Resonance enhancement of two-photon cross-section for optical storage in the presence of hot

band absorptionN. Makarov, A. Rebane, M. Drobizhev, D. Peone

(Department of Physics, Montana State University, Bozeman, MT 59717, USA)

H. Wolleb, H. Spahni(Ciba Specialty Chemicals Inc, P.O. Box Ch-4002 Basle,

Switzerland)E. Makarova, E. Luk’yanets

(Organic Intermediates and Dyes Institute, Moscow, Russia)

Outline

• Principles of 3D 2PA optical memory

• 2PA-sensitive photochromes

• Resonance enhancement

• 2PA vs. 1PA

• 2PA in phthalocyanines

• Summary

Principles of 3D 2PA optical memory

hv

dv

hh dh

write

form Bform A

M

L

L

read

form Bform A

PD

DM

L

L

Need for 2PA-sensitive photochromes

2

2 2 4 2 2max 0

8( )A B

A B F

SNR

I N NA

Access with 1 pulse: 100fs, 100MHz => 1TB read/write in 24 hrsEach bit have to be written and read by only 1 femtosecond pulse!

11 2 30max 2

90

10 / 10

~ 750 800

~ 100

~ 10

~ 0.1

~ 0.1

~ 0.1

~ 0.5

A B

F

photonsI W cm

cm snm

fs

N molecules

NA

3 42 10 10 GM

32 10off resonance GM

4

2 2

2 22

2 22

5off resonance

fg fg PA

Lg

hnc

μ Δμ

Compound 1, cm2 (, nm) 2,GM (, nm) F AB

Fulgide-based 3.3810-16 (650) 2 (780) 0.16 0.045

Spiropyrans-based 8.2710-18 (352) 100 (694) 0.05 0.01

Diarylethene-based 1.3310-16 (530-600)

600 (410) 0.5 0.4

2PA resonance enhancement

2 24 2

2 22 2 2

2 22

5

ig fi

PA

ig m

Lg

hnc

μ μ

A fundamental trade-off between 2PA and 1PA:• tune laser frequency as close as possible to the resonance• tune as far as possible to decrease 1PA background

2

1

2

2 2 0

2

2

wPAwPA

w rPA PA F A B

PSBR

P M

NASNR P P N

15000 14000 13000 12000 11000 10000 9000

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

700 800 900 1000 1100Wavelength, nm

2,

GM

Frequency, cm-1

NN

NH NH

N

NN N

O

O

O

Qx(A)Qy(A)

long wavelength tail region

2PA vs. 1PA

1 2 3 4 5 6 7 8 9

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

900 nm, a=2.14 ±0.16 890 nm, a=1.99 ±0.05 880 nm, a=1.68 ±0.04 870 nm, a=1.54 ±0.09 860 nm, a=1.36 ±0.10 850 nm, a=1.24 ±0.17

Flu

ore

sce

nce

inte

nsi

ty,

a.u

.

Laser pulse energy, a.u.

I(P)= Pa

Power dependence of the fluorescence signal

Absorption spectra at different temperatures as

calculated from fluorescence spectrum

10-4

1

Ab

sorb

an

ce,

a.u

.

