Laser

Heisenberg’s uncertainly principle states that in any simultaneous determination of a pair of complementary variables of a particle, the product of the uncertainties of the variables is greater than and equal to Planck’s constant (h). This note provides us an information on Laser.

Summary

Things to Remember

A laser is a device which produces a highly concentrated monochromatic, coherent and unidirectional beam of light.

The energy states having mean life time of more than 10^-3 sec are known as metastable states.

Achieving more number of atoms in the higher energy state (excited state)than the lower energy state (ground state) is called population of inversion.

The most commonly used solid laser is ruby laser and gas laser is the helium neon gas laser.

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Subjective Questions

Q1:

Write a brief explanation of cardiac profile test.

Type: Long Difficulty: Easy

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Answer: <h4>Cardiac profile</h4>
Analysis of a blood sample can provide important information about the heart. Some of the more significant blood components that may be measured include the following.
Troponin-
Apolipoproteins—the protein component of lipoproteins—are not included in a standard lipid profile, but may be tested separately. Abnormal levels may promote atherosclerosis, and may increase the risk of coronary artery disease (CAD) and stroke.n
CPK(C-reactive protein)-
C-reactive protein (CRP) is a substance that reflects low levels of systemic inflammation and is increased in people at risk for CAD.
CK-MB(cardiac enzyme studies)
Cardiac enzyme studies measure certain enzymes, such as CK-MB, that are released in large amounts when the heart is diseased or damaged, as from a heart attack.
 
Lactate dehydrogenase (LDH)
Is an enzyme that helps the process of turning sugar into energy for your cells to use. LDH is present in many kinds of organs and tissues throughout the body, including the liver, heart, pancreas, kidneys, skeletal muscles, brain, and blood cells.
 
Types of (LDH)-
There are five different forms of LDH, and they are distinguished by slight differences in their structure. Each form of the LDH enzyme is called an isoenzyme.
The isoenzymes of LDH are LDH-1, LDH-2, LDH-3, LDH-4, and LDH-5.
Different LDH isoenzymes are found in different body tissues. The areas of highest concentration for each type of isoenzyme are:
<ul>
<li>LDH-1: heart and red blood cells</li>
<li>LDH-2: white blood cells</li>
<li>LDH-3: lungs</li>
<li>LDH-4: kidneys, placenta, and pancreas</li>
<li>LDH-5: liver and skeletal muscle</li>
</ul>
 
 
 
 
 
 
 
LDH Test-
1.Doctors normally measure LDH levels using a blood draw. Occasionally, doctors may measure LDH levels using urine or cerebrospinal fluid.
2.In adults, a technician draws blood from a vein at the inner elbow or the back of the hand. The technician will clean the test area with an antiseptic and wrap an elastic band around the upper arm to make the vein swell.
3.Then, they will gently insert the needle, and blood flows into a tube. When the tube is full, the technician removes the elastic band and then the needle. A bandage protects the puncture site.
4.In infants or young children, a sharp tool called a lancet may be necessary to take a blood sample. The blood collects in a small tube or on a slide. The technician may place a bandage over the cut. Normally, there is some pain when the needle pierces the skin, and some throbbing afterward.
5.Certain medications and drugs may interfere with an accurate LDH test. Vitamin C (ascorbic acid) may lower LDH levels. Alcohol, anesthetics, aspirin, fluorides, mithramycin, and procainamide may raise LDH levels. Strenuous exercise may also raise LDH levels. Ask your doctor about any medications you should avoid before the test.
 
 
 
 
Aspartate aminotransferase (AST) blood test-
The aspartate aminotransferase (AST) blood test measures the level of the enzyme AST in the blood.
 
Purpose/uses-n
The AST test is commonly used to check for liver diseases. It is usually measured together with alanine aminotransferase (ALT). The AST to ALT ratio can help your doctor diagnose liver disease.
Symptoms of liver disease that may cause your doctor to order an AST test include:
<ul>
<li>fatigue</li>
<li>weakness</li>
<li>loss of appetite</li>
<li>nausea or vomiting</li>
<li>swelling in the abdomen</li>
<li>yellow skin or eyes (jaundice)</li>
<li>dark urine</li>
<li>severe skin itching (pruritus)</li>
</ul>
 
This test may also be ordered for people at high risk of developing liver problems. Some things that increase risk include:
<ul>
<li>exposure to viruses that cause hepatitis</li>
<li>heavy alcohol use</li>
<li>the family history of liver disease</li>
<li>diabetes</li>
<li>being overweight</li>
</ul>
 
 
Normal Results
The normal range is 10 to 34 U
Purpose of cardiac profile test -
Apolipoproteins, homocysteine, and CRP are measured to evaluate the risk of CAD. Cardiac enzymes help to detect the presence of a recent or ongoing heart attack; to determine the timing of a heart attack and assess the degree of damage to the heart muscle; to determine the appropriateness of thrombolytic therapy (a treatment that is beneficial only during an ongoing heart attack); and to monitor any shortage of blood to the heart after cardiac surgery or catheterization.

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Cardiac Profile

Laser

Werner Heisenberg is best known in quantum physics for his discovery of the uncertainty principle, which has the consequence that to make measurements of very short distances — such as those required by string theory — very high energies are required.

