Femtosecond laser ablation of carbon reinforced polymers

Femtosecond laser ablation of carbon reinforced polymers

P. Moreno a,b,*, C. Mendez a, A. Garcıa a, I. Arias a, L. Roso a

a Servicio Laser, Universidad de Salamanca, Plaza de la Merced s/n, 37008 Salamanca, Spainb Departamento de Ingenierıa Mecanica, Universidad de Salamanca, Avenida Fernando

Ballesteros s/n, 37700 Bejar, Salamanca, Spain

Received 18 March 2005; received in revised form 7 June 2005; accepted 7 June 2005

Available online 12 July 2005

Abstract

Interaction of intense ultrashort laser pulses (120 fs at 795 nm) with polymer based composites has been investigated. We

have found that carbon filled polymers exhibit different ultrafast ablation behaviour depending on whether the filling material is

carbon black or carbon fiber and on the polymer matrix itself. The shape and dimensions of the filling material are responsible for

some geometrical bad quality effects in the entrance and inner surfaces of drilled microholes. We give an explanation for these

non-quality effects in terms of fundamentals of ultrafast ablation process, specifically threshold laser fluences and material

removal paths. Since carbon fiber reinforced polymers seemed particularly concerned, this could prevent the use of ultrafast

ablation for microprocessing purposes of some of these materials.

# 2005 Elsevier B.V. All rights reserved.

PACS: 79.20.Ds; 42.62.Cf; 61.82.Pv; 78.66.Sq; 81.05.Qk

Keywords: Femtosecond laser ablation; Carbon reinforced polymers; Polyetheretherkethone; Perfluoroalkoxy

www.elsevier.com/locate/apsusc

Applied Surface Science 252 (2006) 4110–4119

1. Introduction

Polymer-based composites exhibit a number of

properties of remarkable interest for many technical

applications. Particularly, carbon filled polymers are

well suited for those requiring some of the following

properties: high mechanical strength, high tempera-

ture performance, some electrical conductivity and

* Corresponding author. Tel.: +34 923 294678;

fax: +34 923 294584.

E-mail address: [email protected] (P. Moreno).

0169-4332/$ – see front matter # 2005 Elsevier B.V. All rights reserved

doi:10.1016/j.apsusc.2005.06.008

high chemical resistance. The industries concerned,

include aerospace, automotive, chemical processing,

medical microdevices and microelectronics, among

others. Focusing on these last two, most of applica-

tions demand high quality and precision microma-

chining of the materials. For many polymers,

conventional chemical structuring techniques, like

etching are precluded and laser ablation is an

alternative method. Commercial nanosecond pulsed

lasers have been extensively used for years to ablate

materials, including polymers [1–3]. For the latter,

laser micromachining is not always satisfactory as a

.

P. Moreno et al. / Applied Surface Science 252 (2006) 4110–4119 4111

result of thermal induced effects, namely, changes in

composition, molten and resolidified material, char-

ring, etc. Femtosecond pulsed laser ablation has been

proven to be a powerful technique to microstructure

practically any material with small thermal damage on

the surface surrounding the ablated areas as compared

to other laser processings [3–5]. Although not fully

understood, the main theoretical basis to explain

ultrafast ablation were already set down elsewhere

[4,6–9]. Today it is well established that there are two

regimes of material removal when intense femtose-

cond laser irradiation of solid targets takes place (see

for instance [10]). The process of ablation is initiated

by non-linear absorption of the radiation within a

surface layer and generation of free electrons by

multiphoton ionization. Obviously, this first step is

reserved for wide bandgap materials. Free carrier

absorption of light helps to increase the number of free

carriers by avalanche ionization up to the critical

density in times shorter than the pulse duration. This is

followed by photoelectron emission and subsequent

surface charging, thermalisation of the electronic

subsystem and energy transfer to the lattice by

electron–phonon coupling, these two last steps

happening in times of the order of some picoseconds,

depending on the material. For fluences slightly above

the ablation threshold and low number of pulses

(< 20–30 pulses), the mechanism for the ejection of

the surface material is Coulomb explosion, thus, being

essentially non-thermal, and therefore, called ‘‘gen-

tle’’ ablation regime. The removal of material (mostly

positive ions) is restricted to some tens nanometers per

pulse and produces smooth surfaces with negligible

thermal damage but very low ablation rates [8]. On the

other hand, for higher fluences, the plasma of free

electrons is overheated and the transfer of energy to

the lattice is much more important. The process is then

basically thermal in nature giving rise to larger

ablation rates (hundreds of nm per pulse) and violent

expulsion of the material (mostly neutral atoms),

associated with a phase explosion mechanism. In

addition, incubation effects begin to play a role when a

large number of pulses irradiate the surface with the

effect of lowering the ablation threshold as a result of

enhanced light absorption resulting from previous

surface modification [11]. Therefore, high fluences

and/or large number of pulses define a different

ablation regime which is known as ‘‘strong’’ ablation

and is more suitable for micromachining purposes

since ablation rates are much higher even though some

more thermal damage around the ablated region

should be expected.

