Be More Curious....RAMAN EFFECT !

Theory of Raman Scattering

When considering Raman scattering, we can think about the physics in one of two ways: the classical wave interpretation or the quantum particle interpretation. In the classical wave interpretation, light is considered as electromagnetic radiation, which contains an oscillating electric field that interacts with a molecule through its polarizability. Polarizability is determined by the electron cloud’s ability to interact with an electric field. For example, soft molecules such as benzene tend to be strong Raman scatterers while harder molecules like water tend to be fairly weak Raman scatterers.

Figure R-2 Comparison of Raman Scattering Interpretations

When considering the quantum particle interpretation, light is thought of as a photon which strikes the molecule and then inelasticaly scatters. In this interpretation the number of scattered photons is proportional to the size of the bond. For example, molecules with large Pi bonds such as benzene tend to scatter lots of photons, while water with small single bonds tends to be a very weak Raman scatterer. Figure R-2 shows a visual comparison of the two methods.

When deriving the Raman effect, it is generally easiest to start with the classical interpretation by considering a simple diatomic molecule as a mass on a spring (as shown in figure R-3) where m represents the atomic mass, x represents the displacement, and K represents the bond strength.

Figure R-3 Diatomic Molecule as a Mass on a Spring

When using this approximation, the displacement of the molecule can be expressed by using Hooke’s law as,

Equation R-1

By replacing the reduced mass (m1m2/[m1+m2]) with μ and the total displacement (x1+x2) with q, the equation can be simplified to,

Equation R-2

By solving this equation for q we get,

Equation R-3

where νm is the molecular vibration and is defined as,

Equation R-4

From equations R-3 and R-4, it is apparent that the molecule vibrates in a cosine pattern with a frequency proportional to the bond strength and inversely proportional to the reduced mass. From this we can see that each molecule will have its own unique vibrational signatures which are determined not only by the atoms in the molecule, but also the characteristics of the individual bonds. Through the Raman effect, these vibrational frequencies can be measured due to the fact that the polorizability of a molecule, α, is a function of displacement, q. When incident light interacts with a molecule, it induces a dipole moment, P, equal to that of the product of the polorizability of the molecule and the electric field of the incident light source. This can be expressed as,

Equation R-5

where Eo is the intensity and νo is the frequency of the electric field. Using the small amplitude approximation, the polorizability can be described as a linear function of displacement,

Equation R-6

which when combined with equations R-3 and R-5 results in,

Equation R-7

In Equation R-7 we see that there are two resultant effects from the interaction of the molecule and the incident light. The first effect is called Rayleigh scattering, which is the dominate effect and results in no change in the frequency of the incident light. The second effect is the Raman scattered component and when expanded to,

Equation R-8

can be shown to shift the frequency of the incident light by plus or minus the frequency of the molecular vibration. The increase in frequency is known as an Anti-Stokes shift and the decrease in frequency is known as a Stokes shift. By measuring the change in frequency from the incident light (typically only the Stokes shift is used for this measurement) the Raman effect now gives spectroscopists a means of directly measuring the vibrational frequency of a molecular bond.

Now that we have derived the Raman effect using the classical wave interpretation, we can use the quantum particle interpretation to better visualize the process and determine additional information. As discussed earlier in the quantum interpretation, the Raman effect is described as inelastic scattering of a photon off of a molecular bond. From the Jablonski diagram shown in figure R-4, we can see that this results from the incident photon exciting the molecule into a virtual energy state.

Figure R-4 Jablonski Diagram Representing
Quantum Energy Transitions for Rayleigh and Raman Scattering

When this occurs, there are three different potential outcomes. First, the molecule can relax back down to the ground state and emit a photon of equal energy to that of the incident photon; this is an elastic process and is again referred to as Rayleigh scattering. Second, the molecule can relax to a real phonon state and emit a photon with less energy than the incident photon; this is called Stokes shifted Raman scattering. The third potential outcome is that the molecule is already in an excited phonon state, is excited to a higher virtual state, and then relaxes back down to the ground state emitting a photon with more energy than the incident photon; this is called Anti-Stokes Raman scattering. Due to the fact that most molecules will be found in the ground state at room temperature, there is a much lower probability that a photon will be Anti-Stokes scattered. As a result, most Raman measurements are performed considering only the Stokes shifted light.

By further investigating the quantum interpretation of the Raman effect, it can be shown that the power of the scattered light, Ps, is equal to the product of the intensity of the incident photons, Io, and a value known as the Raman cross-section, σR. It can be shown that,

Equation R-9

where λ equals the wavelength of the incident photon. Therefore,

Equation R-10

From equation R-10 it is clear that there is a linear relationship between the power of the scattered light and the intensity of the incident light as well as a relationship between the power of the scattered light and the inverse of the wavelength to the fourth power. Therefore, it would appear that it is always desirable to use a short excitation wavelength and a high power excitation source based on these relationships. However, as we will see in the next section, this is not always the case.

For more :

Be Aware of The DARK WEB !

   

  

         The dark web is the World Wide Web content that exists on darknets, overlay networks that use the Internet but require specific software, configurations, or authorization to access.The dark web forms a small part of the deep web, the part of the Web not indexed by web search engines, although sometimes the term deep web is mistakenly used to refer specifically to the dark web.

The darknets which constitute the dark web include small, friend-to-friend peer-to-peernetworks, as well as large, popular networks like Tor, Freenet, I2P, and Riffle operated by public organizations and individuals. Users of the dark web refer to the regular web as Clearnet due to its unencrypted nature.^[8] The Tor dark web may be referred to as onionland,^[9] a reference to the network's top-level domain suffix .onion and the traffic anonymization technique of onion routing. 

