the aforementioned \LaTeX\ functionality for deciding where these items go in the final document.  You provide an approximate location, and \LaTeX\ does the rest.

\begin{figure}
\centering
\includegraphics[width=1in]{space.jpg} 

\caption{Another sample figure}
\label{figure-sample2}
\end{figure}

\section{Conclusion}

Wrap up your paper with an ``executive summary'' of the paper itself, reiterating its subject and its major points.  If you want examples, just look at the conclusions from the literature.

% Generate the bibliography.
\bibliography{latex-sample}
\bibliographystyle{unsrt}

\end{document}

First ever DBM trained using a quantum computer

In Terminator 2, Arnold reveals that his CPU is a neural net processor, a learning computer. Of course it is! What else would it be? Interestingly, there are real neural net processors in the world. D-Wave makes the only superconducting version, but there are other types out there also. Today we’ll use one of our superconducting neural nets to re-run the three experiments we did last time.

I believe this is the first time quantum hardware has been used to train a DBM, although there have been some theoretical investigations.

Embedding into hardware

Recall that the network we were training in the previous post had one visible layer with up to four units, and two hidden layers each with four units. For what follows we’re going to associate each of these units with a specific qubit in a Vesuvius processor. The way we’re going to do this is to use a total of 16 qubits in two unit cells to represent the 12 units in the DBM.

All D-Wave processors can be thought of as hardware neural nets, where the qubits are the neurons and the physical couplers between pairs of qubits are edges between qubits.Specifically you should think of them as a type of Deep Boltzmann Machine (DBM), where specifying the biases and weights in a DBM is exactly like specifying the biases and coupling strengths in a D-Wave processor. As in a DBM, what you get out are samples from a probability distribution, which are the (binary) states of the DBM’s units (both visible and hidden).

In the Vesuvius design, there is an 8×8 tile of eight-qubit unit cells, for a total of 512 ‘neurons’. Each neuron is connected to at most 6 other neurons in Vesuvius. To do the experiments we want to do, we only need two of the 64 unit cells. For the experts out there, we could use the rest to do some interesting tricks to use more of the chip, such as gauge transformations and simple classical parallelism, but for now we’ll just stick to the most basic implementation.

Tech fest

Successful launch of Sentinel-1A – the satellite carries optical systems of the Berliner Glas Group

On 03 April 2014, shortly after 11:00 p.m., Sentinel-1A, a polar-orbiting satellite, was launched successfully on a Soyuz rocket from Europe’s Spaceport Kourou in French Guiana.

Sentinel-1A is the first satellite of the ESA Sentinel fleet, that has been developed specifically to provide large amounts of data and pictures for the Earth observation program Copernicus. Sentinel-1A will orbit the Earth at an altitude of a few hundred kilometers (in a low Earth orbit) and will provide all-weather, day and night radar imagery for land and ocean services.

A laser communications terminal (LCT) of Tesat-Spacecom also is on board Sentinel-1A. This laser communications terminal includes several optical components and systems of the Berliner Glas Group. These high-precision opto-mechanical systems designed and produced by the Berliner Glas Group at its locations in Berlin, Germany and Heerbrugg, Switzerland guide and process the laser light in the transmission as well as receiver channels of the laser communications terminal. The highest requirements had to be realized to ensure an error-free operation during the entire lifetime of the satellite in space.

The laser communications terminal on board Sentinel-1A is another component of the European Data Relay System (EDRS) and enables high-speed data transfers between the low Earth orbit and the geostationary Earth orbit. The first high-volume data connection between the laser communications terminal on Sentinel-1A and a satellite in geostationary Earth orbit is expected to be realized later on this year.

Fourier Transform

The Fourier transform, named after Joseph Fourier, is a mathematical transformation employed to transform signals between time (or spatial) domain andfrequency domain, which has many applications in physics and engineering. It is reversible, being able to transform from either domain to the other. The term itself refers to both the transform operation and to the function it produces.

