Abstract

Using a two-laser static tester, we measured the crystallization temperature and the thermal conductivity of a phase-change alloy thin film used in write-once–read-many media of optical data storage. The experimental technique, in general, and the calibration procedures, in particular, are described. The measurement results are used as entry points into numerical calculations that ultimately yield estimates of the material parameters. Valuable information about the dynamics of mark formation (i.e., localized crystallization) in amorphous phase-change alloy films is obtained from the observed variations of the sample reflectance under short-pulse and long-pulse recording conditions. The dependence of these reflectance variations on the laser pulse power has also been investigated.

© 2002 Optical Society of America

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  1. J. Feinleib, “Rapid reversible light-induced crystallization of an amorphous semiconductor,” Appl. Phys. Lett. 18, 254–257 (1971).
    [CrossRef]
  2. R. J. von Gutfeld, P. Chaudhari, “Laser writing and erasing on chalcogenide films,” J. Appl. Phys. 43, 4688–4693 (1972).
    [CrossRef]
  3. M. Takenaga, N. Yamada, S. Ohara, K. Nishiuchi, M. Nagashima, T. Kashihara, S. Nakamura, T. Yamashita, “New optical erasable medium using tellurium suboxide thin film,” in Optical Storage Media, A. E. Bell, A. A. Jamberdino, eds., Proc. SPIE420, 173–177 (1983).
    [CrossRef]
  4. M. Terao, T. Nishida, Y. Miyauchi, S. Horigome, T. Kaku, N. Ohta, “In-Se based phase-change reversible optical recording film,” in Optical Mass Data Storage II, R. P. Freese, A. A. Jamberdino, M. R. de Haan, eds., Proc. SPIE695, 105–109 (1986).
    [CrossRef]
  5. T. Ohta, M. Uchida, K. Yoshioka, K. Inoue, T. Akiyama, S. Furukawa, K. Kotera, S. Nakamura, “Million cycle overwritable phase-change optical disk media,” in Optical Data Storage Topical Meeting, G. R. Knight, C. N. Kurtz, eds., Proc. SPIE1078, 27–34 (1989).
    [CrossRef]
  6. C. D. Eden, “Vanadium dioxide storage material,” Opt. Eng. 20, 377–378 (1981).
    [CrossRef]
  7. N. Akahira, T. Ohta, N. Yamada, M. Takenaga, T. Yamashita, “Sub-oxide thin films for an optical recording disk,” in Optical Disk Technology, R. A. Sprague, ed., Proc. SPIE329, 195–201 (1982).
    [CrossRef]
  8. M. Chen, V. Marrello, “Pulse width transfer function of tellurium-alloy disks,” in Optical Storage Media, A. E. Bell, A. A. Jamberdino, eds., Proc. SPIE420, 255–259 (1983).
    [CrossRef]
  9. W.-Y. Lee, “Thin Te and Te alloy films for optical data storage,” in Optical Storage Media, A. E. Bell, A. A. Jamberdino, eds., Proc. SPIE420, 265–272 (1983).
    [CrossRef]
  10. T. Ohta, K. Kotera, K. Kimura, N. Akahira, M. Takenaga, “New write-once media based on Te-TeO2 for optical disks,” in Optical Mass Data Storage II, R. P. Freese, A. A. Jamberdino, M. R. de Haan, eds., Proc. SPIE695, 2–9 (1986).
    [CrossRef]
  11. N. Yamada, M. Takao, M. Takenaga, “Te-Ge-Sn-Au phase-change recording film for optical disk,” in Optical Mass Data Storage II, R. P. Freese, A. A. Jamberdino, M. R. de Haan, eds., Proc. SPIE695, 79–85 (1986).
    [CrossRef]
  12. Y.-C. Hsieh, M. Mansuripur, J. Volkmer, A. Brewen, “Measurement of the thermal coefficients of nonreversible phase-change optical recording films,” Appl. Opt. 36, 866–872 (1997).
    [CrossRef] [PubMed]
  13. M. Mansuripur, J. K. Erwin, W. Bletscher, P. K. Khulbe, K. Sadeghi, X. Xun, A. Gupta, S. B. Mendes, “Static tester for characterization of phase-change, dye polymer, and magneto-optical media for optical data storage,” Appl. Opt. 38, 7095–7104 (1999).
    [CrossRef]
  14. C. Peng, M. Mansuripur, “Measurement of the thermal conductivity of erasable phase-change optical recording media,” Appl. Opt. 39, 2347–2352 (2000).
    [CrossRef]
  15. TEMPROFILE is a product of MM Research, Inc., Tucson, Arizona. The theoretical basis of the program is described in M. Mansuripur, G. A. N. Connell, J. W. Goodman, “Laser-induced local heating of multilayers,” Appl. Opt. 21, 1106–1114 (1982).
  16. P. K. Khulbe, T. Hurst, M. Mansuripur, “Temperature-dependence of optical constants in phase-change media,” in Optical Data Storage 2001, T. Hurst, S. Kobayashi, eds., Proc. SPIE4342, 121–123 (2002).
    [CrossRef]

