Photo-physical mechanism of near-IR femtosecond laser-induced refractive-index change in PMMA

被引：1

作者：

Kudryashov, Sergey ^{[1
,2
]}

Gulina, Yulia ^{[1
,2
]}

Danilov, Pavel ^{[1
,2
]}

Smirnov, Nikita ^{[1
,2
]}

Rimskaya, Elena ^{[1
,2
]}

Krasin, George ^{[1
,2
]}

Saraeva, Irina ^{[1
,2
]}

Shelygina, Svetlana ^{[1
,2
]}

Rupasov, Alexey ^{[1
,2
]}

Pershin, Kirill ^{[1
,3
,4
]}

Tsygankov, Alexander ^{[1
,3
]}

Gorevoy, Alexey ^{[1
,2
]}

机构：

[1] Bauman Moscow State Tech Univ, Moscow 105005, Russia

[2] Russian Acad Sci, PN Lebedev Phys Inst, Moscow 119991, Russia

[3] Excimer Eye Clin, Moscow 109147, Russia

[4] Fed Med Biol Agcy, Acad Postgrad Educ, Moscow 125371, Russia

来源：

OPTICS LETTERS | 2025年 / 50卷 / 01期

关键词：

WAVE-GUIDES;

D O I：

10.1364/OL.547650

中图分类号：

O43 [光学];

学科分类号：

070207 ; 0803 ;

摘要：

Micromodification in bulk undoped polymethylmethacrylate (PMMA) by single focused (numerical aperture (NA) = 0.25), 1030-nm 250-fs laser pump pulses was explored by pump self-transmittance; optical, 3D-scanning confocal photoluminescence (PL); Raman micro-spectroscopy; and optical polarimetric and interferometric microscopy. Starting from the threshold pulse energy E-th = 0.4 +/- 0.1 mu J (peak laser intensity I-th approximate to 8 TW/cm(2)), visible bright micro-voxels emerged inside PMMA at the 100 divided by 300-mu m depth, with their PL-acquired dimensions increasing versus pulse energy. Optical phase change was interferometrically measured in the voxels at the 532-nm wavelength, exhibiting versus the pulse energy the isotropic refractive index increase Delta n = +(4 divided by 10) x 10(-4), and a new 1640-cm(-1) peak of C=C vibrations emerged in the Raman spectra. Pump self-transmittance measurements demonstrated the predominating eight-photon absorption (excited energy level approximate to 9.7 eV, coefficient beta(8) approximate to 3 x 10(-5) cm(13)/TW7) at the sub-threshold I < I-th, implying photoionization of the PMMA chains (the ionization potential of MMA molecule approximate to 9.7 eV). At higher peak intensities I > I-th, inverse brems-strahlung absorption (coefficient similar to 10(3)cm(-1)) of near-critical micro-plasma (density >5 x 10(20) cm(-3)) predominates over the multi-photon PMMA absorption, providing the bulk energy density >6 x 10(2) J/cm(3) and the temperature rise Delta T > 2.2 x 10(2) K, which are sufficient for PMMA (de)polymerization near the equilibrium bulk temperature T-P approximate to 220 degrees C. These results uncover the quantitative mechanism of fs-laser modification of PMMA, justifying the previous qualitative findings and enabling controllable energy deposition during fs-laser PMMA micromachining of diverse functional applications. (c) 2024 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.

引用

页码：129 / 132

页数：4