- Lasers were invented in 1958 based on earlier work by Einstein and others on stimulated emission of radiation.
- A laser works by stimulating electrons in an excited state to emit photons coherently and in phase through a process called stimulated emission, which requires a population inversion where more atoms are in an excited state than a ground state.
- Laser light has three unique properties: it is highly monochromatic, directional, and coherent, unlike ordinary light. These properties allow lasers to deposit energy in a small area.
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The term "laser" originated as an acronym for "light amplification by stimulated emission of radiation"
Lasers have many important applications. They are used in common consumer devices such as DVD players, laser printers, and barcode scanners. They are used in medicine for laser surgery and various skin treatments, and in industry for cutting and welding materials. They are used in military and law enforcement devices for marking targets and measuring range and speed. Laser lighting displays use laser light as an entertainment medium. Lasers also have many important applications in scientific research
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The term "laser" originated as an acronym for "light amplification by stimulated emission of radiation"
Lasers have many important applications. They are used in common consumer devices such as DVD players, laser printers, and barcode scanners. They are used in medicine for laser surgery and various skin treatments, and in industry for cutting and welding materials. They are used in military and law enforcement devices for marking targets and measuring range and speed. Laser lighting displays use laser light as an entertainment medium. Lasers also have many important applications in scientific research
Final project report on grocery store management system..pdfKamal Acharya
In today’s fast-changing business environment, it’s extremely important to be able to respond to client needs in the most effective and timely manner. If your customers wish to see your business online and have instant access to your products or services.
Online Grocery Store is an e-commerce website, which retails various grocery products. This project allows viewing various products available enables registered users to purchase desired products instantly using Paytm, UPI payment processor (Instant Pay) and also can place order by using Cash on Delivery (Pay Later) option. This project provides an easy access to Administrators and Managers to view orders placed using Pay Later and Instant Pay options.
In order to develop an e-commerce website, a number of Technologies must be studied and understood. These include multi-tiered architecture, server and client-side scripting techniques, implementation technologies, programming language (such as PHP, HTML, CSS, JavaScript) and MySQL relational databases. This is a project with the objective to develop a basic website where a consumer is provided with a shopping cart website and also to know about the technologies used to develop such a website.
This document will discuss each of the underlying technologies to create and implement an e- commerce website.
Vaccine management system project report documentation..pdfKamal Acharya
The Division of Vaccine and Immunization is facing increasing difficulty monitoring vaccines and other commodities distribution once they have been distributed from the national stores. With the introduction of new vaccines, more challenges have been anticipated with this additions posing serious threat to the already over strained vaccine supply chain system in Kenya.
Immunizing Image Classifiers Against Localized Adversary Attacksgerogepatton
This paper addresses the vulnerability of deep learning models, particularly convolutional neural networks
(CNN)s, to adversarial attacks and presents a proactive training technique designed to counter them. We
introduce a novel volumization algorithm, which transforms 2D images into 3D volumetric representations.
When combined with 3D convolution and deep curriculum learning optimization (CLO), itsignificantly improves
the immunity of models against localized universal attacks by up to 40%. We evaluate our proposed approach
using contemporary CNN architectures and the modified Canadian Institute for Advanced Research (CIFAR-10
and CIFAR-100) and ImageNet Large Scale Visual Recognition Challenge (ILSVRC12) datasets, showcasing
accuracy improvements over previous techniques. The results indicate that the combination of the volumetric
input and curriculum learning holds significant promise for mitigating adversarial attacks without necessitating
adversary training.
Student information management system project report ii.pdfKamal Acharya
Our project explains about the student management. This project mainly explains the various actions related to student details. This project shows some ease in adding, editing and deleting the student details. It also provides a less time consuming process for viewing, adding, editing and deleting the marks of the students.
Overview of the fundamental roles in Hydropower generation and the components involved in wider Electrical Engineering.
This paper presents the design and construction of hydroelectric dams from the hydrologist’s survey of the valley before construction, all aspects and involved disciplines, fluid dynamics, structural engineering, generation and mains frequency regulation to the very transmission of power through the network in the United Kingdom.
Author: Robbie Edward Sayers
Collaborators and co editors: Charlie Sims and Connor Healey.
(C) 2024 Robbie E. Sayers
Industrial Training at Shahjalal Fertilizer Company Limited (SFCL)MdTanvirMahtab2
This presentation is about the working procedure of Shahjalal Fertilizer Company Limited (SFCL). A Govt. owned Company of Bangladesh Chemical Industries Corporation under Ministry of Industries.
COLLEGE BUS MANAGEMENT SYSTEM PROJECT REPORT.pdfKamal Acharya
The College Bus Management system is completely developed by Visual Basic .NET Version. The application is connect with most secured database language MS SQL Server. The application is develop by using best combination of front-end and back-end languages. The application is totally design like flat user interface. This flat user interface is more attractive user interface in 2017. The application is gives more important to the system functionality. The application is to manage the student’s details, driver’s details, bus details, bus route details, bus fees details and more. The application has only one unit for admin. The admin can manage the entire application. The admin can login into the application by using username and password of the admin. The application is develop for big and small colleges. It is more user friendly for non-computer person. Even they can easily learn how to manage the application within hours. The application is more secure by the admin. The system will give an effective output for the VB.Net and SQL Server given as input to the system. The compiled java program given as input to the system, after scanning the program will generate different reports. The application generates the report for users. The admin can view and download the report of the data. The application deliver the excel format reports. Because, excel formatted reports is very easy to understand the income and expense of the college bus. This application is mainly develop for windows operating system users. In 2017, 73% of people enterprises are using windows operating system. So the application will easily install for all the windows operating system users. The application-developed size is very low. The application consumes very low space in disk. Therefore, the user can allocate very minimum local disk space for this application.