2000 (1)

1999 (1)

1997 (1)

1981 (1)

C. D. Eden, “Vanadium dioxide storage material,” Opt. Eng. 20, 377–378 (1981).
[CrossRef]

1972 (1)

R. J. von Gutfeld, P. Chaudhari, “Laser writing and erasing on chalcogenide films,” J. Appl. Phys. 43, 4688–4693 (1972).
[CrossRef]

1971 (1)

J. Feinleib, “Rapid reversible light-induced crystallization of an amorphous semiconductor,” Appl. Phys. Lett. 18, 254–257 (1971).
[CrossRef]

Akahira, N.

T. Ohta, K. Kotera, K. Kimura, N. Akahira, M. Takenaga, “New write-once media based on Te-TeO2 for optical disks,” in Optical Mass Data Storage II, R. P. Freese, A. A. Jamberdino, M. R. de Haan, eds., Proc. SPIE695, 2–9 (1986).
[CrossRef]

N. Akahira, T. Ohta, N. Yamada, M. Takenaga, T. Yamashita, “Sub-oxide thin films for an optical recording disk,” in Optical Disk Technology, R. A. Sprague, ed., Proc. SPIE329, 195–201 (1982).
[CrossRef]

Akiyama, T.

T. Ohta, M. Uchida, K. Yoshioka, K. Inoue, T. Akiyama, S. Furukawa, K. Kotera, S. Nakamura, “Million cycle overwritable phase-change optical disk media,” in Optical Data Storage Topical Meeting, G. R. Knight, C. N. Kurtz, eds., Proc. SPIE1078, 27–34 (1989).
[CrossRef]

Bletscher, W.

Brewen, A.

Chaudhari, P.

R. J. von Gutfeld, P. Chaudhari, “Laser writing and erasing on chalcogenide films,” J. Appl. Phys. 43, 4688–4693 (1972).
[CrossRef]

Chen, M.

M. Chen, V. Marrello, “Pulse width transfer function of tellurium-alloy disks,” in Optical Storage Media, A. E. Bell, A. A. Jamberdino, eds., Proc. SPIE420, 255–259 (1983).
[CrossRef]

Eden, C. D.

C. D. Eden, “Vanadium dioxide storage material,” Opt. Eng. 20, 377–378 (1981).
[CrossRef]

Erwin, J. K.

Feinleib, J.

J. Feinleib, “Rapid reversible light-induced crystallization of an amorphous semiconductor,” Appl. Phys. Lett. 18, 254–257 (1971).
[CrossRef]

Furukawa, S.

T. Ohta, M. Uchida, K. Yoshioka, K. Inoue, T. Akiyama, S. Furukawa, K. Kotera, S. Nakamura, “Million cycle overwritable phase-change optical disk media,” in Optical Data Storage Topical Meeting, G. R. Knight, C. N. Kurtz, eds., Proc. SPIE1078, 27–34 (1989).
[CrossRef]

Gupta, A.

Horigome, S.

