We demonstrate a lithium triborate (LBO) optical parametric oscillator (OPO), which is synchronously pumped with a
pulse-compressed and frequency-doubled master-oscillator power-amplifier (MOPA) system consisting of a gain-switched
laser diode and a series of Ytterbium-doped fiber amplifiers. The 20ps pulses from the MOPA were
compressed in a transmission grating compressor down to 4.4ps with a throughput efficiency of ~70% and subsequently
frequency-doubled with an efficiency of ~60% in a 20mm long LBO to a maximum of ~25W. With a typical pump
power of 17W for the OPO, we obtained a maximum combined signal and idler output power of 2.5W (at 877nm) and
1.7W (at 1.3μm). Individually, a maximum signal power of up to 3.7W at 740 nm was obtained with a signal pulse
duration of ~3.2ps. The OPO was widely tunable from 651nm-1040nm (signal) and from 1081nm-2851nm (idler). To
the best of our knowledge, this is the highest output power from a green-pumped LBO OPO. The fiber-based pump
source can potentially be operated between 100MHz and 1GHz, which in combination with the few-picosecond pulses
and the near-IR tunability of the OPO is a very attractive source for nonlinear microscopy.
We report a large aperture PPMgLN based OPO generating 21W of average output power at a slope efficiency of 45%,
pumped by the output from a polarization maintaining Ytterbium doped fiber MOPA operating at 1060nm producing
58W of average output power and 20ns pulses at a repetition rate of 100kHz. A maximum of 5.5W of optical power was
recorded at the idler wavelength of 3.82μm without thermal roll-off. We have experimentally verified that the pulse
rise/fall time plays a significant role in the OPO conversion efficiency and that further enhancement in the OPO
conversion efficiency will be possible using sub-nanosecond rise and fall times.
We report the simultaneous excitation of multiple Raman Stokes lines in a 250 m long fiber using multi-step pump
pulses. The frequency doubled output of a single polarization all-fiber Yb-doped MOPA operating at 1060 nm was used
as the pump source. By adjusting the pump power and the pulse profiles we achieved the simultaneous excitation of
green (1st Stokes), yellow (4th Stokes) and red light (6th Stokes) using 3-step pulses or the combination of any two using
2-step pulses. Through the use of pulse shaping we generate sequences of colored pulses with the flexibility of providing
dynamic, agile frequency tuning between well-defined wavelengths.
We report the realisation of a high power, picosecond pulse source at 530 nm pumped by an all-fiber, single mode,
single polarisation, Yb-doped MOPA. The pump MOPA comprised of a gain switched seed source generating 20 ps
pulse source at a repetition frequency of 910 MHz followed by three amplification stages. Output power in excess of 100
W was obtained at 85% slope efficiency with respect to launched pump power at 975 nm. A 15mm long LBO crystal
was used to frequency double the single mode, single polarisation output of the fiber MOPA. To satisfy the phase
matching condition, the internal temperature of the LBO crystal was maintained at 1550C. Frequency doubled power in
excess of 55 W was obtained at 56% optical-to-optical conversion efficiency. Output power at 530 nm started to roll-off
after 50 W due to self-phase modulation (SPM) assisted spectral broadening of the fundamental light within the final
stage amplifier. Measured spectral bandwidth of the frequency doubled signal remained at ~0.4 nm with the increase in
fundamental power even though that of the fundamental increased steadily with output power and reached to a value of
0.9 nm at 100 W output power.
Here we report a high power, pulsed optical parametric oscillator (OPO) at 3.5 μm by using a MgO:PPLN crystal as the
gain medium. The OPO itself was pumped by a semiconductor diode-seeded, Yb3+-doped fiber Master Oscillator Power
Amplifier (MOPA) operating at 1062nm. An OPO output power as high as 11W at an overall slope efficiency of 67%
was achieved, with nearly 2.7W and 8.2W of optical power obtained at 3.5μm and 1.5μm respectively. Due to the fast
response time of the external modulator, it is possible to implement active pulse shaping on a nanosecond time-scale.
Using adaptive pulse shaping of the seed laser (using an external modulator) we demonstrated a reduction in the impact
of dynamic gain saturation and optical Kerr/Raman nonlinearities within the fibre MOPA obtaining shaped signal and
idler pulses at the OPO output and reduced spectral bandwidths. We have also investigated the dependence of the OPO
build-up time and energy transfer efficiency on pump pulse peak power and shape. The build-up time shows an
exponential dependence on the pulse peak power and as expected decreases with an increase in pulse peak power.
Analyzing the shift in spectral peak at 1.5μm it is possible to estimate the internal temperature of the crystal for various
pump powers. Our experiments were pump-power limited and considerable scope remains for further power-scaling of
the OPO output using this approach.
A Fourier transform spectrometer with heterodyne modulation using a moving diffraction grating has been developed for the NIR region. The grating simultaneously acts as a beam splitter and a modulator, which realizes optical frequency shift of incident light for increasing the sensitivity of measurement by heterodyne modulation technique. The difference of diffraction angle is compensated by a collimating lens or a mirror and plane mirrors.
A kind of bireflectance thin film on the window plate of a 633nm He-Ne laser is presented in this paper. The film of non quarter-wave-stack is coated on the substrate with the application of external load on it. The load on the substrate is removed after the coating has been accomplished, then the strain on the substrate will transfer to the multilayer film. Due to photoelastic effect, the multilayer film becomes an anisotropic film. Selecting appropriate film structure and suitable center wavelength, a high phase dispersion with a nearly constant reflectivity will be obtained around the working wavelength. For normal incidence, a phase shift difference between the two orthogonal polarization states of the reflected wave will produce. As a result, a dual-frequency laser with a beat frequency of 4-5 megahertz can be carried out by using this kind of bireflectance thin film. Based on this principle, a He-Ne dual-frequency laser equipped with bireflectance cavity mirror is described. The model coupling is reduced by utilizing transverse Zeeman effect so that two linear and orthogonal polarization components with 5MHz beat frequency are generated. The effect of the magnetic field's direction on the dual-frequency as well as the polarization property of the laser are investigated by experiments. After stabilizing the frequency, the laser is calibrated with the iodine frequency stabilization laser at Chinese National Institute of Metrology. Experimental results indicate that the expanded uncertainty of wavelength in vacuum is 1 X 10-7 with the frequency stabilization of 6.6 X 10-10.
A precision positioning system with a high displacement resolution has been widely required for modern industrialized applications, such as microelectronics, super-precision manufacturing etc. This paper discusses the design and the features of a new piezo driven precision micro positioning stage utilizing flexure hinges. Theoretical analysis for the stiffness of the flexure hinge is also given briefly. A piezoelectric ceramic is applied to drive the precision state, whose displacement can reach 5 micrometers when employed with 1000 voltage power. In order to testify the robust and measurement stability of the precision sta, three kinds of PZT produced in Germany, Japan and China respectively are utilized. A dual-frequency interferometer with nanometer resolution and accuracy is adopted to evaluate the mechanical characteristics of the positioning stage. The experimental result shows that the open loop control of the stage provides 0.2nm positioning resolution along the moving direction.
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