The first works concerning ultraviolet femtosecond

laser ablation of polymers (PMMA and Teflon) were

published in the 1980’s [12,13]. Infrared femtosecond

laser pulses were first applied to the ablation of

polymers 10 years ago [14]. Up to date, few works

have been focused on the study of infrared femtose-

cond laser ablation of polymers (PI, PC, PET and

PMMA [15,16]) and less to ablation of polymer based

composites [17,18]. In this work, we apply femtose-

cond laser pulses to ablate two different commercial

carbon reinforced polymers with respect to the

feasibility of high quality micromachining. We will

show how femtosecond laser micromachining brings

about different features in processed area as a result

of intrinsic differences in the morphology of the

composites and the ablation mechanism itself.

2. Experimental

The materials under investigation differ in the

morphology of carbon filling the polymer as well as

in the polymer matrix. On one hand, carbon fiber

reinforced polyetheretherkethone (PEEK-CF). On the

other, perfluoroalkoxy filled with carbon black (PFA-

CB). All parts were manufactured by injection

moulding, the commercial marks being KETRON

PEEK-CA30 and ZEUS-PFA, respectively. These

composites share a number of outstanding properties,

like high-mechanical strength, thermal conductivity,

wear and chemical resistance and some electrical

conductivity, and they compete in a number of

industrial applications. Electrical conductivity is

achieved by means of the filler, provided the high

resistivity of polymer matrix. Short carbon fibers

filling PEEK matrix amount to 30% of the composi-

tion in our PEEK-CF. PFA-CB consists of many

graphite nanoclusters which form chain structures

(panicles) within the polymer. The content of carbon

black is around 25% for our PFA-CB. The laser

ablation was carried out using a commercial Ti:sap-

phire oscillator (Tsunami, Spectra Physics) and a

regenerative amplifier system (Spitfire, Spectra Phy-

sics) based on chirped pulse amplification (CPA)

P. Moreno et al. / Applied Surface Science 252 (2006) 4110–41194112

Table 1

Ultrafast ablation threshold fluences (100 pulses) for the materials

under investigation

Composite Fth (J/cm2)

PEEK-CF 0.14 � 0.04

PFA-CB 0.44 � 0.13

technique. We produce linearly polarized 120 fs

pulses at 795 nm with a repetition rate of 1 kHz.

The pulse energy can reach a maximum of 1.1 mJ and

is controlled by means of neutral density filters and

measured with a power-meter. The transversal mode is

Gaussian and beam width is 8.5 mm (1=e2 criterion).

The pulses pass through an aperture of variable

diameter before focusing in order to better control the

energy as well as its transversal distribution. The beam

is focused perpendicularly on the target surface

with an achromatic lens doublet with focal length

f ¼ 100 mm. The processing is carried out in air. We

place the parts on a motorized XYZ translation stage,

allowing to pattern microholes, grooves or even more

complex geometries. The morphology and dimensions

of the ablated areas are investigated by means of

optical microscopy (Leica DM ILM) and scanning

electron microscopy (Zeiss DSM940).

3. Results

One can regulate the energy deposited into the

target to ablate an area of desired dimensions and

geometry. To do that, the first step is the evaluation of

the ablation threshold fluence (Fth), i.e. the minimum

energy per irradiated unit area to remove material

from the target. This quantity depends on wavelength,

pulse duration, laser spot size and number of pulses.

We use the well-established method based on the

diffraction of a laser beam by an aperture following

Fig. 1. SEM images of holes drilled with F0 approximately 10� Fth in: (a)

pulses was 1000.

Dumitru et al. [22]. The diffraction pattern (Airy disk

and rings) is focused on the target surface. The

material is damaged where the laser fluence is above

the threshold value. Measurement of the diameter of

the ablated region for different pulse energies with the

help of an electron or optical microscope allows to

determine the ablation threshold fluence. For our

purposes, we are interested in determining the

multishot ablation threshold in air. So far, we irradiate

the material with 100 pulses to overcome the

dependence of threshold fluence on incubation effects

that otherwise are present for smaller number of pulses

as it was stated before [16]. Table 1 shows the

evaluated ablation threshold fluences for the materials

under investigation.

