Abstract

We developed a modified Hoffman contrast technique with a 12ns pulsed incoherent extended white-light source that enables an easily interpretable visualization of ablation plumes with high resolution, a large dynamic range, and color information. By comparison, a conventional dark-field setup with a slitlike laser light source provides large sensitivity but a small dynamic range, and it is difficult to interpret the filtered images.

© 2006 Optical Society of America

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References

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  1. G. S. Settles, Schlieren and Shadowgraph Techniques (Springer, 2001).
    [CrossRef]
  2. A. Vogel and V. Venugopalan, Chem. Rev. 103, 577 (2003).
    [CrossRef] [PubMed]
  3. I. Apitz and A. Vogel, Appl. Phys. A 81, 329 (2005).
    [CrossRef]
  4. H. L. Brode, Phys. Fluids 2, 217 (1959).
    [CrossRef]
  5. N. Arnold, J. Gruber, and J. Heitz, Appl. Phys. A 69, S93 (1999).
    [CrossRef]
  6. R. Hoffman and L. Gross, Appl. Opt. 14, 1169 (1975).
    [CrossRef] [PubMed]
  7. W. Lauterborn and T. Kurz, Coherent Optics (Springer, 2003).

2005 (1)

I. Apitz and A. Vogel, Appl. Phys. A 81, 329 (2005).
[CrossRef]

2003 (2)

A. Vogel and V. Venugopalan, Chem. Rev. 103, 577 (2003).
[CrossRef] [PubMed]

W. Lauterborn and T. Kurz, Coherent Optics (Springer, 2003).

2001 (1)

G. S. Settles, Schlieren and Shadowgraph Techniques (Springer, 2001).
[CrossRef]

1999 (1)

N. Arnold, J. Gruber, and J. Heitz, Appl. Phys. A 69, S93 (1999).
[CrossRef]

1975 (1)

1959 (1)

H. L. Brode, Phys. Fluids 2, 217 (1959).
[CrossRef]

Apitz, I.

I. Apitz and A. Vogel, Appl. Phys. A 81, 329 (2005).
[CrossRef]

Arnold, N.

N. Arnold, J. Gruber, and J. Heitz, Appl. Phys. A 69, S93 (1999).
[CrossRef]

Brode, H. L.

H. L. Brode, Phys. Fluids 2, 217 (1959).
[CrossRef]

Gross, L.

Gruber, J.

N. Arnold, J. Gruber, and J. Heitz, Appl. Phys. A 69, S93 (1999).
[CrossRef]

Heitz, J.

N. Arnold, J. Gruber, and J. Heitz, Appl. Phys. A 69, S93 (1999).
[CrossRef]

Hoffman, R.

Kurz, T.

W. Lauterborn and T. Kurz, Coherent Optics (Springer, 2003).

Lauterborn, W.

W. Lauterborn and T. Kurz, Coherent Optics (Springer, 2003).

Settles, G. S.

G. S. Settles, Schlieren and Shadowgraph Techniques (Springer, 2001).
[CrossRef]

Venugopalan, V.

A. Vogel and V. Venugopalan, Chem. Rev. 103, 577 (2003).
[CrossRef] [PubMed]

Vogel, A.

I. Apitz and A. Vogel, Appl. Phys. A 81, 329 (2005).
[CrossRef]

A. Vogel and V. Venugopalan, Chem. Rev. 103, 577 (2003).
[CrossRef] [PubMed]

Appl. Opt. (1)

Appl. Phys. A (2)

N. Arnold, J. Gruber, and J. Heitz, Appl. Phys. A 69, S93 (1999).
[CrossRef]

I. Apitz and A. Vogel, Appl. Phys. A 81, 329 (2005).
[CrossRef]

Chem. Rev. (1)

A. Vogel and V. Venugopalan, Chem. Rev. 103, 577 (2003).
[CrossRef] [PubMed]

Phys. Fluids (1)

H. L. Brode, Phys. Fluids 2, 217 (1959).
[CrossRef]

Other (2)

G. S. Settles, Schlieren and Shadowgraph Techniques (Springer, 2001).
[CrossRef]

W. Lauterborn and T. Kurz, Coherent Optics (Springer, 2003).

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Figures (5)

Fig. 1
Fig. 1

Schlieren setup with matched pairs of shapes of light sources and filters. Lenses used: Nikon 50 mm 1.2 for collimation, Pentax 50 mm 1.7 as condensor, Nikon 105 mm 2.8 as L 1 , Achromat f = 400 mm as L 2 .

Fig. 2
Fig. 2

Ablation plume produced during water ablation with 80 ns Er:YAG laser pulses ( λ = 2.94 μ m , Φ = 5.4 J cm 2 , spot diameter 0.5 mm ). a, Bright-field image recorded with F = 11 . b, Dark-field image obtained with a 100 μ m filter wire. c, Knife-edge technique, with the lower part of the Fourier plane blocked. d, Knife-edge technique, with filter from above. e, Hoffmann modulation contrast. f, Combined Hoffmann modulation and knife-edge technique, with 1 7 of the image of the light source uncovered. All images were taken 2.3 μ s after the laser pulse and have a size of 5.5 mm × 3.8 mm in object space.

Fig. 3
Fig. 3

Dark-field images of the acoustic transients and ablation plume during skin ablation with a 200 μ s Er:YAG laser pulse ( λ = 2.94 μ m , Φ = 20 J cm 2 , spot size 2.3 mm ), a, 22.5 μ s and b, 40 μ s after the onset of the pulse. Image size: 7.5 mm × 10.0 mm .

Fig. 4
Fig. 4

Water ablation with a 150 ns , 120 mJ thulium laser ( λ = 2.0 μ m ) , photographed 800 ns after the laser pulse by use of the modified Hoffman technique. The radiant exposure and spot size were 6 J cm 2 and 850 μ m in a and 60 J cm 2 and 300 μ m in b. Image size: 3.5 mm × 3.5 mm .

Fig. 5
Fig. 5

Relation between optical resolution and percent cutoff for, a, the knife-edge technique and, b, modified Hoffman modulation contrast. The resolution was determined by using a U.S. Air Force test plate. In a no vertical stripes could be resolved for more than 75% cutoff.

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