M. Terao, T. Nishida, Y. Miyauchi, S. Horigome, T. Kaku, N. Ohta, “In-Se based phase-change reversible optical recording film,” in Optical Mass Data Storage II, R. P. Freese, A. A. Jamberdino, M. R. de Haan, eds., Proc. SPIE695, 105–109 (1986).
[CrossRef]

Hsieh, Y.-C.

Hurst, T.

P. K. Khulbe, T. Hurst, M. Mansuripur, “Temperature-dependence of optical constants in phase-change media,” in Optical Data Storage 2001, T. Hurst, S. Kobayashi, eds., Proc. SPIE4342, 121–123 (2002).
[CrossRef]

Inoue, K.

T. Ohta, M. Uchida, K. Yoshioka, K. Inoue, T. Akiyama, S. Furukawa, K. Kotera, S. Nakamura, “Million cycle overwritable phase-change optical disk media,” in Optical Data Storage Topical Meeting, G. R. Knight, C. N. Kurtz, eds., Proc. SPIE1078, 27–34 (1989).
[CrossRef]

Kaku, T.

M. Terao, T. Nishida, Y. Miyauchi, S. Horigome, T. Kaku, N. Ohta, “In-Se based phase-change reversible optical recording film,” in Optical Mass Data Storage II, R. P. Freese, A. A. Jamberdino, M. R. de Haan, eds., Proc. SPIE695, 105–109 (1986).
[CrossRef]

Kashihara, T.

M. Takenaga, N. Yamada, S. Ohara, K. Nishiuchi, M. Nagashima, T. Kashihara, S. Nakamura, T. Yamashita, “New optical erasable medium using tellurium suboxide thin film,” in Optical Storage Media, A. E. Bell, A. A. Jamberdino, eds., Proc. SPIE420, 173–177 (1983).
[CrossRef]

Khulbe, P. K.

M. Mansuripur, J. K. Erwin, W. Bletscher, P. K. Khulbe, K. Sadeghi, X. Xun, A. Gupta, S. B. Mendes, “Static tester for characterization of phase-change, dye polymer, and magneto-optical media for optical data storage,” Appl. Opt. 38, 7095–7104 (1999).
[CrossRef]

P. K. Khulbe, T. Hurst, M. Mansuripur, “Temperature-dependence of optical constants in phase-change media,” in Optical Data Storage 2001, T. Hurst, S. Kobayashi, eds., Proc. SPIE4342, 121–123 (2002).
[CrossRef]

Kimura, K.

T. Ohta, K. Kotera, K. Kimura, N. Akahira, M. Takenaga, “New write-once media based on Te-TeO2 for optical disks,” in Optical Mass Data Storage II, R. P. Freese, A. A. Jamberdino, M. R. de Haan, eds., Proc. SPIE695, 2–9 (1986).
[CrossRef]

Kotera, K.

T. Ohta, K. Kotera, K. Kimura, N. Akahira, M. Takenaga, “New write-once media based on Te-TeO2 for optical disks,” in Optical Mass Data Storage II, R. P. Freese, A. A. Jamberdino, M. R. de Haan, eds., Proc. SPIE695, 2–9 (1986).
[CrossRef]

T. Ohta, M. Uchida, K. Yoshioka, K. Inoue, T. Akiyama, S. Furukawa, K. Kotera, S. Nakamura, “Million cycle overwritable phase-change optical disk media,” in Optical Data Storage Topical Meeting, G. R. Knight, C. N. Kurtz, eds., Proc. SPIE1078, 27–34 (1989).
[CrossRef]

Lee, W.-Y.

W.-Y. Lee, “Thin Te and Te alloy films for optical data storage,” in Optical Storage Media, A. E. Bell, A. A. Jamberdino, eds., Proc. SPIE420, 265–272 (1983).
[CrossRef]

Mansuripur, M.

Marrello, V.

M. Chen, V. Marrello, “Pulse width transfer function of tellurium-alloy disks,” in Optical Storage Media, A. E. Bell, A. A. Jamberdino, eds., Proc. SPIE420, 255–259 (1983).
[CrossRef]

Mendes, S. B.

