14435_PHY 803 Unit 10

7/28/2019 14435_PHY 803 Unit 10

1/14

LPU/PHY 803/Laser Technology Autumn Term 2012-13

Class room presentations for internal use in LPU only

Measurement of thermal constants with laser

Lasers are clean heat sources which quick start

and stop

Rapid heat and cooling

Hence can be used for the measurement of thermal

constants

K, (W, cmoC) thermal conductivity , .

C (J/ gm oC) heat capacity

It is the measure of amount of heat that can be

stored in a solid.

Thermal Diffusivity (k) = K/rC

7/28/2019 14435_PHY 803 Unit 10

2/14

7/28/2019 14435_PHY 803 Unit 10

3/14



Experimental arrangement

Results are obtained fast

One measurement per

laser pulseInsulators/building

materials for better energy

saving

(k) = K/rC relation canbe used to calculate

othe constants

7/28/2019 14435_PHY 803 Unit 10

4/14



Metallurgical effects

Rapid heating and cooling rates by laser pulses106oC/sec to 1010oC/sec

Results in the formation of new metallurgical

phasesThis development of new metallurgical

phases/dislocations On treatment with laser

pulses are termed laser metallurgical effects.This gives a powerful tool to study new phases

in very very short time.

7/28/2019 14435_PHY 803 Unit 10

5/14



Metallurgical effects contd.

Examples1. New phase of Fe-C was discovered by laser

treatment

2. Thermal etching in materials like Cu3. Study of dislocations in almumium

4. And so on

7/28/2019 14435_PHY 803 Unit 10

6/14



Pulsed laser deposition (PLD)

7/28/2019 14435_PHY 803 Unit 10

7/14



PLD contd.

Diamond,

Al2O3 ,

coatings

7/28/2019 14435_PHY 803 Unit 10

8/14



PDL contd.Advantages

(i) Superior adhesion and reduced stress result from a

metallurgical bond between the diamond and substrate.

(ii) The process is carried out in atmosphere, without the

restrictions of a vacuum chamber.(iii) Almost any size or shape can be coated by controlling

movements of the lasers or work-piece.

(iv) Pre-treatment and/or preheating of the substrate is

not required, permitting coating substrate of as-

manufactured components and elimination of wet

chemistry pre-treatment.

7/28/2019 14435_PHY 803 Unit 10

9/14



PDL advantages Contd.

(v) Only carbon dioxide is used as a primary / secondarysource for carbon with nitrogen acting as a shield and

possible stockpiling process ingredient. This replaces the

use of dangerous gases such as hydrogen and methane,

critical ingredients in the CVD process.

(vi) Deposition rates are dramatically increased, with

linear growth rates exceeding 1 micron per second as

opposed to 1 to 5 microns per hour by CVD.

(vi) The process can be applied to almost any substratesuch as stainless steel, high-speed steel, iron, plastic, glass,

copper,aluminum, titanium and silicon.

7/28/2019 14435_PHY 803 Unit 10

10/14



Crystal growth

Crystal growth techniques

1. Solution Growth

2. Growth from the melt

3. Growth from vapourThe fundamentals are relatively simple but the

interactions involved and the individuality of the

different materials are so complex that theoretical

predictions have met with very limited success.

Crystal growth is an art

7/28/2019 14435_PHY 803 Unit 10

11/14


Typical LHPG setup CO2 laser

Pulling

mechanism

Sample rod pushing

mechanism

Focusing mirrors

Sample rodHe-Ne laser for alignment

7/28/2019 14435_PHY 803 Unit 10

12/14



Typical growth (material LAP)

7/28/2019 14435_PHY 803 Unit 10

13/14


Melt

Initial growth

Final fiber

Typical growth contd. (material LiNbO3)

Feed rod

7/28/2019 14435_PHY 803 Unit 10

14/14



Advantages

1. Very less time consuming; hours compared todays in case non-laser techniques

2. As long as material absorbs the laser radiation

no max temperature limit

3. Rapid quenching

4. Less material required

14435_PHY 803 Unit 10

Documents

Transcript of 14435_PHY 803 Unit 10