Unique properties of LASERs and their applications


Hello and a very good morning. Wherever you are, let me welcome you to this
course whose title is ‘Laser Fundamentals and Applications’. This is 20 hours course and this course is
basically intended for undergraduates or those people who want to learn the basic of fundamentals
of lasers and their applications. But nevertheless those people who already
have some basic idea about laser, this course can benefit them as well, because toward the
later part of this course we would like to cover certain applications. Some of them will be state of the art applications
which are quite advanced in nature. There will be food for everyone pretty much. Today is the first day of this lecture series,
and let us start this topic by asking the very fundamental question, that is, why we
should study laser, why should anyone study laser. The question that we asked first, ‘why Laser?’ Now laser is probably the one of the most
important inventions of the last century, if not the most important invention. When I say that, that pretty much answers
why one study the laser should. If I want to answer it little bit more explicitly,
then what I should say is, the answer is that, it is important to study because of its unique
properties. Unique properties of Laser
Laser leads to very unique applications. Anything, any invention or discovery becomes
really important when it actually leads to certain applications in practical life or
in real life, then people like to know more about that particular topic or the particular
thing. When it is said that the laser has unique
properties, so, what kind of unique properties? We will talk about those properties in greater
detail as we progress, but let me tell you a very few things. When I talk about these unique properties,
we can name a few. First is, this laser light has a property
which is called monochromaticity. That is the, you know, laser light has a very
very narrow linewidth. If I look at the spectrum of any laser output,
it will be really narrow. That is called a monochromatic radiation or
near-monochromatic radiation. So, depending on what kind of laser one is
looking at, one can get a really monochromatic radiation, which is a big advantage if you
want to do certain kind of applications, be it a of fundamental type or be it practical
real life application. Second thing is that laser light is coherent
in nature. When I say this term coherent that means that
all the photons coming out from laser has the same phase. All the photons when they have same phase,
or they are in phase, we call that light beam as a coherent beam. This is a huge advantage which is not available
in all other light devices that gives different types of light – different wavelengths of
light, different frequencies of light. But laser gives rise to this coherent beam. The laser gives a light we often call laser
beam. Why? Because, this comes out like a colimated beam. The laser lights are colimated, moreover they
have directionality. They can be highly tunable, meaning that I
can start from one particular wavelength, and I can go to a different wavelength, and
I can scan through a huge range. So, this is called tunability; this tunability
is a huge advantage for any light source. Another most important property of these lasers
is that they can have really high power. The energy density of the laser beam is extremely
high. There are different terms used for that. One can use a term called fluence, which measures
the power of the laser beam. One can have a very high power average power,
or there is something called peak power which we will discuss more and more in detail. These lasers can be having really large or
high power which can be used in different industrial applications like one can use it
for cutting or welding or melting various different materials. These are certain unique properties of this
laser, and as you can understand that if some light coming out from some device due to certain
processes have these particular set of properties, they can be used in various different things. Now when I say that it can be applied to various
different sectors what do I mean? How wide is the range of applications? Let us look at that. So, let us name a few of the applications. So, Applications of Laser. Now, laser can be applied in various different
sectors as I said earlier. For example, it can be used in a scientific
application, it can be used in medical science or medicine, it can be used
in industry or commercial purposes, it can have application in defense. There are many more different sectors than
we can name. Essentially, if you think of any particular
area where you look for an application of a device, laser is a device which can probably
find application in all those areas. So, this is so versatile. Let me give you a bit glimpse about what are
the different types of applications in all these sectors like in a scientific sector,
or medical science, in industry, or in military science, what are the different types of application
that one can achieve using lasers. So, first let us talk about the Scientific
Applications. So, there are varieties, types of scientific
projects where laser can find its applications. Let us first start with something called Spectroscopy. Most of you perhaps know what spectroscopy
is. It is a subject area where it deals with light-matter
interaction. This particular topic can give information
about molecules and materials, their structures, their properties, and various other things. Now there are various different kinds of spectroscopy,