Miyauchi, Y.

M. Terao, T. Nishida, Y. Miyauchi, S. Horigome, T. Kaku, N. Ohta, “In-Se based phase-change reversible optical recording film,” in Optical Mass Data Storage II, R. P. Freese, A. A. Jamberdino, M. R. de Haan, eds., Proc. SPIE695, 105–109 (1986).
[CrossRef]

Nagashima, M.

M. Takenaga, N. Yamada, S. Ohara, K. Nishiuchi, M. Nagashima, T. Kashihara, S. Nakamura, T. Yamashita, “New optical erasable medium using tellurium suboxide thin film,” in Optical Storage Media, A. E. Bell, A. A. Jamberdino, eds., Proc. SPIE420, 173–177 (1983).
[CrossRef]

Nakamura, S.

M. Takenaga, N. Yamada, S. Ohara, K. Nishiuchi, M. Nagashima, T. Kashihara, S. Nakamura, T. Yamashita, “New optical erasable medium using tellurium suboxide thin film,” in Optical Storage Media, A. E. Bell, A. A. Jamberdino, eds., Proc. SPIE420, 173–177 (1983).
[CrossRef]

T. Ohta, M. Uchida, K. Yoshioka, K. Inoue, T. Akiyama, S. Furukawa, K. Kotera, S. Nakamura, “Million cycle overwritable phase-change optical disk media,” in Optical Data Storage Topical Meeting, G. R. Knight, C. N. Kurtz, eds., Proc. SPIE1078, 27–34 (1989).
[CrossRef]

Nishida, T.

M. Terao, T. Nishida, Y. Miyauchi, S. Horigome, T. Kaku, N. Ohta, “In-Se based phase-change reversible optical recording film,” in Optical Mass Data Storage II, R. P. Freese, A. A. Jamberdino, M. R. de Haan, eds., Proc. SPIE695, 105–109 (1986).
[CrossRef]

Nishiuchi, K.

M. Takenaga, N. Yamada, S. Ohara, K. Nishiuchi, M. Nagashima, T. Kashihara, S. Nakamura, T. Yamashita, “New optical erasable medium using tellurium suboxide thin film,” in Optical Storage Media, A. E. Bell, A. A. Jamberdino, eds., Proc. SPIE420, 173–177 (1983).
[CrossRef]

Ohara, S.

M. Takenaga, N. Yamada, S. Ohara, K. Nishiuchi, M. Nagashima, T. Kashihara, S. Nakamura, T. Yamashita, “New optical erasable medium using tellurium suboxide thin film,” in Optical Storage Media, A. E. Bell, A. A. Jamberdino, eds., Proc. SPIE420, 173–177 (1983).
[CrossRef]

Ohta, N.

M. Terao, T. Nishida, Y. Miyauchi, S. Horigome, T. Kaku, N. Ohta, “In-Se based phase-change reversible optical recording film,” in Optical Mass Data Storage II, R. P. Freese, A. A. Jamberdino, M. R. de Haan, eds., Proc. SPIE695, 105–109 (1986).
[CrossRef]

Ohta, T.

T. Ohta, M. Uchida, K. Yoshioka, K. Inoue, T. Akiyama, S. Furukawa, K. Kotera, S. Nakamura, “Million cycle overwritable phase-change optical disk media,” in Optical Data Storage Topical Meeting, G. R. Knight, C. N. Kurtz, eds., Proc. SPIE1078, 27–34 (1989).
[CrossRef]

N. Akahira, T. Ohta, N. Yamada, M. Takenaga, T. Yamashita, “Sub-oxide thin films for an optical recording disk,” in Optical Disk Technology, R. A. Sprague, ed., Proc. SPIE329, 195–201 (1982).
[CrossRef]

T. Ohta, K. Kotera, K. Kimura, N. Akahira, M. Takenaga, “New write-once media based on Te-TeO2 for optical disks,” in Optical Mass Data Storage II, R. P. Freese, A. A. Jamberdino, M. R. de Haan, eds., Proc. SPIE695, 2–9 (1986).
[CrossRef]

Peng, C.

