second harm gen

Question 1

Assumptions made here

Answer 1

Lossless medium at freq w1 and w2
X2 possessly full permutation symmetry as a result of this
slowly varying amplitude approx
typically assume no second harm light is incident on the medium A2(z=0) = 0

Question 2

phase matching condition for second harm gen

Answer 2

2k1 = k2

Question 3

what is the undepleted pump apporx result
Second hard gen

Answer 3

Here A1 the pump at freq w1 reamins constant
DEs simpler to solve
fraction of total power oscillates as a function of distnace complimentarily between w1 and w2 (always sum to total power 1, full conversion)

Question 4

Diff freq generation process

Answer 4

strong pump beam w3 (Assume constant)
weaker, later amplified signal beam w1
produced idler strong at w2 =w3-w1 (initially zero)

Question 5

Important distinction betweem sim and difference freq generation

Answer 5

In sum freq -> Upconversion
- oscillatory behavior w3 = w1(weak) + w2 (strong)
- due to anhilation of w2 IR weak beam for each phtoon w3 signal created

In diff freq -> Signal and idler (we only looked at perfect phase matching)
w2 (initially none) = w3 (Strong pump) -w1(weak signal)
- NO OSCILLATIONS
- monotonic growth for w2 AND w1
- signal gets amplified not depleted
Reason: presence of w2 stimulates production of w1 by diff freq generation and they actively feed each other (not feed off of each other)

Question 6

ANother word for diff freq generators

Answer 6

Parametric ampliefiers
since the proccess of DFG NECESSRILY leads to the amplification of the lower freq input field

Question 7

What is phase matching on a microscopic level

Answer 7

wehn individual atomic dipoles in a medium are well phased such that their emitted radaiton from each dipole adds up coherently in the forward direction

Question 8

anomalous dispersion

Answer 8

-extremely pronounced near an absorption feature of a material
- where refractive index DEcreases with increasign freq

Question 9

how is phase atching commonly achieved in crystals

Answer 9

Crystals exhibit birefringence and so their refractive index dep on polarisation of light.

light can experience an extraodinary n_e or ordinary index of refraction n_o

type I and II phase matching

Question 10

limit of opto electronic devices to detect pulse widths

Answer 10

tens of ps

Question 11

autocroeelation means:

Answer 11

the pulse investigated is compared with a time delayed copy of itself

as opposed to cross correlation where it would be compared to a different pulse

Question 12

GVD

Answer 12

the frequency dependence of the group velocity in a medium
-a characteristic of a dispersive medium, used most often to determine how the medium will affect the duration of an optical pulse traveling through it.
-a pulse travelling through a mediium with high GVD will eventually be broadened

Question 13

Active mode locking e.g

Answer 13

AOM - acousto optical modulator inserted into the laser cavity close to an end mirror

• this is a loss modulator producing a time dependent refractive index (and thus loss) modulator
• produces side bands next to the main frequency band. tune the AOM st the side bands overlap wiht th eadjacent resonating frequencies to mode lock

Question 14

relation ot mode spacing and cavity length in a resonatating cavity

Answer 14

df = c/2L
L is the cavity length and df is the freq spacing

1/time= freq = speed/dist

Question 15

pulse stretcher anad compressor

Answer 15

stretcher, pusle is lengthened by positive GVD medium and vice veresa for compressor

Question 16

what does GVD mean qualitativly

Answer 16

+GVD: the red sepctral components of the pusle experinece shorter optical path length than blue

for -GVD: