OFFICE OF NAVAL RESEARCH GRANT: N R&T CODE: Scientific Officer: Dr. Kenneth J. Wynne TECHNICAL REPORT NO.

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1 OFFICE OF NAVAL RESEARCH GRANT: N R&T CODE: Scientific Officer: Dr. Kenneth J. Wynne TECHNICAL REPORT NO. 48 Polarization Holographic Gratings in Azopolymers for Detecting and Producing Circularly Polarized Light by P. Rochon, V. Drnoyan and A. Natansohn Submitted for publication in International Conference on Applications of Photonics Technology (SPIE) Department of Chemistry Queen's University Kingston, On., Canada June 23,1998 Reproduction in whole or in part is permitted for any purpose of the United States Government This document has been approved for public release and sale; its distribution is unlimited. 00 QUALITY D53PECTBD ? W

2 REPORT DOCUMENTATION PAGE Q.'.i= NO. 07:-!-G!33., i,r-- I:' if!»1 "» ' f.ii-l. I!i'l''''1 till " 5''.' «- 7;,..«.,««.-, *.-«.< '<>-..-*««- «" f 1^-;^:,T^;;.":v J,-;,iv J H, n. e '-^"i^i^h";^ iru^j/irivt?.-' eq ir<3 i- I"*' i- rt, ', 1 0., -., W>.'ii'.»'"".""-»* "" ""' 3 «PORT TYPE ANO DATES COVERED 1 AGENCY USE ONLY (L»v bunk> I 2. R?Oni DA. c J.., D..* /, Q A. TITLE AMD SU3TITLE 1 vju "- ~ - L-^-i S. FUNDING NUM3ERS Polarization Holographic Gratings in Azopolymers for Detecting and Producing Circularly Polarized Light 6. AUTHORS) P. Rochon, V. Drnoyan and A. Natansohn N PERFORMING ORGANIZATION NAME(S) AS>>..UORESS(ES) Department of Chemistry Queen's University Kingston, Ontario K7L 3N6 Canada 9. SPONSORING/MONITORING AGENCY NAME(S) AMU AuORESS(ES) Department of the Navy Office of the Naval Research 800 North Quincy Street, Arlington, VA SUPPLEMENTARY NOTES 8. PERFORMING ORGANLIATION REPORT HUM5ER SPONSORING/MONITORING AGENCY REPORT NU.M3ES International Conference on Applications of Photonics Technology (SPIE) 12a DISTRIBUTION/AVAILABILITY STATEMENT Reproduction in whole or in part is permitted for any purpose of the United States Government. This document has been approved for public release and sale; its distribution is unlimited. 13. A3STRACT {Maximum 20Ovtoixb) 12b. DISTRIBUTION CODE Polarization holographic gratings were inscribed in azobenzene side chain polymer films. The polarization gratings were produced using two orthogonally circularly polarized beams and the resulting stable transmission gratings were studied using a low power HeNe laser The gratings were observed to efficiently separate left and right circularly polarized light from the probe beam and two generate to elliptically polarized beams in the first order diffraction direction. Azobenzene polymers, holographic gratings, device, circularly, polarized light, separator 17. SECURITY CLASSIFICATION OF REPORT unclassified N5.N SECURITY CLASSIFICATION OF THIS PAGE unclassified 13. SECURITY CLASSIFICATION OF ABSTRACT ini-1 a^i f 1P f 15. NUMSER OF PAGES 16. PRJCE COD: 20.'LIMITATION OF A35T?J unlimited S: a.-.a3:d Fo^TiiT^- ^

3 Polarization holographic graüngs in azopolymers for detecting and producing circularly polarized light. P. Rochon Department of Physics, Royal Military College of Canada. Kingston. Ontario K7K 7B4 V. Dmoyan and A. Natansolin Department of Chemistry. Queen's University Kingston Ontario K7L 3N6 ABSTRACT Polarization holographic gratings were inscribed in azobenzene side chain polymer Films. The polarization»ratings were produced usine two orthogonally circularly polarized beams and the resulting stable transmission gratings were studied using a low power HcNe laser. The gratinss were observed to efficiently separate left and right circularly polarized light from the probe beam and two generate two elliptically polarized beams in the first order diffraction direction. 2. INTRODUCTION The availability of materials in which optical arusotropv can be photoinduced has led to a number of interesting ctudies on die recording of polarization holograms 1?. These are made by the interference of two beams recorded in die mnenal where die interference pattern is not a variation of intensity but rather a variation in the polarization state of the resultant wave in die material. The local polarization of die light is then recorded in an optically anisotropic material. In the present paper we consider the case when the holographic recording beams are of equal intensity and are orthogonally circularly polarized. One of die interesting properties of the holographic grating produced by these two beams is that it diffracts'die left () and right-hand () circularly polarized light from a probe beam into two separate directions. Tliis can dien lead to a simple device that could measure the total polarization state of an input beam over a wide u-nelenodi ran*e The dieorv also predict that this craung could be used to produce circularly polarized light of selected handedness again over a wide wave lengdi range. In the present study we consider the production of these holographic «ratings in azobenzene side chain polymers Azobenzene side chain polymers have been shown to have large, stable birefringence can be optically induced usin«moderate power argon lasers and short exposure times* The recording medium is a thin film ( ca. 400 nm duck) which is made bv spin coating the polvmer which is dissolved in tetrahydrofuran onto a glass substrate. The azobenzene molecules are intrinsically anisotropic but thev are initially deposited in random directions making die film amorphous and Isotropie The molecules can be made to change shape and direction by the process of photoisomenzation. Upon exposure to lmearlv polarized light the molecules tend to re-align in a direction that is perpendicular to the polarization direction. This results in a local optical arusotropv that can be detected using a probe which does not cause photoisomenzation but which is still sensitive to die local birefringence. The optically induced birefringence in side chain azopolymers is stable over extended periods ( years). therefore die holographic graüngs can be components of a polarization measurement system as long as the films are protected against erasure.

