JOURNAL OF ELECTRONIC SCIENCE AND TECHNOLOGY, VOL. 13, NO. 1, MARCH 2015
73
Abstract⎯During the last few decades, photothermal
radiometry (PTR) has been greatly developed and
widely applied in the field of nondestructive testing.
However, the traditional PTR system employs an
expensive lock-in amplifier to detect the weak
photothermal signal, which leads to high cost and long
test time. In this paper, a fast transmission PTR system
based on sampling by using an internal computer sound
card was developed to lower the system cost and shorter
the test time. A piece of amorphous silicon (a:Si) thin
film solar cells with artificial defects was prepared and
tested by the system. The results show that the
sharpened defects can be identified easily and quickly
according to the significant peaks of the original
infrared signal sampled by the internal computer sound
card. Furthermore, more detailed defects can be
investigated by processing the infrared signal. These
validate the effectiveness of the proposed transmission
PTR system as a low cost and efficient non-destructive
test technique.
Index Terms⎯Amorphous silicon thin film solar cells,
internal computer sound card, nondestructive testing,
transmission photothermal radiometry.
1. Introduction
In 1979，photothermal radiometry (PTR), based on
“photoacoustic effect”, was first introduced by Nordal and
Kanstad who are two of the most famous scientists in the
Manuscript received March 31, 2014, revised May 16, 2014. This work
was supported by the National Natural Science Foundation of China under
Grant No. 61379013 and the Excellent Doctoral Academic Support
Program under Grant No.YBXSZC2013021.
L.-J. Yan is with the School of Optoelectronic Information, University
of Electronic Science and Technology of China, Chengdu 610054, China
(e-mail: laijun11-11@163. com)
C.-M. Gao is with the School of Optoelectronic Information, University
of Electronic Science and Technology of China, Chengdu 610054, China
(Corresponding author e-mail: gaocm@uestc.edu.cn).
B.-X. Zhao, Q.-M. Sun, and F. Wang are with the School of
Optoelectronic Information, University of Electronic Science and
Technology of China, Chengdu 610054, China (e-mail:
zhaobxing@uestc.edu.cn; pavel_sun@sina.com; wangfeeng@163.com).
Digital Object Identifier: 10.3969/j.issn.1674-862X.2015.01.013
field of photoacoustic and photothermal phenomenon
[1]
.
During the last few decades, the PTR technique has been
greatly developed and extensively studied worldwide drawn
by its high sensitivity, high security, and high resolution.
The PTR technique has been widely applied in the field of
nondestructive testing, including surface cracks imaging
[2]
,
deep subsurface defects detection
[3]
, hairline crack
detection
[4]
, quantitative evaluation of the kinetics of human
enamel simulated caries
[5]
, industrial steel hardness
inspection
[6]
, thermal diffusivity determination of
polymerized dental resins
[7]
, properties characterization of
semiconductor materials
[8],[9]
, and thermal conductivity
measurement of thin films
[10]
and surface roughness
investigation
[11]
. However, an expensive lock-in amplifier
was adopted in the traditional PTR system to detect the
weak photothermal signal
[2]−[11]
, which resulted in high
system cost and long test time. To lower the system cost
and shorten the test time, a fast transmission PTR system
based on sampling by an internal computer sound card (also
known as an audio card) is introduced in this paper. The
signals, whose frequency range is 10
Hz to 20
kHz and
amplitude is lower than 1.5
V, can be sampled by the
internal computer sound card. The sample rate of the
internal computer sound card can be up to 96
kHz and the
sample resolution is 16
bits or 20
bits, or even 24
bits for
some advanced sound cards. It was reported that an internal
computer sound card was applied in signal processing in a
photoacoustic system
[12]
. Thus the internal computer sound
card is also qualified enough for photothermal signal
detection in a PTR system, which means that there is no
need to use an extra expensive lock-in amplifier.
2. Theoretical Consideration
A 3-dimentional (3D) simplified transmission PTR
model is shown in Fig. 1. A single layer sample of optically
opaque material, with the thickness of l, is surrounded by
air. A laser beam with the intensity I
0
and angular
modulation frequency ω=2πf is impinged on the front
surface of the sample, which absorbs light on its surface.
Because the sample studied here is a piece of amorphous
silicon thin film solar cells, there will be both radiative
recombination and non-radiative recombination when the
sample absorbs the laser. Photo-carrier radiometry
Fast Transmission Photothermal Radiometry via
Sampling by an Internal Computer Sound Card
Lai-Jun Yan, Chun-Ming Gao, Bin-Xing Zhao, Qi-Ming Sun, and Feng Wang
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