2. LASERS
History of the LASER
• Invented in 1958 by Charles Townes (Nobel prize
in Physics 1964) and Arthur Schawlow of Bell
Laboratories
• Was based on Einstein’s idea of the “particlewave
duality” of light, more than 30 years earlier
• Originally called MASER (m = “microwave”)
4. What is Laser?
Light Amplification by Stimulated
Emission of Radiation
•A device produces a coherent beam of optical
radiation by stimulating electronic, ionic, or
molecular transitions to higher energy levels
•When they return to lower energy levels by
stimulated emission, they emit energy.
5. Properties of Laser
5
The light emitted from a laser is monochromatic, that is, it is of one
color/wavelength. In contrast, ordinary white light is a combination of many
colors (or wavelengths) of light.
Lasers emit light that is highly directional, that is, laser light is emitted as
a relatively narrow beam in a specific direction. Ordinary light, such as
from a light bulb, is emitted in many directions away from the source.
The light from a laser is said to be coherent, which means that the
wavelengths of the laser light are in phase in space and time. Ordinary
light can be a mixture of many wavelengths.
These three properties of laser light are what can make it more
hazardous than ordinary light. Laser light can deposit a lot of energy
within a small area.
12. Spontaneous Emission
•The atom decays from level 2 to level 1 through the
emission of a photon with the energy hv. It is a
completely random process.
13. Stimulated Emission
atoms in an upper energy level can be triggered or
stimulated in phase by an incoming photon of a
specific energy.
14. Stimulated Emission
The stimulated photons have unique properties:
•In phase with the incident photon
•Same wavelength as the incident photon
•Travel in same direction as incident photon
15. Population Inversion
•A state in which a substance has been energized, or
excited to specific energy levels.
•More atoms or molecules are in a higher excited state.
•The process of producing a population inversion is
called pumping.
•Examples:
→by lamps of appropriate intensity
→by electrical discharge
16. Pumping
•Optical: Uses flashlamps and high-energy light sources (Ruby
Laser)
•Electrical Discharge: application of a potential difference across
the laser medium (He-Ne Laser)
•Inelastic Collisions between Atoms: Atoms exchange energies
with other by in-elastic collisions and gets excited due to
additional absorbed energy. (He-Ne Laser)
•Direct Conversion: Electrical energy is directly converted into
optical energy as LASER beam (Gallium Arsenide
semiconducting Laser)
•Chemical Reaction: Many exothermic reactions provide
essential energy for pumping of atoms.
18. E1
E2
• n1 - the number of electrons of energy E1
• n2 - the number of electrons of energy E2
•Population inversion-
n2>>n1
2 2 1
1
( )
exp
n E E
n kT
Boltzmann’s equation
example: T=3000 K E2-E1=2.0
eV
4
2
1
4.4 10
n
n
19. Resonance Cavities
and Longitudinal Modes
Since the wavelengths involved with lasers and
masers spread over small ranges, and are also
absolutely small, most cavities will achieve
lengthwise resonance
Plane
parallel
resonator
Concentric
resonator
Confocal
resonator
Unstable
resonator
Hemispheric
al resonator
Hemifocal
resonator
c
c
f
f
c: center of curvature, f: focal point
L = nλ
20. Transverse Modes
TEM00:
I(r) = (2P/πd2)*exp(-2r2/d2)
(d is spot size measured
to the 1/e2 points)
Due to boundary conditions and
quantum mechanical wave
equations
21. Einstein’s coefficients
Probability of stimulated absorption R1-2
R1-2 = r (n) B1-2
Probability of stimulated and spontaneous emission :
R2-1 = r (n) B2-1 + A2-1
assumption: n1 atoms of energy e 1 and n2 atoms of energy e 2 are in thermal
equilibrium at temperature T with the radiation of spectral density r (n):
n1 R1-2 = n2 R2-1 n1r (n) B1-2 = n2 (r (n) B2-1 + A2-1)
2 1 2 1
1 1 2
2 2 1
/
=
1
A B
n B
n B
r n
E1
E2
22. B1-2/B2-1 = 1
According to Boltzman statistics:
r (n) = =
1
2 1
2
exp( ) / exp( / )
n
E E kT h kT
n
n
1
)
exp(
/
1
2
2
1
1
2
1
2
kT
h
B
B
B
A
n 1
)
/
exp(
/
8 3
3
kT
h
c
h
n
n
3
3
1
2
1
2 8
c
h
B
A n
Planck’s law
23. The probability of spontaneous emission A2-1 /the probability of
stimulated emission B2-1r(n :
1. Visible photons, energy: 1.6eV – 3.1eV.
2. kT at 300K ~ 0.025eV.
3. stimulated emission dominates solely when hn /kT <<1!
(for microwaves: hn <0.0015eV)
The frequency of emission acts to the absorption:
if hn /kT <<1.
1
)
/
exp(
)
(
1
2
1
2
kT
h
B
A
n
n
r
1
2
1
2
1
2
1
2
2
1
1
1
2
2
1
2
2 ]
)
(
1
[
)
(
)
(
n
n
n
n
B
A
B
n
B
n
A
n
x
n
r
n
r
n
r
x~ n2/n1
24. Condition for the laser operation
If n1 > n2
• radiation is mostly absorbed absorbowane
• spontaneous radiation dominates.
• most atoms occupy level E2, weak absorption
• stimulated emission prevails
• light is amplified
if n2 >> n1 - population inversion
Necessary condition:
population inversion
E1
E2
25. How to realize the population inversion?
Thermal excitation:
2
1
exp
n E
n kT
Optically,
electrically.
impossible.
The system has to be „pumped”
E1
E2