4 3.EXPERIMENT The holographic polarization grating was produced by the superposition of two orthogonal circularly polarized beams as illustrated below: probe So film FIGURE 1: Optical set-up S + i The wrilin«beams 1 and 2. are from a 50 inw/cnr Argon laser at 488 nm and the probe beam is trom a 10 pw HeNe laser at 63? S ran. The film was a s.de chain azopolymer*. pdrlm. which was cast onto a glass substrate. The writing beams are orthogonally circularly polarized to produce the following polarization patterns on the film Aj^,^i nr ^.«?.?! A 12T '/- \i/ ****&$ 1- /N ILa ^ = - A ^ is ^-^ & ^5^, FIGURE 2 : Polarization gratings We note that Ute first pattern is a rotation of the first pattern about the x-axis or z-axis( out of the paper).the anale between the writuw beams was adjusted to give a grating spacing of about 6 micrometers. The polarization graues wet produced bv ing for 100 seconds, whichls enough time for the optically induced birefringence to reach saturation l^t^l birefringence was Uten allowed to relax in die da* for 500 seconds to reach the more ^^^te birefringence levels of An= The probe beam was then used to obtain the diffraction characteristics of the gratings_ The prob^beam portion state was varied using a quarter wave plate and die polarization could be continuously varied from left circular to linear to right circular.

5 4. RESULTS AND DISCUSSION The polarization grating can be described by the following transmission Jone 's matrix JÖ ( (\ 0\ i 1 T = e 1% WAq)) 0 1 J ^2 V J 1 -i \ -10 / +sin(z^p? / V" -n Where A, IS the average phase delay through the film. Aa> = "d-an/a. is die anisotropic phase delay due to the birefringence. and 6 = 2-x/A is the phase delav along die grating with spacing A. In the above equation trie first term in die brackets is the dircctlv transmitted beam, the second term is the beam in die +1 order of diffraction and the third term is the beam in die -1 order of diffraction. One can readily sec that in die above case a right circularly polarised beam of light. would only L- be diffracted into die -1 order and that die resultant beam would be left circularly polarised. We have investigated dus anisotropic diffraction property of the polarization gratings for circularly polarized light and die results are summarised in the following table which gives the direction and polarization state of the diffracted beams. TABLE1: Diffraction of a circularly polarized probe beam BEAM 1 Probe S-, S.i The results are in agreement with die above theoretical predictions. For example when Beam 1 of the writing beam is and the probe beam Is dien we observe that the diffracted beam occurs mostly in die -1 direction and die is it polarized. The beam in the +1 direction is less dian 2% ofthat in the -1 direction. When the probe beam is dien the light is diffracted into the +1 direction and is. Also as indicated in die table, when the writing geometry or the sample geometry are inverted then the diffraction of the polarized beams is also affected.

6 i >u<* rak» t^m Hop«: not over write the inscribed information. The The holographic grating is stable as ^"^.^.^"^^rjln In figure 3 we present the results linearly polarized test beam was constant and rotating a quarter-wave plate vancd the polanzauon state content (%) 80 FIGURE 3: Polarizauon detection of a lest beam TV res u, K,nd,ea,ed Ü«d,e polar.zado of,.,c,cs, *;- ^ "^'^ e^ed^l 1,» u S ed in device applications. However, d,e ddffracuon efficiency ; was,,oun^*» ".^ du Uie Mabi'iiv nf the holographic srating can also b^ inu-casca D\ UMIU IU 0 I«- 0 those chromophores during die process of photoinduced birefnngence. 5. ACKNOWLEDGEMENTS Funding was provided by the Office of Naval Research USA. NSERC Canada, and the Department of National Defence of Canada. 6. REFERENCES 1- Sh.D.KakicliashviliOpt.Spectrosc. (1977).42. p ,,,,, i T Todorov L Nikolova. and N. Tomova Appl. Optics (1984). 2.K 4^0 ;-4., 1 _ I" Ü-S^r^^taTIÄiS^ Ä" Mode Op,,c, O^,»..»-I» 7- F. Lagngne-Laberüiet. T. Buffeteau and C. Sounsseau. J. Phys. Chem. (1998). B M ibw.