Sadeghi, K.

Takao, M.

N. Yamada, M. Takao, M. Takenaga, “Te-Ge-Sn-Au phase-change recording film for optical disk,” in Optical Mass Data Storage II, R. P. Freese, A. A. Jamberdino, M. R. de Haan, eds., Proc. SPIE695, 79–85 (1986).
[CrossRef]

Takenaga, M.

N. Yamada, M. Takao, M. Takenaga, “Te-Ge-Sn-Au phase-change recording film for optical disk,” in Optical Mass Data Storage II, R. P. Freese, A. A. Jamberdino, M. R. de Haan, eds., Proc. SPIE695, 79–85 (1986).
[CrossRef]

N. Akahira, T. Ohta, N. Yamada, M. Takenaga, T. Yamashita, “Sub-oxide thin films for an optical recording disk,” in Optical Disk Technology, R. A. Sprague, ed., Proc. SPIE329, 195–201 (1982).
[CrossRef]

M. Takenaga, N. Yamada, S. Ohara, K. Nishiuchi, M. Nagashima, T. Kashihara, S. Nakamura, T. Yamashita, “New optical erasable medium using tellurium suboxide thin film,” in Optical Storage Media, A. E. Bell, A. A. Jamberdino, eds., Proc. SPIE420, 173–177 (1983).
[CrossRef]

T. Ohta, K. Kotera, K. Kimura, N. Akahira, M. Takenaga, “New write-once media based on Te-TeO2 for optical disks,” in Optical Mass Data Storage II, R. P. Freese, A. A. Jamberdino, M. R. de Haan, eds., Proc. SPIE695, 2–9 (1986).
[CrossRef]

Terao, M.

M. Terao, T. Nishida, Y. Miyauchi, S. Horigome, T. Kaku, N. Ohta, “In-Se based phase-change reversible optical recording film,” in Optical Mass Data Storage II, R. P. Freese, A. A. Jamberdino, M. R. de Haan, eds., Proc. SPIE695, 105–109 (1986).
[CrossRef]

Uchida, M.

T. Ohta, M. Uchida, K. Yoshioka, K. Inoue, T. Akiyama, S. Furukawa, K. Kotera, S. Nakamura, “Million cycle overwritable phase-change optical disk media,” in Optical Data Storage Topical Meeting, G. R. Knight, C. N. Kurtz, eds., Proc. SPIE1078, 27–34 (1989).
[CrossRef]

Volkmer, J.

von Gutfeld, R. J.

R. J. von Gutfeld, P. Chaudhari, “Laser writing and erasing on chalcogenide films,” J. Appl. Phys. 43, 4688–4693 (1972).
[CrossRef]

Xun, X.

Yamada, N.

M. Takenaga, N. Yamada, S. Ohara, K. Nishiuchi, M. Nagashima, T. Kashihara, S. Nakamura, T. Yamashita, “New optical erasable medium using tellurium suboxide thin film,” in Optical Storage Media, A. E. Bell, A. A. Jamberdino, eds., Proc. SPIE420, 173–177 (1983).
[CrossRef]

N. Akahira, T. Ohta, N. Yamada, M. Takenaga, T. Yamashita, “Sub-oxide thin films for an optical recording disk,” in Optical Disk Technology, R. A. Sprague, ed., Proc. SPIE329, 195–201 (1982).
[CrossRef]

N. Yamada, M. Takao, M. Takenaga, “Te-Ge-Sn-Au phase-change recording film for optical disk,” in Optical Mass Data Storage II, R. P. Freese, A. A. Jamberdino, M. R. de Haan, eds., Proc. SPIE695, 79–85 (1986).
[CrossRef]

Yamashita, T.