We have irradiated the two composites with

different fluences in order to evaluate the feasibility

of good quality microstructuring of the surfaces, as it

has been demonstrated for many other materials. In

Fig. 1 we show SEM micrographs of holes drilled with

1000 pulses and peak fluences, F0, approximately

10� Fth for each composite: (a) PEEK-CF, and (b)

PFA-CB.

PEEK-CF (1.5 J/cm2), and (b) PFA-CB (3.8 J/cm2). The number of


Fig. 2. Magnification of the wall near the entrance of the hole in the

SEM image of Fig. 1 a, showing waviness. See also the cone-like

sub-micron structures on the wall of the hole.

As it was expected, there is no noticeable evidence

of the typical thermal damage in the surroundings of

the ablated area when the processing is carried out

with longer pulses, like molten material or charring in

the entrance and walls of the holes. Some debris is

deposited around and inside the holes after laser

processing and can be avoided with a more careful

handling of the materials. However, some bad quality

effects are observed, namely, waviness in the entrance

and walls of the holes in PEEK-CF (Fig. 1 a), as well

as significant porosity both in PEEK-CF and PFA-CB

(Fig. 1 b). Whether the observed pores are a result of

processing or not is answered by having a look at the

area around the holes showing porosity in the original

surface. So far, it is inherent to both materials.

Waviness in the entrance and hole walls in PEEK-

CF samples exhibits typical dimensions of 5–10 mm,

and is randomly distributed. These features can be

observed in a magnified SEM micrograph of the hole

entrance (Fig. 2). By contrast, waviness is not present

in holes drilled in PFA-CB (Fig. 1 b), which exhibit

good circular shape in the entrance and quite smooth

walls. Also in Fig. 2 cone-like submicron structures

can be observed in some localized places on the walls

of the hole.

Even though laser fluences had a constant

proportionality to the respective threshold fluences,

we have checked if the absolute fluence plays a

role. Fig. 3 shows that this is not the case and the

same defects are observed for higher peak fluences

Fig. 3. SEM images of holes drilled with 1000 pulses and F0 approximat

cm2). The absolute magnitude of F0 does not play a role in bad geometr

(F0’ 40� Fth) in PEEK-CF (Fig. 3 a) and remain

absent in PFA-CB (Fig. 3 b). Transverse energy

distribution of the laser pulses is not exactly Gaussian

but this cannot explain the origin of edge defects since

they do not appear for PFA-CB.

For the fluences used in our experiments, we are

close or slightly above the air dielectric breakdown

threshold intensities (4� 1013 W/cm2) in the vicinity

of the focus. It has been shown that some distorsion

and deviation of the laser beam resulting from

ely 40� Fth in: (a) PEEK-CF (5.4 J/cm2), and (b) PFA-CB (18.5 J/

ical features in PEEK-CF as compared to PFA-CB.


scattering with induced plasma as well as absorption

have to be expected for the incoming pulses [19]. The

main geometrical effect is some widening of the hole

which increases with the intensity. However, it has

been reported that, for high number of pulses,

intensities slightly above the air breakdown threshold

and gaussian energy distributions, the circular shape is

not much affected [19–21]. This is confirmed looking

at the circular shape of the hole in PFA-CB (Fig. 3 b)

where intensity is approximately three times the air

breakdown threshold.

Fig. 4. SEM snapshots of the progress of ablation in PEEK-CF for increas

fluence (F0 ¼ 5:4 J/cm2) ablates polymer matrix surrounding carbon fi

unaffected. Above 20 pulses, the polishing effect on the surface of carbo

4. Discussion

So far, all evidence points out the materials

themselves—and not the laser processing para-

meters—to be responsible of uneven behaviour of

both composites. For the processing parameters, even

though ‘‘gentle’’ and ‘‘strong’’ ablation are always

competing processes, the effects of ‘‘strong’’ removal

are much more important. An explanation based on the

existence of different removal regimes is, therefore,

not suitable. Polymer matrix has different composition

ing number of pulses: (a) 2; (b) 4; (c) 10; (d) 20; (e) 50; (f) 90. Laser

bers from the leading pulses while carbon fiber remains almost

n fibers is noticeable.


