激光剥蚀激光诱导击穿光谱分析银首饰中铜杂质
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"Microanalysis of silver jewellery by laser-ablation laser-induced breakdown spectroscopy with enhanced sensitivity and minimal sample ablation"
本文介绍了一种利用激光剥蚀激光诱导击穿光谱法（LA-LIBS）对银首饰中铜杂质进行高灵敏度、小样本消融分析的技术。这种方法基于单一的Nd:YAG激光器，能够实现对银首饰中铜元素的精确检测。通过重激发破裂激光，可以达到6-30倍的信号增强效果，这意味着分析的灵敏度显著提高。同时，空间分辨率仅由消蚀激光的特性决定，而不是由重激发过程影响。
在当前实验条件下，当蚀坑直径为17.2微米时，铜的检测限达到了50ppm。这一技术的关键在于能够在保持相同样本消融量的情况下，提供更高的分析灵敏度，同时减少了对样品的破坏。这对于贵重和易损的银首饰分析尤为重要，因为它允许在不损害样品完整性的前提下获取准确的化学成分信息。
激光诱导击穿光谱法（LIBS）是一种无损分析技术，它利用激光能量产生样品的等离子体，然后通过光谱分析等离子体发射的光来确定样品中的元素组成。LA-LIBS则是LIBS的一种变体，通过激光剥蚀来聚焦和提取样品的一小部分，用于进一步的光谱分析。在本研究中，采用Nd:YAG激光器，这是一种常用的固态激光器，可产生特定波长的激光，适合于材料的消蚀和激发。
该技术的应用不仅限于银首饰，还可以扩展到其他金属合金或珍贵材料的分析，如金、铂等。对于珠宝行业来说，这样的分析方法可以帮助检测和验证首饰的真实成分，确保其品质和价值。同时，它也为材料科学研究提供了强大的工具，可以用来研究金属合金的微观成分变化，以及在不同条件下的腐蚀、老化和热处理效应。
这项工作展示了LA-LIBS在微分析领域的潜力，特别是在高精度和低样本损伤的需求下，对于银首饰和其他类似材料中痕量元素的检测具有重大意义。通过不断优化激光参数和技术，未来可能会实现更高级别的灵敏度和更小的样本需求，进一步推动无损分析技术的发展。
COL 12(8), 083001(2014) CHINESE OPTICS LETTERS August 10, 2014
Microanalysis of silver jewellery by laser-ablation
laser-induced breakdown spectroscopy with enhanced
sensitivity and minimal sample ablation
Junyu Mo (
ddd
), Yuqi Chen (
lll
), Runhua Li (
ooo
ddd
uuu
)
∗
,
Qi Zhou (
±±±
ÛÛÛ
), and Yang Lou (
¢¢¢
)
Department of Physics, School of Science, South China University of Technology, Guangzhou 510641, China
∗
Corresponding author: rhli@scut.edu.cn
Received March 1, 2014; accepted May 20, 2014; posted online July 18, 2014
Laser-ablation laser-induced breakdown spectroscopy (LA-LIBS) based on single Nd:YAG laser is used to
analyze copper impurity in silver jewellery with enhanced sensitivity and minimal sample ablation. 6-30
folds signal enhancement can be achieved under the re-excitation of the breakdown laser and the spatial
resolution is only determined by the ablation laser. 50 ppm limit of detection of copper is achieved when
the crater diameter is 17.2 µm under current experimental condition. This technique gives higher analysis
sensitivity under the same sample ablation in comparison with single pulse (SP) LIBS. It is useful for high
sensitive element microanalysis of precious samples.
OCIS codes: 300.6365, 300.6210, 300.6190.
doi: 10.3788/COL201412.083001.
Laser-induced br e akdown spectroscopy (LIBS) is able
to provide an accurate, in-situ, and quantitative chem-
ical analysis with good sensitivity and spatial reso lu-
tion. With the development of las e r and optoelectronic
detection technologies, the application of LIBS has al-
ready b e e n extended to more and more fields in the past
decades. For example, LIBS has been used to analyze to-
tal nitrogen and phosphorus and heavy metals in soil
[1,2]
.