This is the basic mathematical tool used for the calculation of difficult mathematical problems, specially, when the problem is related to any domain. like time domain, frequency domain, space domain and others.

Fourier transform converts every domain to s domain which has real and negative part. The poles and zeros are on either real part or on imaginary part. If they are on real axis and at negative side then the system is stable, If the are on positive side then system is unstable. If they are on imaginary axis then system is marginal stable.

Fourier transform gives the relation between time domain to frequency domain, so we can easily convert a signal in other domains.  In frequency domain it is very easier to solve and complex problem. but in time domain it very easier to design the system. So for system designing and its performance characterization we need Fourier Transform.

Fourier transform is the natural mechanism used by the nature to solve the optical problem as the lens give the Fourier transform of any signal at its focus, when signal is originated from its other focus. It can be so simple in the solving a differentiation or integral problem. Since it is in the form of exponential and differentiation and integration of the exponential is exponential.

The Fourier Transform is extensively used in the field of Signal Processing. In fact, the Fourier Transform is probably the most important tool for analyzing signals in that entire field. So what exactly is signal processing? I'll try to give a one paragraph high level overview. A signal is any waveform (function of time). This could be anything in the real world - an electromagnetic wave, the voltage across a resistor versus time, the air pressure variance due to your speech (i.e. a sound wave), or the value of Apple Stock versus time. Signal Processing then, is the act of processing a signal to obtain more useful information, or to make the signal more useful. How can a signal be made better? Suppose that you are listening to a recording, and there is a low-pitched hum in the background. By applying a low-frequency filter, we can eliminate the hum. Or suppose you have a digital photograph, and it is very noisy (that is, there are random specs of light everywhere). We can use signal processing and fourier transforms to filter out this undesirable "noise".

Fiber Bragg Grating

"FBG is a simple device used for the separation of wavelength from a group of wavelengths."  Rayc


A fiber Bragg grating (FBG) is a type of distributed Bragg reflector constructed in a short segment of optical fiber that reflects particular wavelengths of light and transmits all others. This is achieved by creating a periodic variation in the refractive index of the fiber core, which generates a wavelength specific dielectric mirror. A fiber Bragg grating can therefore be used as an inline optical filter to block certain wavelengths, or as a wavelength-specific reflector.

The first in-fiber Bragg grating was demonstrated by Ken Hill in 1978. Initially, the gratings were fabricated using a visible laser propagating along the fiber core. In 1989, Gerald Meltz and colleagues demonstrated the much more flexible transverse holographic inscription technique where the laser illumination came from the side of the fiber. This technique uses the interference pattern of ultraviolet laser light to create the periodic structure of the fiber Bragg grating.

Fiber Bragg gratings are created by "inscribing" or "writing" systematic (periodic or aperiodic) variation of refractive index into the core of a special type of optical fiber using an intense ultraviolet(UV) source such as a UV laser. Two main processes are used: interference and masking. The method that is preferable depends on the type of grating to be manufactured. Normally agermanium-doped silica fiber is used in the manufacture of fiber Bragg gratings. The germanium-doped fiber is photosensitive, which means that the refractive index of the core changes with exposure to UV light. The amount of the change depends on the intensity and duration of the exposure as well as the photosensitivity of the fibre. To write a high reflectivity fiber Bragg grating directly in the fiber the level of doping with germanium needs to be high. However, standard fibers can be used if the photosensitivity is enhanced by pre-soaking the fiber in hydrogen. More recently, fiber Bragg gratings have also been written in polymer fibers, this is described in the PHOSFOS entry

Fiber bragg grating can easily designed by using a simple fiber in presence of the interference of two ultravoilet light beam. Which give constructive and destructive interferences. At constructive interference refractive index decrease and at destructive interference refractive index remains same so we get two different refractive indices. Which periodically makes FBG.

FBG  are of two types:

1. Simple FBG 

2. Chirped FBG

 Simple FBG  in this refractive index of the dense medium is fixed. In this reflected light is the function of length of a period of refractive index.

