Klaus Meerholz, Erwin Mecher, Reinhard Bittner, and Yessica De Nardin, "Competing photorefractive gratings in organic thin-film devices," J. Opt. Soc. Am. B 15, 2114-2124 (1998)
Recently, amorphous organic photorefractive materials have generated great excitement because of their excellent performance, which permits applications in high-density holographic storage, real-time image processing, and phase conjugation. However, the heterostructure of the devices (consisting of glass cover slides, transparent electrodes, and the photorefractive material) and the tilted recording and readout geometry commonly used result in multiple reflected beams in addition to the normal object and reference beams. This result leads to several photorefractive gratings competing inside the photorefractive polymer device. We prove the coexistence of these gratings by two-beam coupling and four-wave mixing experiments and demonstrate how to distinguish between them.
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Calculation of Relevant Beam Intensities for and a
Beam Intensity or Reflectivity
Polarized
Polarized
Polarized
Polarized
810
1120
1500
1500
0.85
0.66
0.98
0.95
690
740
1470
1420
0.027
0.046
0.011
0.009
15
27
13
10
140
200
130
170
0.85
0.66
0.98
0.95
120
130
130
170
0.011
0.023
0.004
0.004
1
3
0.5
0.7
0.103
0.129
–
–
13
17
–
–
Initial light intensity measured outside the device. reflectance of the air–glass–ITO–polymer interfaces calculated from Snell’s and Fresnel’s laws and the measured refractive indices. The interference of reflections 2 and 3 was taken into account. intensity of light entering the PR polymer layer calculated from and calculated reflectance of the polymer–ITO–glass interface, with the interference of reflections 4 and 5 taken into account. initial intensity of the reflected beams calculated from and Rows and are for ITO thicknesses of 150 and 80 nm, respectively, for the second contact electrode; the first contact had an ITO thickness of 150 nm in all cases [cf. Fig. 1(b)]. The bold-face numbers are those used for evaluation of the data.
Table 2
Tilt Angles Calculated from the External Angles from Snell’s Law and the Measured Refractive Index; Grating Periods Calculated from the Internal Angles; Grating Contrast Factors
a for Calculated According to Eq. (1); and Light Intensity
b for the Six Coexisting PR Gratings
c
Grating
[deg]
[μm]
[μW]
[μW]
30.2
3.42
1.00
1430
1.00
2890
3.42
0.96
42
0.99
23
90.0
0.23
0.29
705
0.9
1482
90.0
0.24
0.37
767
0.085
1452
86.6
0.235
0.38
717
0.085
1480
0.235
0.28
755
0.09
1432
29.8
3.15
1.00 (1.00)
250 (250)
1.00
300
3.15
0.92 (0.99)
4 (30)
0.98
1
90.0
0.21
0.19 (0.58)
121 (133)
0.055
131
90.0
0.22
0.27 (0.64)
133 (147)
0.055
171
86.6
0.215
0.28 (0.66)
123 (137)
0.055
131
0.215
0.18 (0.57)
131 (143)
0.055
171
Note that the contrast factors of all gratings (except for the grating) are field dependent (see, for example, Fig. 8 below).
See Table 1 for details.
All values are given for inside the material; at and at
Tables (2)
Table 1
Calculation of Relevant Beam Intensities for and a
Beam Intensity or Reflectivity
Polarized
Polarized
Polarized
Polarized
810
1120
1500
1500
0.85
0.66
0.98
0.95
690
740
1470
1420
0.027
0.046
0.011
0.009
15
27
13
10
140
200
130
170
0.85
0.66
0.98
0.95
120
130
130
170
0.011
0.023
0.004
0.004
1
3
0.5
0.7
0.103
0.129
–
–
13
17
–
–
Initial light intensity measured outside the device. reflectance of the air–glass–ITO–polymer interfaces calculated from Snell’s and Fresnel’s laws and the measured refractive indices. The interference of reflections 2 and 3 was taken into account. intensity of light entering the PR polymer layer calculated from and calculated reflectance of the polymer–ITO–glass interface, with the interference of reflections 4 and 5 taken into account. initial intensity of the reflected beams calculated from and Rows and are for ITO thicknesses of 150 and 80 nm, respectively, for the second contact electrode; the first contact had an ITO thickness of 150 nm in all cases [cf. Fig. 1(b)]. The bold-face numbers are those used for evaluation of the data.
Table 2
Tilt Angles Calculated from the External Angles from Snell’s Law and the Measured Refractive Index; Grating Periods Calculated from the Internal Angles; Grating Contrast Factors
a for Calculated According to Eq. (1); and Light Intensity
b for the Six Coexisting PR Gratings
c
Grating
[deg]
[μm]
[μW]
[μW]
30.2
3.42
1.00
1430
1.00
2890
3.42
0.96
42
0.99
23
90.0
0.23
0.29
705
0.9
1482
90.0
0.24
0.37
767
0.085
1452
86.6
0.235
0.38
717
0.085
1480
0.235
0.28
755
0.09
1432
29.8
3.15
1.00 (1.00)
250 (250)
1.00
300
3.15
0.92 (0.99)
4 (30)
0.98
1
90.0
0.21
0.19 (0.58)
121 (133)
0.055
131
90.0
0.22
0.27 (0.64)
133 (147)
0.055
171
86.6
0.215
0.28 (0.66)
123 (137)
0.055
131
0.215
0.18 (0.57)
131 (143)
0.055
171
Note that the contrast factors of all gratings (except for the grating) are field dependent (see, for example, Fig. 8 below).
See Table 1 for details.
All values are given for inside the material; at and at
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