What is the dark web? How to access it and what you'll find

            The dark web is part of the internet that isn't visible to search engines and requires the use of an anonymizing browser called Tor to be accessed.anonymous, and a substantial minority are out to scam others. 

Accessing the dark web requires the use of an anonymizing browser called Tor. The Tor browser routes your web page requests through a series of proxy servers operated by thousands of volunteers around the globe, rendering your IP address unidentifiable and untraceable. Tor works like magic, but the result is an experience that’s like the dark web itself: unpredictable, unreliable and maddeningly slow.anonymous, and a substantial minority are out to scam others. Accessing the dark web requires the use of an anonymizing browser called Tor. The Tor browser routes your web page requests through a series of proxy servers operated by thousands of volunteers around the globe, rendering your IP address unidentifiable and untraceable. Tor works like magic, but the result is an experience that’s like the dark web itself: unpredictable, unreliable and maddeningly slow.

For more watch:

Are you aware.....about IOT

The Internet of things (IoT) is the extension of Internet connectivity into physical devices and everyday objects. Embedded with electronics, Internet connectivity, and other forms of hardware (such as sensors), these devices can communicate and interact with others over the Internet, and they can be remotely monitored and controlled.^[1][2][3][4]

The definition of the Internet of things has evolved due to convergence of multiple technologies, real-time analytics, machine learning, commodity sensors, and embedded systems.^[5] Traditional fields of embedded systems, wireless sensor networks, control systems, automation (including home and building automation), and others all contribute to enabling the Internet of things. In the consumer market, IoT technology is most synonymous with products pertaining to the concept of the "smart home", covering devices and appliances (such as lighting fixtures, thermostats, home security systems and cameras, and other home appliances) that support one or more common ecosystems, and can be controlled via devices associated with that ecosystem, such as smartphones and smart speakers.

The IoT concept has faced prominent criticism, especially in regards to privacy and security concerns related to these devices and their intention of pervasive presence.

When something is connected to the internet, that means that it can send information or receive information, or both. This ability to send and/or receive information makes things smart, and smart is good.

Let’s use smartphones (smartphones) again as an example. Right now you can listen to just about any song in the world, but it’s not because your phone actually has every song in the world stored on it. It’s because every song in the world is stored somewhere else, but your phone can send information (asking for that song) and then receive information (streaming that song on your phone).

To be smart, a thing doesn’t need to have super storage or a super computer inside of it. All a thing has to do is connect to super storage or to a super computer. Being connected is awesome.

In the Internet of Things, all the things that are being connected to the internet can be put into three categories:

1. Things that collect information and then send it.
2. Things that receive information and then act on it.
3. Things that do both.

And all three of these have enormous benefits that feed on each other.

1. Collecting and Sending Information

This means sensors. Sensors could be temperature sensors, motion sensors, moisture sensors, air quality sensors, light sensors, you name it. These sensors, along with a connection, allow us to automatically collect information from the environment which, in turn, allows us to make more intelligent decisions.

(Soil moisture sensor)
Image Credit: Sparkfun

On the farm, automatically getting information about the soil moisture can tell farmers exactly when their crops need to be watered. Instead of watering too much (which can be an expensive over-use of irrigation systems and environmentally wasteful) or watering too little (which can be an expensive loss of crops), the farmer can ensure that crops get exactly the right amount of water. More money for farmers and more food for the world!

Just as our sight, hearing, smell, touch, and taste allow us, humans, to make sense of the world, sensors allow machines to make sense of the world.

2. Receiving and Acting on Information

We’re all very familiar with machines getting information and then acting. Your printer receives a document and it prints it. Your car receives a signal from your car keys and the doors open. The examples are endless.

Whether it’s a simple as sending the command “turn on” or as complex as sending a 3D model to a 3D printer, we know that we can tell machines what to do from far away. So what?

The real power of the Internet of Things arises when things can do both of the above. Things that collect information and send it, but also receive information and act on it.

3. Doing Both

Let’s quickly go back to the farming example. The sensors can collect information about the soil moisture to tell the farmer how much to water the crops, but you don’t actually need the farmer. Instead, the irrigation system can automatically turn on as needed, based on how much moisture is in the soil.

Image Credit: Everything Connects

You can take it a step further too. If the irrigation system receives information about the weather from its internet connection, it can also know when it’s going to rain and decide not to water the crops today because they’ll be watered by the rain anyways.

And it doesn’t stop there! All this information about the soil moisture, how much the irrigation system is watering the crops, and how well the crops actually grow can be collected and sent to supercomputers that run amazing algorithms that can make sense of all this information.

And that’s just one kind of sensor. Add in other sensors like light, air quality, and temperature, and these algorithms can learn much much more. With dozens, hundreds, thousands of farms all collecting this information, these algorithms can create incredible insights into how to make crops grow the best, helping to feed the world’s growing population.

Your Takeaway Definition of IoT

What is IoT?: The internet of Things, or “IoT” for short, is about extending the power of the internet beyond computers and smartphones to a whole range of other things, processes and environments. Those “connected” things are used to gather information, send information back, or both.

Why does IoT matter?: IoT provides businesses and people better insight into and control over the 99 percent of objects and environments that remain beyond the reach of the internet. And by doing so, IoT allows businesses and people to be more connected to the world around them and to do more meaningful, higher-level work.
For further details :