 Chirped FBG in this refractive index of the dense medium is getting denser.In this refracted light is combination of different wavelengths are refracted at different time intervals.

Fiber Bragg Gratings are made by laterally exposing the core of a single-mode fiber to a periodic pattern of intense ultraviolet light. The exposure produces a permanent increase in the refractive index of the fiber's core, creating a fixed index modulation according to the exposure pattern. This fixed index modulation is called a grating.

At each periodic refraction change a small amount of light is reflected. All the reflected light signals combine coherently to one large reflection at a particular wavelength when the grating period is approximately half the input light's wavelength. This is referred to as the Bragg condition, and the wavelength at which this reflection occurs is called the Bragg wavelength. Light signals at wavelengths other than the Bragg wavelength, which are not phase matched, are essentially transparent.

Therefore, light propagates through the grating with negligible attenuation or signal variation. Only those wavelengths that satisfy the Bragg condition are affected and strongly back-reflected. The ability to accurately preset and maintain the grating wavelength is a fundamental feature and advantage of fiber Bragg gratings.

The central wavelength of the reflected component satisfies the Bragg relation: λrefl=2nΛ, with n the index of refraction and Λ the period of the index of refraction variation of the FBG. Due to the temperature and strain dependence of the parameters n and Λ, the wavelength of the reflected component will also change as function of temperature and/or strain, see Figure 2. This dependency is well known what allows determining the temperature or strain from the reflected FBG wavelength.

There have been many advances in the methods used to perform strain measurements. The three most prevalent technologies today are electrical foil gages, electrical vibrating wire, and fiber Bragg grating (FBG) optical sensors. 

For most standard strain sensing applications, electrical sensing has been and will continue to be the best and most effective solution. However, optical sensors can offer an important alternative in traditionally challenging applications. Harsh environments, distributed systems, or long-term deployments are a few examples where the characteristics of an optical sensing system can make it a more effective solution compared to conventional electrical sensors. 

Applications often require measurement solutions that encompass the benefits and attributes of multiple sensing technologies. It is therefore important to consider a hybrid approach. This paper provides a brief overview of each technology and weighs their benefits and drawbacks.

Electrical Sensing: Metal Foil Gages

Foil strain gages use the relationship between electrical resistance and conductor length to measure changes in strain. As the foil is stretched, its length is increased, which translates into a minute increase in resistance. To accurately measure these small changes in resistance, additional signal conditioning is necessary, often in the form of a Wheatstone bridge resistance network. A constant voltage is applied across the resistance network, and the varying proportional drop in voltage across the foil can be translated to strain.

Gradient Force

"Gradient" refers to how rapidly a quantity (such as pressure or temperature) changes in a given distance. It can be thought of as measure of "steepness", like the topography on a contour plot.

The pressure gradient force is the force which results when there is a difference in pressure across a surface. In general, a pressure is a force per unit area, across a surface. A difference in pressure across a surface then implies a difference in force, which can result in an acceleration according to Newton's second law, if there is no additional force to balance it. The resulting force is always directed from the region of higher-pressure to the region of lower-pressure. When a fluid is in an equilibrium state (i.e. there are no net forces, and no acceleration), the system is referred to as being in hydrostatic equilibrium. In the case of atmospheres, the pressure gradient force is balanced by the gravitational force, maintaining hydrostatic equilibrium. In the Earth's atmosphere, for example, air pressure decreases at increasing altitudes above the Earth's surface, thus providing a pressure gradient force which counteracts the force of gravity on the atmosphere

In optical tweezer Gradient force is used to compensate Scattering force.

In cases where the diameter of a trapped particle is significantly greater than the wavelength of light, the trapping phenomenon can be explained using ray optics. As shown in the figure, individual rays of light emitted from the laser will be refracted as it enters and exits the dielectric bead. As a result, the ray will exit in a direction different from which it originated. Since light has a momentum associated with it, this change in direction indicates that its momentum has changed. Due to Newton's third law, there should be an equal and opposite momentum change on the particle.

