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We propose a cost-effective high-pulse energy supercontinuum (SC) source based on a telecom range diode laser-based amplifier and a few meters of standard single-mode optical fiber, with a pulse energy density as high as ~25 nJ/nm in the 1650-1850 nm regime (factor >3 times higher than any SC source ever used in this wavelength range). We demonstrate how such an SC source combined with a tunable filter allows high-resolution spectroscopic photoacoustic imaging and the spectroscopy of lipids in the first overtone transition band of C-H bonds (1650-1850 nm). We show the successful discrimination of two different lipids (cholesterol and lipid in adipose tissue) and the photoacoustic cross-sectional scan of lipid-rich adipose tissue at three different locations. The proposed high-pulse energy SC laser paves a new direction towards compact, broadband and cost-effective source for spectroscopic photoacoustic imaging.
In this Letter, we demonstrate a high pulse energy and linearly polarized mid-infrared Raman fiber laser targeting the strongest absorption line of
C
O
2
at
∼
4.2
µ
m
. This laser was generated from a hydrogen (
H
2
)-filled antiresonant hollow-core fiber, pumped by a custom-made 1532.8 nm Er-doped fiber laser delivering 6.9 ns pulses and 11.6 kW peak power. A quantum efficiency as high as 74% was achieved, to yield 17.6 µJ pulse energy at 4.22 µm. Less than 20 bar
H
2
pressure was required to maximize the pulse energy since the transient Raman regime was efficiently suppressed by the long pump pulses.
We demonstrate a simple and power stable 1.5–10.5 µm cascaded
mid-infrared 3 MHz supercontinuum fiber laser. To increase simplicity
and decrease cost, the design of the fiber cascade is optimized so
that no thulium amplifier is needed. Despite the simple design with no
thulium amplifier, we demonstrate a high average output power of
86.6 mW. Stability measurements for seven days with 8–9 h operation
daily revealed fluctuations in the average power with a standard
deviation of only 0.43% and a power spectral density stability of
±
0.18
d
B
m
/
n
m
for wavelengths
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