0 500 1000 1500 2000 2500

10-3

10-1

10-5

10-2

Frequency detuning 1PA-L, cm-1

240K

300K

Fluorescence 240K

850-900 nm

900nm

850nm

860nm

870nm

880nm

890nm

2PA-sensitive phtalocyanines

3NN

NH NH

N

NN N

O

O

O

O

OH

NN

NH NH

N

NN N

O

O

O

1NN

NH NH

N

NN NBut

But

But

2 4NN

NH NH

N

NN N

O

O

O

O

O

NN

NH NH

N

NN N

O

O

O

O

O

O

5 6NN

NH NH

N

NN N

O

O

O

O

300 400 500 600 700 8000.01

0.1

1

10

100

1000

102

103

104

105

106

10735000 30000 25000 20000 15000

2, G

M

Wavelength, nm

Molecule 3, 1PA: Endo Exo Mix

2PA: Endo Exo Mix

, M

-1cm

-1

Frequency, cm-1

QxQy

300 400 500 600 700 8000.01

0.1

1

10

100

1000

102

103

104

105

106

10735000 30000 25000 20000 15000

2, G

M

Wavelength, nm

Molecule 2: 1PA 2PA

, M

-1cm

-1

Frequency, cm-1

QxQy

300 400 500 600 700 8000.01

0.1

1

10

100

1000

35000 30000 25000 20000 15000

102

103

104

105

106

107

Molecule 1, 1PA: a b

2PA: a b

, M

-1cm

-1

Frequency, cm-1

2, G

M

Wavelength, nm

QxQy

300 400 500 600 700 8000.01

0.1

1

10

100

1000

35000 30000 25000 20000 15000

102

103

104

105

106

107

2, G

M

Wavelength, nm

Molecule 4, 1PA: Endo Exo

2PA: Endo Exo

Frequency, cm-1

, M

-1cm

-1

Qx+Qy

300 400 500 600 700 8000.01

0.1

1

10

100

1000

35000 30000 25000 20000 15000

102

103

104

105

106

107

2, G

M

Frequency, cm-1

Wavelength, nm

, M

-1cm

-1

Molecule 6, 1PA: a) Endo a) Exo b) Endo b) Exo

2PA: a) Endo a) Exo b) Endo b) Exo

Qy Qx

300 400 500 600 700 8000.01

0.1

1

10

100

1000

35000 30000 25000 20000 15000

102

103

104

105

106

107

2, G

M

Wavelength, nm

Molecule 5, 1PA: Endo Exo Mix

2PA: Endo Exo Mix

, M

-1cm

-1

Frequency, cm-1

Qx

Qy

2PA-sensitive phtalocyanines

Compound , M-1cm-1 Qx, nm Qy, nm 2(2Qx), GM 2

(2Qy), GM

1 111000 758 709 0.34 2.7

2 120000 729 686 0.16 1.8

3 141000 742 712 0.40 1.0

4 113000 727 - 0.52 -

5 152000 739 711 0.51 1.2

6 113000 757 715 0.55 3.4

1) The change of substituents from butyl groups at -positions to alkoxy groups at -positions (molecule 1 vs. 2) increases 2PA cross-sections by a factor of nearly 2. This also results in the red shift of entire 1PA spectrum by 30 nm (500 cm -1). The 2PA spectrum also experiences the red shift. This shows that addition of oxygen atoms increases -conjugation.

2) Addition of extra CHO group (molecule 1 vs. 6) results in a slight decrease of 2PA cross-section as compared to better purified compound 1 and in slight increase of the cross-sections compared to 1a and 1b. The 1PA spectrum practically does not change.

3) Substituting an external benzene ring with another alkoxy group (molecule 4 vs. 6) produces a nearly symmetrical molecule. This shifts both Qx and Qy peaks closer to each other so that they overlap. A similar shift appears in 2PA

spectrum. The value of 2PA cross-section reduces by a factor of nearly 2, which is probably because of reduce of the difference in dipole moments in more symmetrical molecule.

4) Addition of extra hydrogen atoms (molecule 3 vs. 4) reduces degree of symmetry. This slightly increases the 2PA cross-section for molecule 3. However, its cross-section is smaller than for molecules 1 and 6. The reason is more symmetry and thus less difference in dipole moments in the molecule 3

5) Change of substituent from molecule 3 to 5 makes the molecule less symmetrical, and thus increase 2PA cross-section. However, molecule 6, and especially 1 have the highest 2PA cross-sections among all studied samples.

2PA-sensitive phtalocyanines: comparison for 3D memory

2

1

2 2

~ max

~ max

w

w

w r F A B

NBR

SNR

2 / 22 F A B

Molecule 1 Molecule 2 Molecule 3 Molecule 4 Molecule 5 Molecule 6

0.048 0.011 0.037 0.012 0.046 0.010

12.2 12.0 12.8* 13.1 29.4* 11.1

*For molecules 3 and 5 absorption spectra of tautomer forms T1 and T2 significantly overlaps that makes them not practical as photochromes for 3D optical memory

900 nmw r

SNR-SBR comparison

1, cm2 (, nm) 2,GM (, nm) F AB

4.810-16 (752) 816 (865) 0.32 0.0080

Summary• Because of the requirement of fast speed writing and readout, the storage materials need to have high molecular 2PA cross section, 2>103-104 GM• It is evident that the crucial points in this approach are the two-photon sensitivity of a molecule and the possibility of its photochemical transformation from one form to another• Careful choice of excitation frequency, along with suitable combination of 1PA and 2PA properties allow minimizing the negative impact of underlying near resonance hot band absorption• A brief analysis of changes in 2PA spectra and cross-sections due to different substituent groups is provided and allow to deduce structure-to-properties relations• We conclude that from the set of studied molecules compound 1 is the most promising for rewritable 3D optical memory.

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