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Near infrared ultra-fast intense laser-induced colour centres in KCl crystal
ARTICLE IN PRESS
Journal of Crystal Growth 263 (2004) 648–649
Letter to the editor
Near infrared ultra-fast intense laser-induced colour centres in KCl crystal Shoukui Pan*, Benxue Jiang, Xiongwei Jiang, Jiangrong Qiu, Congshen Zhu Proton Craft Project, Shanghai Institute of Optics and Fine Mechnics, AcademiaSinica, P.O.Box 800211, Shanghai 201800, China
In general, alkali halide crystal is transparent in the range of visible light. When the samples of alkali halide crystals were subject to an appropriate chemical or physical treatment, they will acquire a distinctive colour. The colouring of the samples results from distortions of the crystalline structure known as colour centres. Usually, the physical treatment method is to carry out an irradiation process of rays to the sample of alkali halide crystal using ultraviolet-rays, X-rays, gamma-rays or electron beam. After the sample was irradiated, the colour centres were formed uniformly throughout the sample so that uniform colouring was also found throughout the entire sample. Since mid-1990’s, people have been strongly interested in the research works on the interaction between the ultra-fast intense laser and transparent materials (e.g. glass) by irradiation of the focused femtosecond laser beam [1, 2]. A lot of experiments [3–5] have evidenced that the ultrafast intense laser can induce the microscopic modification of glass structure in the interacted area resulting in performance change. These results express that using the femtosecond laser technique can realize the space-selective performance change in a minute area of a bulk of glass material. Recently, a sample of KCl crystal (4 4 4 mm3) was irradiated by a 800 nm,120 fs *Corresponding author. E-mail address: [email protected] (S. Pan).
and 1 kHz Ti:sapphire laser beam with average power 14–48 mw in our group. This laser beam was focused onto a spot size of about 10 mm and on a plane 100 mm below the surface of the sample by a microscope with a 5 objective lens and a numerical aperture of 0.8. Space-selective induced colour centres were formed. The black areas (realistic colour is blue) in Fig. 1 are the colour centres area formed by the scanning of femtosecond laser beam with different power. Fig. 2 is an absorption spectrum of the colour centres area, in which the positions of absorption peaks from short wavelength to long wavelength correspond to the V3, F, R1, R2, M and N centres in KCl crystal. From this result we conclude:
Fig. 1. Space-selective colour centre areas in KCl crystal by irradiation of near infrared ultra–fast intense laser beam. The dark level of colour depends on the irradiation power.
0022-0248/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2003.12.051
ARTICLE IN PRESS S. Pan et al. / Journal of Crystal Growth 263 (2004) 648–649
2.4 2.1
F 551nm
V3 231nm
Absorption
1.8 R2 740nm
1.5 1.2
673nm R1
0.9
M 822nm N 962nm
0.6 0.3 200
400
600 800 Wavelength/ nm
1000
1200
Fig. 2. Absorption spectrum of the colour centre areas in KCl crystal with JASCO V-570 absorption spectrometer.
(1) We first reported that the colour centres in alkali halide crystal can be formed by the irradiation of near infrared ultra-fast intense laser beam. (2) The colour centres in alkali halide crystal can be space-selective formed by the irradiation technique of ultra-fast intense laser. As we know, the alkali halide crystal with colour centres is one type of laser crystal. Thus, people can use this technique to fabricate the microstructural material with laser function by selecting a suitable alkali
649
halide crystal for the application (as a microoptical element) in all-optical circuits. (3) From No. 2 conclusion above, we consider that though one thinks that the glass structure is more flexible than that of crystal structure, some types of crystalline material, which need us to open up, also can be selected as a research object in the scope of photo-induced microscopic modification of material structure by ultra-fast intense laser. So exploring function microstructure of crystalline material is possible and also is an event with potential application value in integrated optical circuits. This project is supported by Natural Science Foundation of China, Contract No. 60178026 and 60378033.
References [1] K.M. Davis, K. Miura, et al., Opt. Lett. 21 (21) (1996) 1729. [2] K. Miura, J. Qiu, et al., Appl. Phys. Lett. 71 (1999) 3329. [3] J. Qiu, M. Kawasaki, et al., J. Phys. Chem. Solids 159 (9) (1998) 1521. [4] K. Muira, J. Qiu, T. Misuyu, Opt. Lett. 25 (6) (2000) 408. [5] J. Qiu, C. Zhu, et al., Appl. Phys. Lett. 79 (2001) 3567.
