Abstract

The unique ability of the ultrafast lasers to perform sub-spot size machining has been proved to be advantageous over conventional lasers for sub-micron-machining. To achieve this, a Gaussian laser beam free of spatial defects is essential. In this research work, submicron holes with clear edge and symmetric shape on thin metal films using a Ti:Sapphire regenerative amplified femtosecond pulsed laser are produced. While analysing, it is observed that there are two shallow pits accompanying the produced hole, symmetrically located at the two sides of the hole, especially when the holes are in the sub-micron range. A careful study on the effects of these shallow pits and the methods to eliminate the same are presented in this letter. It has been concluded that the shallow pits are Rowland ghosts raised by deficiencies of grating space present in the two pairs of gratings used for pulse stretching and compressing. Methods of eliminating these ghosts to achieve features with better edge acuity and quality are also presented.

© Optical Society of America

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References

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  1. X. Liu, "Submicon lines in thin metallic films micromachined by an ultrafast laser oscillator," Technical digest-Conference on Lasers and Electro-Optics 1998, 511 (1998).
  2. P. Bado, W.Clark and A. A. Said, Hand book of look micromachining, (1999), http://www.cmxr.com/micromachining/handbook
  3. P. P. Pronko, S. K. Dutta, J. Squier, J. V. Rudd, D. Du, G. Mourou, "Machining of submicron holes using a femtosecond laser at 800nm," Optics Communications, 114, 106-110 (1995).
    [CrossRef]
  4. X. Liu, D. Du. and G. Mourou, "Laser ablation and micromachining with femtosecond laser pulses," IEEE journal of Quantum Electronics, 33, 1706-1716 (1997).
    [CrossRef]
  5. F. A. Jenkins, H. E. White, Fundamentals of optics, (McGRAW-HILL book company, Singapore 1981)
  6. E. G. Loewen and E. Popov, Diffraction greatings and applications, (Marcel Dekker, INC, New York 1997)

Other

X. Liu, "Submicon lines in thin metallic films micromachined by an ultrafast laser oscillator," Technical digest-Conference on Lasers and Electro-Optics 1998, 511 (1998).

P. Bado, W.Clark and A. A. Said, Hand book of look micromachining, (1999), http://www.cmxr.com/micromachining/handbook

P. P. Pronko, S. K. Dutta, J. Squier, J. V. Rudd, D. Du, G. Mourou, "Machining of submicron holes using a femtosecond laser at 800nm," Optics Communications, 114, 106-110 (1995).
[CrossRef]

X. Liu, D. Du. and G. Mourou, "Laser ablation and micromachining with femtosecond laser pulses," IEEE journal of Quantum Electronics, 33, 1706-1716 (1997).
[CrossRef]

F. A. Jenkins, H. E. White, Fundamentals of optics, (McGRAW-HILL book company, Singapore 1981)

E. G. Loewen and E. Popov, Diffraction greatings and applications, (Marcel Dekker, INC, New York 1997)

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Figures (4)

Fig. 1.
Fig. 1.

Pits created on 1000Å platinum film. (pulse energy of 15nJ, 100 pulses, wavelength of 400nm, pulsewidth of 300fs)

Fig. 2.
Fig. 2.

Rowland ghost measured from first order diffraction of a grating of 100µm-space, illuminated by 632.8nm red laser. Spot diameter of 260µm.

Fig. 3.
Fig. 3.

Pits created on 1000Å platinum film. (pulse energy of 20nJ, 100 pulses, wavelength of 400nm, pulsewidth of 300fs)

Figure 4.
Figure 4.

Pits created on 1000Å platinum film. (pulse energy of 13nJ, 100 pulses, wavelength of 400nm, pulsewidth of 300fs)

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