Fig. 5. Magnification of the innerside of the ablated area in: (a) PEEK-CF, and (b) PFA-CB. The number of laser pulses is 90 and F0 is

approximately 40� Fth for both materials. Case (a) shows the fibers remaining after polymer has been ablated around and the effect of fiber

polishing after some laser pulses. Case (b) shows how the graphite fills the polymer matrix in the form of panicles and is therefore removed

together with the ablated polymer.

for the materials under investigation but this should

affect exclusively to the amount of laser energy

needed to induce ultrafast ablation and should not

affect the geometrical quality of the holes.

Regardless of the amount of carbon in the

composition of both samples, the morphology is

different as we have already remarked. This fact will

help to explain that while PFA-CB is microstructured

with high geometrical quality, PEEK-CF is not.

4.1. Poor quality effects

We have monitored the progress of the ablation

process for the first pulses impinging on the surface of

the material. Fig. 4 shows a series of SEM snapshots

of the irradiated area on PEEK-CF surface for

increasing number of laser pulses, from 2 to 90,

and the same fluence as of Fig. 3 a. At first glance, we

observe the presence of carbon fibers within the

irradiated area. A thorough analysis of the images

provides with more outstanding facts. For the first

pulses (Fig. 4 a–d), these carbon fibers seem to be

almost unaffected by laser pulses while the polymer is

removed. As a result, the irradiated area resembles a

‘‘devastated greek temple’’ landscape. As more

pulses impinge on the material, the hole deepens

but some fibers remain still bound to the polymer

matrix. Meanwhile, some polishing of the fibers

surfaces arises for 20 pulses and on (Fig. 4 e and f). As

a matter of fact, this effect becomes more pronounced

as the number of pulses increases. The magnification

of the inner side of the hole shows better this effect

(Fig. 5 a).

The question is why these fibers remain within the

hole for the first pulses and are absent after irradiation

with 1000 pulses (Fig. 3 a) and how is this related to

the poor geometrical effects observed in PEEK-CF.

Moreover, why PFA-CB does not exhibit such non-

quality effects.

Most of the materials consists of more than one

type of atoms or molecules. However, one can

consider a unique ablation threshold fluence since

the distribution of the species is often homogeneous.

That means either we have a collective multiphoton

ionization threshold or that the removal of the most

common component is able to drag the rest of the

components as a result of bonds. The size, geometrical

shape and distribution of the filling material in

composites is the key to understand the ultrafast laser

ablation of these non-chemically bound materials. On

one hand, carbon black in PFA-CB has typical

dimensions well below 1 mm and is homogeneously

distributed inside the polymer matrix (Fig. 5 b). In our

experiments, the size of the irradiated area where laser

fluence is above measured ablation threshold is

typically 40–50 mm. So far, PFA-CB behaves as most

of the materials do, since ablation of polymer matrix

drags small graphite particles.


By contrast, carbon fibers in PEEK-CF have

sections in the order of 5–10 mm and lengths of

10–20 mm and are not homogeneously distributed.

For typical processing conditions, we have actually a

two-fold threshold material. The remnant carbon

fibers within the hole drilled after irradiation suggest

that the polymer is preferentially removed from the

composite at least for the first pulses (Fig. 4). This

selective removal of polymer matrix was reported

before for nanosecond pulsed XeCl laser ablation of

long carbon fiber reinforced PEEK [23].

We will try to understand this selective ablation in

the next subsection but whatever its origin, it is

sufficient to explain the absence of carbon fibers after

irradiation with large number of pulses as well as poor

geometrical quality of the ablated structures. Regard-

less of the processes affecting the carbon fibers it is

evident from Fig. 4 that polymer removal is the main

responsible for the deepening of the hole. The deeper

the hole the more difficult for the fibers left behind to

keep tied to the polymer matrix, and are either

vaporized or, more easily, pulled out mechanically by

the plasma originated from polymer ablation and

ejected at very high speeds. Observation of the

products of ablation shows that many fibers are ejected

practically unaffected (Fig. 6 a). As a consequence,

after some hundreds of pulses, there is no trace of

carbon fibers within the hole (Figs. 1 a and 3 a).

Additionally, we can observe that some fibers are

placed partially outside the ablated region (Figs. 6 b or

Fig. 6. SEM images of: (a) a large fragment of carbon fiber ejected during a

Fig. 1 a and 100 pulses. The presence of a carbon fiber partially placed out

soon as the fiber is dragged out.

4 d). Following the previous explanation, we should

expect the fibers to be pulled out after some laser

pulses. In such a case, the fiber leaves a cavity in the

hole edge or wall which is the ‘‘negative’’ of the

portion outside the ablated region. This is our

explanation for the waviness observed in the hole

entrance and walls in Figs. 1 a or 3 a.