Most optical traps operate with a Gaussian beam (TEM₀₀ mode) profile intensity. In this case, if the particle is displaced from the center of the beam, as in the right part of the figure, the particle has a net force returning it to the center of the trap because more intense beams impart a larger momentum change towards the center of the trap than less intense beams, which impart a smaller momentum change away from the trap center. The net momentum change, or force, returns the particle to the trap center.

If the particle is located at the center of the beam, then individual rays of light are refracting through the particle symmetrically, resulting in no net lateral force. The net force in this case is along the axial direction of the trap, which cancels out the scattering force of the laser light. The cancellation of this axial gradient force with the scattering force is what causes the bead to be stably trapped slightly downstream of the beam waist.

This is the output when beam is linear.

If the particle is located at the center of the beam, then individual rays of light are refracting through the particle symmetrically, resulting in no net lateral force. The net force in this case is along the axial direction of the trap, which cancels out the scattering force of the laser light. The cancellation of this axial gradient force with the scattering force is what causes the bead to be stably trapped slightly downstream of the beam waist.

This is the output, when beam is focused.

The standard tweezers works with the trapping laser propagated in the direction of gravity and the inverted tweezers works against gravity.

Wind is simply air in motion relative to the earth's surface. We normally think of the wind as the horizontal motion of the air, although air actually moves in three dimensions. The vertical component of the wind is generally quite small, except in thunderstorm updrafts. The vertical motion of air, however, is very important in determining our weather. Air that is rising cools, which may cause it to reach saturation and form clouds and precipitation. Conversely, air that is sinking warms, which causes clouds to evaporate and produce clear weather.

Surface maps usually have H's and L's at various locations. The H's and L's represent high and low pressure systems. On weather maps highs and lows are surrounded by lines called isobars. Isobars are lines of constant pressure; they connect every location that has the same value of pressure. When isobars are packed close together, the pressure is changing rapidly over a small distance. The closer the isobars are packed together, the stronger thepressure gradient (the rate of pressure change over a given distance.) Also, notice that (in the Northern Hemisphere) the wind blows clockwise around a high pressure system and also slightly outward from its center. Around a low pressure system, the wind blows counterclockwise and slightly in towards its center.

Diffraction Limit

An ideal optical system would image an object point perfectly as a point. However, due to the wave nature of radiation, diffraction occurs, caused by the limiting edges of the system’s aperture stop. The result is that the image of a point is a blur, no matter how well the lens is corrected. This is the diffraction blur or Airy disk, named in honor of Lord George Biddel Airy, a British mathematician (1801–1892). Its cross section and its appearance are shown in the figure below.

Airy disk, energy distribution and appearance.

If an image is made through a small aperture, there is a point at which the resolution of the image is limited by the aperture diffraction. As a matter of general practice in photographic optics, the use of a smaller aperture (larger f-number) will give greater depth of field and a generally sharper image. But if the aperture is made too small , the effects of the diffraction will be large enough to begin to reduce that sharpness, and you have reached the point of diffraction-limited imaging.

If you are imaging two points of light, then the smallest separation at which you could discern that there are two could reasonably be used as the limit of resolution of the imaging process. Presuming that diffraction is the determining factor, then the generally accepted criterion for the minimum resolvable detail is the Rayleigh criterion.

This shows the intensity curves for the radial distribution of the diffracted light for different separations. Your eye sees the characteristic bulls eye distribution of light as illustrated below.

For modern digital photography where the images are projected onto a CCD, the information is collected on pixels of the digital detector. At left is an attempt to show the effect of diffraction on such imaging in cases where the diffraction is the phenomenon that limits the resolution. If the image is in focus and free of visible affects of lens aberrations, then it may be that it will fit on one pixel. But if the aperture is small enough, then diffraction can spread the image onto neighboring pixels and constitute the limit on the resolution of the image.

Diffraction of any image reduces its sharpness and losses the frequency component inside it. Since there is lot much noise comes in even scent modes.