and lasers find their applications in pretty much all the different types of spectroscopy
that you can think of, except a very few. One of the largest contributions of lasers
in this domain of spectroscopy is probably the Nonlinear Optics, where people generate
newer frequencies by combination of different input frequencies. We will talk about nonlinear optics in quite
detail at a later part. And, we have Raman Spectroscopy. We know Raman process is a very weak interaction
of light with matter and you need a really high intensity light source to obtain Raman
Spectra. So, lasers have make Raman Spectroscopy really
easy in that sense, because it can provide a really high intensity of light. There is something called laser induced breakdown
spectroscopy (LIBS). Various super resolution spectroscopies can
be obtained using laser. Why? Because earlier we mentioned that it can be
really a monochromatic light source. So, if I want to have a very specific transition
from one state to another in a particular molecule, I need to have a specific frequency
of light or specific wavelength of light, and that can be achieved using laser, using
a high monochromatic beam. So, Super-resolution spectroscopy
can be achieved using laser. Various different Interferometric techniques
can find laser applications. So, if I think about microscopy or imaging,
if I talk about microscopy and imaging, today’s microscopy, particularly optical microscopy,
cannot be thought without the use of laser in it. So, you will name any optical microscopy,
laser is used. If you talk about confocal microscopy, you
need lasers. You want to have multiphoton microscopy, you
definitely need laser. Without laser you cannot have multiphoton
microscopy. And many of you may be aware that multi photon
microscopy is one of the wonderful today’s tools. Today people use that in biology, medicine,
material science, and where not. The latest Nobel Prize in the field of optics
and microscopy went to William Moerner, Stefan Hell, and Eric Betzig. They got this Nobel Prize because of the invention
of super resolution microscopy. The super resolution microscopy or imaging
could not be achieved without having the laser in hand. So, ‘super resolution’, when we called
super resolution microscopy here, it essentially points to the spatial resolution, that is
how you can separate two points in space which
are very close enough. You know, if you can resolve two points in
space, then you have a certain resolution. Now if I bring these two points very close
to each other you may not be able to resolve that and two points may appear to be a single
point. Now, if you have a technique which can give
you the ability to resolve, even that extremely closely spaced points, you are essentially
achieving something called super resolution. This is a very gross way of saying this. We will talk about it in detail then we will
explain what super resolution technique is. And there are other microscopic techniques
which are being used very often in industry and particularly medical industry, called
optical coherence tomography. You need a laser to do that. There are other areas in scientific research
where without laser you cannot do much. So, what are those areas? If we can start looking at that, if you talk
about Astronomy you have laser applications. Astro physics, Geology, Seismology, Space-technology,
Remote-sensing – where you find application of lasers in a
particular way, in terms of LIDAR. Lasers are used to do a particular form of
cooling; cooling of atoms and molecules which is called laser cooling. Of course, you can understand without a laser
you cannot have laser cooling and this is of paramount importance in certain research
areas. There are certain other areas like Nuclear
Fusion where laser is being used now. So, you know that nuclear fusion requires
a very high amount of energy. Laser as we said can provide very high power
light beam, and this high power light beam, if it is concentrated, one can actually produce
a huge amount, rather humongous amount of energy, which can even lead to nuclear fusion. So, you can guess that how vast is the laser
application. And, I have just talked about a few topics
under scientific research where laser finds its application every now and then. Basically if I tell you the truth, without
lasers most of these scientific topics would not be possible to deal with. Now if I look into the application of lasers
in the field of medical science or medicine, so – Medical application what you can think
of? Many of you probably know, many of your relatives,
parents, or teachers, friends might be telling you that – I have gone through a laparoscopy. These laparoscopic surgeries are also assisted
by lasers. So, in first place, there are, number of different
surgeries that are done by laser or assisted by lasers. If we name a few, eye surgery is regularly
done using laser. So, many people come and tell you that we
have done this cataract operation, cataract surgery. How did they do it? They say ‘Oh, we did through Lasik’. What is Lasik? This is a laser assisted process. So, there are other types of surgeries that
you can do with laser. Very regularly which it is done, that is,
soft-tissue surgery, in many times, many occasions. So, people have troubled ligament or tendons
and all of these are operated using lasers. There are various Endoscopic surgeries that
are done using laser. Actually as a matter of fact, this endoscopy
process itself is done through laser, it is assisted by laser, and if you are going to