4.2. Preferential ablation of the polymer in

PEEK-CF

Comparing Fig. 4 a and d, one can observe that the

diameter of the ablated region increases with the

number of pulses up to the 20th pulse, and then

stabilizes. It has been reported before [16] that this

effect is the result of incubation processes and

consequent decrease of the ablation thresholds. Since

the peak pulse fluence is the same for all the pulses

used for the processing, this means that the energies of

the first pulses are not that far above the threshold, and

ablation takes place in the ‘‘gentle’’ ablation regime.

Thus, the low ablation rates observed for the first

pulses and the smaller diameters of the hole. For larger

number of pulses, the ratio between peak and

threshold fluence grows, the process coming into

the ‘‘strong’’ removal regime. Therefore, the larger

ablation rates and faster deepening of the hole, as well

as increasing diameter.

Yet we have to explain why the preferential

ablation of the polymer matrix. The most simple

blation, and (b) the edge of a hole drilled with the laser parameters of

side the ablation region will leave a cavity on the wall of the hole as


explanation could be a large difference between

polymer and carbon fiber ablation thresholds and/or

rates. If this were the case, then peak pulse fluences

used in our experiments could be far above polymer

threshold but below or slightly above carbon fiber

threshold and thus explain why fibers remain on the

basis of non-existing or small ablation rates as

compared to polymer matrix ablation rates. The effect

should be more noticeable in the hole edges as a result

of the gaussian energy profile of the pulses.

However, it has been stated in previous works [24]

that the multishot femtosecond ablation threshold of

highly orientated (crystalline) pyrolithic graphite

(HOPG) is 0.15–0.30 J/cm2 which is very close to

our measured threshold for PEEK-CF. This would lead

to think that the polymer and the filler should undergo

similar ablation processes but this is not the case as we

have already shown in Fig. 4. To shed some light, we

propose two complementary explanations for the

preferential ablation of the polymer, the first one based

on the effect of polarization on the effective ablation

threshold and rates of carbon fibers and the second

relying on the thermal effects derived of the large

number of pulses and fluences used in the experi-

ments.

4.2.1. Influence of polarization on carbon fiber

ablation

HOPG structure consists of parallel planes of

carbon atoms. Anisotropic thermal and electrical

conductivity of graphite is determined by the

delocalised electrons whose motion preferentially

takes place in those planes. Determination of

femtosecond ablation threshold of HOPG in the

literature was carried out by irradiation of the surface

of graphite films with normal incidence to those

carbon planes. Therefore, the electric field oscillates in

the same plane where electrons move more easily

whatever the polarization of the incident field.

Carbon fibers are amorphous materials, contrarily

to HOPG films. They consist of many short, often

folded and quite disordered chains of graphite crystals,

the more intricate the structure the deeper inside the

fiber. In addition, short fibers inside PEEK-CF are

randomly distributed and orientated. Provided the

linear polarization of our pulses, the incidence angle

on the surface of each fiber become very important

concerning the absorption of light and consequent

ablation of the graphite on the surfaces. Maximum

absorption will take place for normal incidence to the

graphite planes. However, the short range order within

carbon fibers makes absorption and therefore ablation

to be extremely dependent both of the orientation of

the fiber and of the area irradiated within each fiber

surface. Even if the more external layers are ablated,

the structure of the fibers become more intricated the

deeper inside the fiber, being more and more difficult

to remove layers. Recently, Kocabas et al. [25]

reported selective ablation of carbon nanotubes

depending on the nanotube axis orientation with

regard to polarization direction, concluding the

dependence of the ablation threshold with orientation.

They found that nanotubes aligned with the polariza-

tion direction were more easily ablated than those

perpendicular.

Focusing on an isolated carbon fiber, it would be

therefore complicated to define an ablation threshold

since the remotion of material would strongly depend

on the local orientation of the graphite crystals with

regard to incidence angle of light. In our PEEK-CF,

short carbon fibers are randomly distributed and

orientated, leading to additional dependence on the

fiber orientation. The overall effect, however, would

be a less efficient absorption of femtosecond pulses

and consequently larger effective ablation threshold

and smaller ablation rates. This is a likely explanation

for the slight ablation of fibers observed in Fig. 4.