N. Akahira, T. Ohta, N. Yamada, M. Takenaga, T. Yamashita, “Sub-oxide thin films for an optical recording disk,” in Optical Disk Technology, R. A. Sprague, ed., Proc. SPIE329, 195–201 (1982).
[CrossRef]

M. Takenaga, N. Yamada, S. Ohara, K. Nishiuchi, M. Nagashima, T. Kashihara, S. Nakamura, T. Yamashita, “New optical erasable medium using tellurium suboxide thin film,” in Optical Storage Media, A. E. Bell, A. A. Jamberdino, eds., Proc. SPIE420, 173–177 (1983).
[CrossRef]

Yoshioka, K.

T. Ohta, M. Uchida, K. Yoshioka, K. Inoue, T. Akiyama, S. Furukawa, K. Kotera, S. Nakamura, “Million cycle overwritable phase-change optical disk media,” in Optical Data Storage Topical Meeting, G. R. Knight, C. N. Kurtz, eds., Proc. SPIE1078, 27–34 (1989).
[CrossRef]

Appl. Opt. (3)

Appl. Phys. Lett. (1)

J. Feinleib, “Rapid reversible light-induced crystallization of an amorphous semiconductor,” Appl. Phys. Lett. 18, 254–257 (1971).
[CrossRef]

J. Appl. Phys. (1)

R. J. von Gutfeld, P. Chaudhari, “Laser writing and erasing on chalcogenide films,” J. Appl. Phys. 43, 4688–4693 (1972).
[CrossRef]

Opt. Eng. (1)

C. D. Eden, “Vanadium dioxide storage material,” Opt. Eng. 20, 377–378 (1981).
[CrossRef]

Other (10)

N. Akahira, T. Ohta, N. Yamada, M. Takenaga, T. Yamashita, “Sub-oxide thin films for an optical recording disk,” in Optical Disk Technology, R. A. Sprague, ed., Proc. SPIE329, 195–201 (1982).
[CrossRef]

M. Chen, V. Marrello, “Pulse width transfer function of tellurium-alloy disks,” in Optical Storage Media, A. E. Bell, A. A. Jamberdino, eds., Proc. SPIE420, 255–259 (1983).
[CrossRef]

W.-Y. Lee, “Thin Te and Te alloy films for optical data storage,” in Optical Storage Media, A. E. Bell, A. A. Jamberdino, eds., Proc. SPIE420, 265–272 (1983).
[CrossRef]

T. Ohta, K. Kotera, K. Kimura, N. Akahira, M. Takenaga, “New write-once media based on Te-TeO2 for optical disks,” in Optical Mass Data Storage II, R. P. Freese, A. A. Jamberdino, M. R. de Haan, eds., Proc. SPIE695, 2–9 (1986).
[CrossRef]

N. Yamada, M. Takao, M. Takenaga, “Te-Ge-Sn-Au phase-change recording film for optical disk,” in Optical Mass Data Storage II, R. P. Freese, A. A. Jamberdino, M. R. de Haan, eds., Proc. SPIE695, 79–85 (1986).
[CrossRef]

TEMPROFILE is a product of MM Research, Inc., Tucson, Arizona. The theoretical basis of the program is described in M. Mansuripur, G. A. N. Connell, J. W. Goodman, “Laser-induced local heating of multilayers,” Appl. Opt. 21, 1106–1114 (1982).

P. K. Khulbe, T. Hurst, M. Mansuripur, “Temperature-dependence of optical constants in phase-change media,” in Optical Data Storage 2001, T. Hurst, S. Kobayashi, eds., Proc. SPIE4342, 121–123 (2002).
[CrossRef]

M. Takenaga, N. Yamada, S. Ohara, K. Nishiuchi, M. Nagashima, T. Kashihara, S. Nakamura, T. Yamashita, “New optical erasable medium using tellurium suboxide thin film,” in Optical Storage Media, A. E. Bell, A. A. Jamberdino, eds., Proc. SPIE420, 173–177 (1983).
[CrossRef]

M. Terao, T. Nishida, Y. Miyauchi, S. Horigome, T. Kaku, N. Ohta, “In-Se based phase-change reversible optical recording film,” in Optical Mass Data Storage II, R. P. Freese, A. A. Jamberdino, M. R. de Haan, eds., Proc. SPIE695, 105–109 (1986).
[CrossRef]