The uncertainty principle states that the more precisely you measure one quantity, the less precisely you can know another associated quantity. The quantities sometimes come in set pairs that can’t both be completely measured.

What Heisenberg found was that the observation of a system in quantum mechanics disturbs the system enough that you can’t know everything about the system. The more precisely you measure the position of a particle, for example, the less it’s possible to precisely measure the particle’s momentum.

The degree of this uncertainty was related directly to Planck’s constant — the same value that Max Planck had calculated in 1900 in his original quantum calculations of thermal energy. Heisenberg found that certain complementary quantities in quantum physics were linked by this sort of uncertainty:

Position and momentum (momentum is mass times velocity)
Energy and time

This uncertainty is a very odd and unexpected result from quantum physics. Until this time, no one had ever made any sort of prediction that knowledge was somehow inaccessible on a fundamental level. Sure, there were technological limitations to how well a measurement was made, but Heisenberg’s uncertainty principle went further, saying that nature itself doesn’t allow you to make measurements of both quantities beyond a certain level of precision.

If a coordinate x has an uncertainty Δx ,and if the corresponding momentum component px has an uncertainty Δpx ,then uncertainties are found to be related in general to the inequality,

$$\Delta x\Delta p\geqslant \hslash $$

This is the Heisenberg uncertainty principle for position and momentum.

$$where \; \hslash =\frac {h}{2\pi}$$

The Laser

The LASER stands for “Light Amplification by Stimulated Emission of Radiation”. A laser is a device which produces a highly concentrated monochromatic, coherent and unidirectional beam of light.

Principle of Laser

Suppose that we have an assembly of atoms whose metastable state is $h\mu $. If we somehow raise the atoms to the metastable stable and let a light of frequency $\mu $ fall upon them, there will be more stimulated emission than the stimulated absorption. As a result, we get an amplification of the original light. This is the principle of the laser.

Laser Action

Metastable state

An excited atom cannot stay in excited state for a long time. It comes back to the ground state by emitting a proton. The average time for which the excited atom stays in the excited state is called the mean life time which is characteristics of the energy state. The mean life time for different energy state is different. The energy states having the mean life time of more than 10^-3 sec are known as metastable states.

Spontaneous Emission

An excited atom cannot stay in excited state for a long time. It comes back to the ground state by emitting a proton. If E₁ is the energy in the ground state and E_n is the energy in the n^th state, the frequency of photon emitted when an electron jumps from E_n to E₁ is given by $\mu = \frac {E_n – E_1}{h}$. This kind of emission of photons is known as spontaneous emission.

Stimulated or induced absorption

If the incident photon forces the excited atom E₂ to move the ground state E₁ by emitting the photon of energy $hf = E_2 – E_1$ the emitted photon has the same energy as that of incident photon and they are in the same phase and they move in the same direction as the incident photons. This type of emission is called stimulated emission or induced emission.

Population Inversion

At ordinary room temperature, the number of atoms (N₂) in the excited state (E₂) is much less than the number of atoms (N₁) in the ground state N₁. When light photons of frequency($\mu $)are incident on a large collection of such atoms, the ground state atoms are excited to the excited state (E₂). The excited atoms then return to the ground state either by spontaneous state and stimulated emission. +In order to achieve the higher probability of stimulated emission for laser action the population of the atoms in the excited state must be greater than the population of the atoms in the ground state. Achieving more number of atoms in the higher energy state (excited state)than the lower energy state (ground state) is called the population of inversion.

Types of Laser

Solid laser, the gas laser, semi-conductor laser, chemical laser etc. are types of laser. The most commonly used solid laser is ruby laser and gas laser is the helium-neon gas laser.

Ruby Laser

It consists of a ruby rod whose ends are optically flat surrounded by a glass tube. The glass tube is surrounded by a helical xenon flash tube which acts as the optical pumping system. Ruby rod is a crystal of aluminum oxide (Al₂O₃) doped with 0.05% chromium oxide (Cr₂O₃) so that some of the aluminum atoms in the crystal lattice are replaced by Cr³⁺ ions. The energy level diagram of these chromium ions is as shown in the figure.

Helium-Neon Laser

He-Ne laser tube is approximately 0.5 m long and 5 mm in diameter. The tube is filled with the mixture of the helium and neon gas in the ratio is 5:1 at the total pressure of 1torr. The ends of the tube are cut at Brewster's angle. The tube has two parallel mirrors at its two ends one being partially transparent. The spacing of the mirrors is equal to an integral number of half wavelengths of the laser height. There are two electrodes which are connected to power supply. The mixture of gas is ionized by passing the electric current through it.

Uses of Laser

The laser is used in radio communication in outer space.
It is used in welding and perching holes in metals.
It is used in detecting and ranging objects at great distances.
It is used in medicine and scientific research.

Properties of Laser

The light is very nearly monochromatic.
The laser beam diverges hardly at all.
The lights are coherent and are in phase with each other.
The beam is extremely intense.

References

Manu Kumar Khatry, Manoj Kumar Thapa, etal. Principle of Physics. Kathmandu: Ayam publication PVT LTD, 2010.

S.K. Gautam, J.M. Pradhan. A text Book of Physics. Kathmandu: Surya Publication, 2003.

Lesson

Quantisation of Energy

Subject

Physics

Grade

Grade 12

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