4.2.2. Role of thermal effects in ablation of the

polymer

Another complementary explanation for preferen-

tial ablation can be proposed on the basis of the

thermal nature of femtosecond ablation for the

fluences used in our experiments, remarkably after

some pulses. In this case, thermal properties of the

components should play a decisive role. Ablation rates

of the polymer matrix could be increased spectacu-

larly as a result of indirect thermal ablation provided

the far different thermal properties of the components.

These indirect processes were already pointed out in

[17,26] for the ablation of elastomer–carbon compo-

sites with UV and infrared nanosecond pulsed lasers.

Carbon fibers in PEEK-CF can absorb energy

during the process from different sources: laser

radiation, plasma radiation, and collision with the

products of polymer ablation (electrons, ions, atoms,


dragged carbon fibers). It is well known that polymers

melt or decompose with relatively low temperatures

(for PEEK, 613 K) while carbon melts slightly below

4000 K and vaporizes above 5000 K. In addition,

thermal conductivity and diffusivity are more than two

orders of magnitude larger for carbon than for PEEK

[27]. Therefore, ablation rates could be enhanced

for PEEK as a result of heat transfer from carbon

fibers and lower temperature requirements to melt or

vaporize as compared to carbon fibers.

Shortly, carbon fibers undergo different processes

during irradiation. On one hand, direct laser ablation

that removes material from their surfaces like any

other material. On the other hand, part of the absorbed

laser energy as well as energy contribution from PEEK

ablation (plasma radiation and collision with ablation

products) contribute to heat the fibers. This heat could

melt or vaporize at least a surface layer of the fibers

while partially is employed to heat the polymer

around, which quickly melts and/or decomposes and

finally is ejected.

4.3. Formation of conical submicron structures

We will say some words about the cone-like

submicron structures observed in PEEK-CF (Fig. 2)

that we have reported to appear in some localized places

on the walls of the holes. In [26], the authors reported

the formation of conical structures on the ablated

surface of elastomer–carbon composites processed

with excimer and nanosecond pulsed Nd:YAG lasers.

Shortly, their explanation was that, as a result of laser

ablation, some carbon particles are redeposited on the

composite surface. Provided the thermal properties of

carbon, these particles act as shields, preventing

ablation of the material below. In our case, carbon

nanoparticles can be ejected as a result of ablation and

deposited on the surface of the composite. In fact, we

have reported cone-like structures on the hole walls but

also on traces of polymer still covering carbon fibers.

Given the high fluences used, we could expect some

kind of similar shielding effect in localized places on

the surface of the composite preventing indirect thermal

ablation of the material underlying. The submicron size

of these structures can be attributed to the size of the

ablated carbon nanoparticles, that are well known to be

smaller than those produced in nanosecond laser

ablation.

5. Conclusions

Geometrical quality of micromachined structures

in polymer based composites by ultrafast laser

ablation is strongly dependent of the type, dimen-

sions and distribution of filling material within

the polymer matrix. We have shown that carbon

black filled polymers can be processed by means of

femtosecond intense pulsed lasers as many other

materials, giving rise to very good quality structures.

On the contrary, microholes ablated in carbon fiber

reinforced polymers exhibit bad quality effects, like

waviness and irregular shapes as a result of fiber

dimensions and preferential ablation of the polymer.

We propose a two-fold explanation for the latter on

the basis of indirect thermal processes resulting from

energy absorption by the carbon fibers and transfer to

the surrounding polymer as well as polarization

effects on the ablation thresholds and rates of carbon

fibers.

Carbon filled polymers are materials widely

used in industry. Their use for microtechnology

purposes will require high-quality microstructuring

techniques. As we have demonstrated, ultrafast laser

ablation can provide good micromachined structures

in some carbon reinforced polymers, namely,

carbon black filled polymers, but not in another

important family, like fiber reinforced ones. As far as

we know, these composites are the first materials

which exhibit bad quality as they are processed

with femtosecond lasers. These non-quality effects

are not dependent of process parameters and could

be only surpassed by changing the choice of mat-

erial.

Acknowledgements

We acknowledge financial support from the

Ministerio de Ciencia y Tecnologıa de Espana (project

BFM2002-00033), the Junta de Castilla y Leon

(project SA107/03), and the Fundacion Memoria de

Samuel Solorzano Barruso. We also thank the Servicio

de Microscopıa Electronica, Universidad de Sala-

manca, specially Dr. Juan Gonzalez Julian, for SEM

images and Eladio Mendoza from the Laboratorio de

Mecanica de Fluidos, Universidad de Sevilla for

supplying materials.


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Femtosecond laser ablation of carbon reinforced polymers

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