T. Ohta, M. Uchida, K. Yoshioka, K. Inoue, T. Akiyama, S. Furukawa, K. Kotera, S. Nakamura, “Million cycle overwritable phase-change optical disk media,” in Optical Data Storage Topical Meeting, G. R. Knight, C. N. Kurtz, eds., Proc. SPIE1078, 27–34 (1989).
[CrossRef]

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Figures (17)

Fig. 1
Fig. 1

Diagram of the static tester built around a commercial polarized light microscope. The main column of the microscope, depicted on the right-hand side, contains a white-light source, polarizer and analyzer, a CCD camera, and an objective lens. The sample sits atop a computer-controlled xy translation stage. (An electromagnet is positioned below the stage for the measurement of MO samples.) The boxed elements include two laser diodes and the necessary optics for guiding the laser beams to the sample and back to the detectors.

Fig. 2
Fig. 2

Readout signal (from Laser 1) as a function of the cw power of Laser 2 taken from sample S3 at T amb = 23 °C. We obtained the various curves at different vertical positions of the sample by stepping the stage through the focal plane in Δz = 200 nm steps. The minimum required cw power P th at the onset of crystallization (i.e., at the knee of the curve) presumably occurs when the sample is at best focus. The threshold set power in this example was found to be P th = 0.188 mW.

Fig. 3
Fig. 3

Measured values of the threshold power P th at the onset of crystallization (i.e., mark formation) in the cw mode versus the sample’s ambient temperature. The objective’s NA was 0.6 in all cases. The horizontal axis intercept of the linear fit to each set of data points yields the (slow) crystallization temperature T c for each sample; the vertical axis intercept should be the value of P th at T amb = 0 °C (see Table 1).

Fig. 4
Fig. 4

Read detector’s difference signal (before and after the pulse) as a function of the set pulse power for a τ = 600 ns pulse of Laser 2 applied to sample S1. The five measurement sets were taken at vertical positions of the sample differing by Δz = 400 nm. In all cases the 0.6-NA objective was used to focus the laser beams on the sample. The threshold set power, which occurs somewhere between z 1 + 800 nm and z 1 + 1200 nm, is ∼0.406 mW.

Fig. 5
Fig. 5

Measured threshold power P th versus pulse width τ at the onset of mark formation in sample S1 in the pulsed mode of Laser 2 through a 0.6-NA objective lens. For very long pulses, P th should approach the cw threshold power of 0.188 mW.

Fig. 6
Fig. 6

Computed plots of the peak temperature within sample S1 (i.e., temperature at the center of the focused Gaussian beam at the top of the PC layer) for three assumed values of the PC layer’s specific heat, namely, C = 1.00, 1.25, 1.50 J/cm3/°C. The horizontal axis represents pulse duration τ. The Laser 2 pulse powers used in these calculations were the experimentally obtained threshold powers P th for each pulse width (see Fig. 5). The assumed diameter of the focused spot corresponded to that measured for the Laser 2 beam through our 0.6-NA objective. Note that for long pulses the peak temperature is independent of the assumed value of specific heat C.

Fig. 7
Fig. 7

Measured plots of the Laser 2 pulse shape (τ = 1.0 µs) and the corresponding reflectance variations of sample S1 versus time. Also shown are the computed plots of temperature versus time at the center of the focused spot at the sample surface. The calibrated pulse power at sample P 2 is 0.269 mW. The scattered dots represent the noisy readout signal obtained directly from the static tester’s photodetector, whereas the thick solid curve represents the smoothed-out average of these data points. The write pulse is also monitored during these measurements, and its profile in arbitrary units is superimposed as a thin-line curve on the plot of the reflectance signal. The increase in the reflectance signal at t = 0.8 µs represents the onset of crystallization. The temperature profiles (scale on the right-hand side) are computed for the specific heat values of C = 1.00 (dashed curve), C = 1.25 (dotted curve), and C = 1.50 J/cm3/°C (dash–dot curve).