On multi-elements ana ly sis of precious samples, LIBS
has been used to determine the provenance of different
gem stones and to characterize different jewelleries
[3−5]
.
Quantitative analysis of gold and s ilver alloys by L IBS
has also been reported in literatures
[6−9]
. LIBS is also
applied in the fields of archaeology and art; the analyzed
samples include historic metal artifacts
[10]
, ordnance
[11]
,
Roman silver denarii
[12]
, ancient ceramics
[13]
, fresco
[14]
,
and pigments on painted plasters
[15]
. The common re-
quirement in precious sample analysis mentioned above
was the sample ablation during the analysis had to b e
minimal. In other words, the spatial re solution of LIBS
should be as high as possible.
However, there is a contradiction between analytical
sensitivity and spatial re solution in conventional single-
pulse (SP) LIBS because the sample ablation and break-
down are completed by the same laser pulse. In SP-LIBS,
higher analytical sensitivity usually requires higher laser
energy; on the contrary, higher laser energy will create
bigger craters on the sample surface and deteriorate the
spatial reso lution. Thereafter, it is difficult to analyze
trace elements in the sample with SP-L IBS if high spa-
tial resolution is required a t the same time.
Different efforts have been made to solve this problem.
The first one was the combination of laser-induced fluo-
rescence (LIF) and LIBS, in which the atoms produced in
the laser-induced plasma were resonantly excited by the
second laser and the LIFs of the atoms were monitored
for high sensitive a nalysis
[16−18]
. Chan et al. reported
an interesting method to enhance atomic emission of the
laser-induced plasma, which was termed with r esonance-
enhanced laser-induced plasma spe c troscopy (RELIPS).
In their work, the potassium atoms were resonantly pho-
toionized by a second lase r beam and the sodium emis-
sion at 589 nm was enhanced
[19]
. The techniques of
LIF+LIBS and RELIPS are both able to reduce sample
ablation under the same analytical sensitivity in compar-
ison with SP-LIBS due to the enhanced atomic emissions .
However, these techniques req uire a tunable las er to re-
alize r esonant excitation of the atoms in the plasma.
Dual-pulse (DP) LIBS based on two Nd:YAG lasers
has been established to enhance ana ly tical sensitivity of
LIBS in the past decades
[20−24]
. There are three types of
geometrical arrangements for DP-LIBS: co llinear, cross
beam, and orthogonal. The orthogonal DP-LIBS can be
further classified as pre-ablative
[24]
and reheating
[21,23]
DP-LIBS a ccording to different interpulse time delays.
To achieve better analytical performance, DP-LIBS with
different laser combinations, such as excimer laser plus
Nd:YAG laser
[25]
, C O
2
laser plus Nd:YAG laser
[26]
, fem-
tosecond Ti:Sapphire plus Nd:YAG las e rs have also been
studied
[27]
. In most of the DP-LIBS studies mentioned
above, researchers paid less attention on spatial resolu-
tion improvement than on signal enhancement and two
laser systems were usually required. Antony et al.
[28]
re-
ported a cros s beam DP-LIBS for analysis of lunar sim-
ulant samples in which only single Nd:YAG laser was
required. In their experiment, 532-nm laser from one
Nd:YAG laser was used to abla te sample and 1 064-nm
laser from the same laser was used to r e heating the
plasma to get enhance plasma emission.
This letter will report an application of orthog-
onal dual-wavelength dual-pulse laser-ablation LIBS
(ODWDP LA-LIBS) on the micr oanalysis of copper im-
purity in s ilver jewellery based on single Nd:YAG laser.
In this technique, the 532-nm laser pulse from a Q-
switched Nd:YAG laser was used to ablate small amount
of samples and the 1064 -nm laser pulse from the same
laser was used to break down the ablated samples for
sp e ctral analysis. The propaga tion directions of these
1671-7694/2014/083001(5) 083001-1
c
2014 Chinese Optics Letters
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