do endoscopic surgery, many occasions you do it by using laser. It is almost a kind of non invasive process
and you do it little bit from outside. There are different other things, like I mentioned
about non invasive technique, regarding dermatology. Now a day, most of the dermatology treatments
are done through laser. So, in dermatology you find laser application. As I mentioned in the very first minute of
this slide, laparoscopy is done using lasers. There is something called Photodynamic therapy. This is particularly used in case of removing
or killing tumors or malignant cells like cancer cells. You use laser light to do the job. We might touch upon this particular part of
photodynamic therapy during the application part when we will talk about the applications. There are many other types of applications
in medical science. We are not going to talk about everything. What I am trying to do in this first class
is, to give you a glimpse of the areas where this can be applied, and some of this we will
discuss in detail. If we talk about industrial, so, Industry
or Commercial applications, you take simplest thing that you use every day, you find applications
of laser. You take print out of your papers or picture,
anything. What do you use? You use a laser scanner. You read or write data in optical devices
like CD – DVD. There what you use, you use a laser to do
the job. So, these storing of data and retrieving it
from that particular device is done by laser. So, we use it in CD-DVD, in these optical
drives, storage devices. You use it in reading the barcodes. Whenever you go to a market or a mall and
you buy some stuff, shop owner will scan some area of the product where there will be some
bars which contains the information regarding price and other things, and that barcode is
scanned by using laser. These are very simple things that you come
across every day. There are various other things that you may
know where laser is used. In machining industry or, you know, in engineering
works, people need to cut, and weld, or peen metals, in a large scale. So, in steel industry, in railways industry,
you need to do cutting, and welding, peening, soldering, joining, and various different
things. So, in every, you know, each and every process
that I just mentioned, for example, like cutting, welding, joining, and then peening, soldering
– these are certain process which metallurgists use every now and then. In industry these are done in a large scale. And all these processes can be done using
lasers. So, there are now terms called laser cutting,
laser welding, laser peening, and so on. There are other types of processes where laser
is regularly used. As you know, cladding, drilling, and so on. You know, in case of macro machining or macro
material processing, and even in micro material processing or micro machining, laser is very
regularly used. They are used in additive manufacturing every
now and then. There are certain other aspects which are
very very important for industry, particularly in space industry. There is something called power beaming. So, what is this power beaming? For the spacecraft, this power beaming through
laser is a possible solution to transfer energy to the climber of a space elevator. So, you can imagine how important role that
plays in the space industry itself. Then, apart from these ones, if you open any
commercial website today, you will see there are various controlling devices, particularly
remote controlling devices. There you find the application of lasers. So, laser is used in the remote sensing devices
which are based on optical sensing mechanism. Apart from remote sensing, there are various
other different types of detectors or sensors where laser is used. Another important area that many of you might
be aware of, is the area of optical communication, where you need laser. Apart from that, on a lighter note, whenever
you see some party going on or any musical program, you see something like laser show
or laser display, and nowadays it is so common. Now just think about there is no laser, so
there is no laser show. I can go on and on to tell you what are the
different areas where laser have their functions. There is another important area which I will
just mention, that is in the area of defense or the military applications. Laser is being used
as ammunition; it is used to destroy, objects, or the weapon. So, it is being used as a weapon. Apart from that, the defense industry use
laser to sense or detect traits coming in different forms that can be a missile or that
can be some intrusion at the border. So, in all these cases laser is used either
to detect the trait or to eliminate the trait. In military industry usage of laser has gone
up like super exponentially. We will not talk about military applications
that much. So, by now I guess you are convinced that
laser really has a vast application in various different sectors in your day to day life
everywhere. If something has such a wide application,
applicability, it would be wise to know at least the basic things about that particular
topic or that particular device. In our case that is laser. So, we at least need to know something about
this laser and that is exactly what is our aim in this particular course – to learn some
basics of this laser and to know about certain applications that this laser can have. So, with this, I will conclude today’s class
and we will meet in the following class with something about the history of laser and some
other staffs. Thank you very much.

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