Journal of Crystal Growth 263 (2004) 648–649
Letter to the editor
Near infrared ultra-fast intense laser-induced colour centres in KCl crystal Shoukui Pan*, Benxue Jiang, Xiongwei Jiang, Jiangrong Qiu, Congshen Zhu Proton Craft Project, Shanghai Institute of Optics and Fine Mechnics, AcademiaSinica, P.O.Box 800211, Shanghai 201800, China
In general, alkali halide crystal is transparent in the range of visible light. When the samples of alkali halide crystals were subject to an appropriate chemical or physical treatment, they will acquire a distinctive colour. The colouring of the samples results from distortions of the crystalline structure known as colour centres. Usually, the physical treatment method is to carry out an irradiation process of rays to the sample of alkali halide crystal using ultraviolet-rays, X-rays, gamma-rays or electron beam. After the sample was irradiated, the colour centres were formed uniformly throughout the sample so that uniform colouring was also found throughout the entire sample. Since mid-1990’s, people have been strongly interested in the research works on the interaction between the ultra-fast intense laser and transparent materials (e.g. glass) by irradiation of the focused femtosecond laser beam [1, 2]. A lot of experiments [3–5] have evidenced that the ultrafast intense laser can induce the microscopic modification of glass structure in the interacted area resulting in performance change. These results express that using the femtosecond laser technique can realize the space-selective performance change in a minute area of a bulk of glass material. Recently, a sample of KCl crystal (4 4 4 mm3) was irradiated by a 800 nm,120 fs *Corresponding author. E-mail address: [email protected] (S. Pan).
and 1 kHz Ti:sapphire laser beam with average power 14–48 mw in our group. This laser beam was focused onto a spot size of about 10 mm and on a plane 100 mm below the surface of the sample by a microscope with a 5 objective lens and a numerical aperture of 0.8. Space-selective induced colour centres were formed. The black areas (realistic colour is blue) in Fig. 1 are the colour centres area formed by the scanning of femtosecond laser beam with different power. Fig. 2 is an absorption spectrum of the colour centres area, in which the positions of absorption peaks from short wavelength to long wavelength correspond to the V3, F, R1, R2, M and N centres in KCl crystal. From this result we conclude:
Fig. 1. Space-selective colour centre areas in KCl crystal by irradiation of near infrared ultra–fast intense laser beam. The dark level of colour depends on the irradiation power.
0022-0248/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2003.12.051
ARTICLE IN PRESS S. Pan et al. / Journal of Crystal Growth 263 (2004) 648–649
2.4 2.1
F 551nm
V3 231nm
Absorption
1.8 R2 740nm
1.5 1.2
673nm R1
0.9
M 822nm N 962nm
0.6 0.3 200
400
600 800 Wavelength/ nm
1000
1200
Fig. 2. Absorption spectrum of the colour centre areas in KCl crystal with JASCO V-570 absorption spectrometer.
(1) We first reported that the colour centres in alkali halide crystal can be formed by the irradiation of near infrared ultra-fast intense laser beam. (2) The colour centres in alkali halide crystal can be space-selective formed by the irradiation technique of ultra-fast intense laser. As we know, the alkali halide crystal with colour centres is one type of laser crystal. Thus, people can use this technique to fabricate the microstructural material with laser function by selecting a suitable alkali
649
halide crystal for the application (as a microoptical element) in all-optical circuits. (3) From No. 2 conclusion above, we consider that though one thinks that the glass structure is more flexible than that of crystal structure, some types of crystalline material, which need us to open up, also can be selected as a research object in the scope of photo-induced microscopic modification of material structure by ultra-fast intense laser. So exploring function microstructure of crystalline material is possible and also is an event with potential application value in integrated optical circuits. This project is supported by Natural Science Foundation of China, Contract No. 60178026 and 60378033.
References [1] K.M. Davis, K. Miura, et al., Opt. Lett. 21 (21) (1996) 1729. [2] K. Miura, J. Qiu, et al., Appl. Phys. Lett. 71 (1999) 3329. [3] J. Qiu, M. Kawasaki, et al., J. Phys. Chem. Solids 159 (9) (1998) 1521. [4] K. Muira, J. Qiu, T. Misuyu, Opt. Lett. 25 (6) (2000) 408. [5] J. Qiu, C. Zhu, et al., Appl. Phys. Lett. 79 (2001) 3567.