Fig. 8
Fig. 8

Measured and computed plots such as in Fig. 7 for P 2 = 0.524 mW. The onset of crystallization occurs at t = 0.4 µs, corresponding to 330 °C.

Fig. 9
Fig. 9

Measured and computed plots such as in Fig. 7 for P 2 = 1.12 mW. The onset of crystallization occurs at t = 0.2 µs. At t = 0.7 µs a local maximum in the reflectance is reached, corresponding to a temperature of 470 °C. The following drop in the reflectance is interpreted as the melt onset of the material.

Fig. 10
Fig. 10

Measured and computed plots such as in Fig. 7 for P 2 = 2.36 mW. The onset of crystallization occurs at t = 0.05 µs. At t = 0.2 µs a local maximum in the reflectance is reached. The simulated temperatures above ∼600 °C are an artifact, since the simulation program does not take melting into account.

Fig. 11
Fig. 11

Measured and computed plots such as in Fig. 7 for P 2 = 4.15 mW. The onset of crystallization is below the resolution of the apparatus (<0.02 µs). At t = 0.15 µs a local maximum in the reflectance is observed, indicating the melt onset of the material. At t = 1.0 µs the reflectance almost reaches the amorphous value. Thus the molten region fills most of the read spot at the sample. The simulated temperatures above ∼600 °C are an artifact, since the simulation program does not take melting into account.

Fig. 12
Fig. 12

Sketch of the crystallization dynamics typical for large write powers. At top are the write pulse (thin curve), the reflectance curve (thick curve), and the temperature dependence (dashed curve). The bottom part shows amorphous, crystalline, and molten regions for various times during and after the write pulse (for details see text).

Fig. 13
Fig. 13

Measured reflectance signal from a cleaved silicon edge as a function of the position of a focused laser beam along a straight line perpendicular to the edge. The data points (circles) represent the sum of the signals from two detectors that observe different components of polarization of the reflected light. The best fit of an error function (i.e., indefinite integral of a Gaussian) to the sum signal yields a 1/e intensity radius of 532 nm for the focused spot along the scanned x direction. Applying the calibration factor for the translation stage yields r x = 511 nm as the 1/e intensity radius in the x direction.

Fig. 14
Fig. 14

Direct measurement of the pulse shape for τ = 10-, 15-, 20-, 30-, 40-, 50-, 60-, 80-, 100-ns pulses by use of a 0.3-ns detector and a 2-gigasample/s storage oscilloscope. The 10–90% rise and fall times are ∼3 ns in every case. The pulses overshoot by ∼30% of the nominal power, followed by a 10% undershoot, before stabilizing at the nominal power after ∼30 ns.

Fig. 15
Fig. 15

Calibration curves for the output optical power of Laser 2 (λ = 680 nm) operating in cw mode for objectives having NAs of 0.6, 0.7, 0.75, 0.8, and 1.25. Within the bounds of measurement error, the actual power (monitored at the sample) and the set power (at the laser driver) are linearly related. The best linear fits to the data points are listed in Table 2.

Fig. 16
Fig. 16

Calibration curve for Laser 2 in the pulsed mode, focused on the sample through our 0.6-NA objective lens. The plot shows the actual pulse power (monitored at the sample) versus the set power (at the laser driver). The actual power is twice the measured power (to account for the 50% duty cycle of the pulse sequence), minus the idle cw power (i.e., the power of the laser beam before being switched on). A fourth-order polynomial provides the lowest-order fit to the data points with sufficient accuracy.

Fig. 17
Fig. 17

Ratio of the average single-pulse power to the average calibration-pulse power as a function of the set power (at the laser driver). Evidently, the power of the single-pulse at the sample must be corrected, especially when the power at the sample is below 5 mW. The exponential best fit to the data points serves as a power calibration curve to correct for this nonlinear relationship.

Tables (2)

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Table 1 Extrapolated Threshold Power P th at T amb = 0 °C and Crystallization Temperature T c for Several Samples

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Table 2 Power Calibration Factors for Laser 2 and Different Objectives

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