We are developing VCSEL technology producing >100mW in single frequency at wavelengths 780nm, 795nm and 850nm. Small aperture VCSELs with few mW output have found major applications in atomic clock experiments. Using an external cavity three-mirror configuration we have been able to operate larger aperture VCSELs and obtain >70mW power in single frequency operation.
The VCSEL has been mounted in a fiber pigtailed package with the external mirror mounted on a shear piezo. The package incorporates a miniature Rb cell locker to lock the VCSEL wavelength. This VCSEL operates in single frequency and is tuned by a combination of piezo actuator, temperature and current. Mode-hop free tuning over >30GHz frequency span is obtained. The VCSEL has been locked to the Rb D2 line and feedback control used to obtain line-widths of <100kHz.
We have achieved a 21.2% wall-plug efficiency green laser at 532 nm based on an electrically pumped vertical externalcavity surface emitting laser (VECSEL) through intracavity second harmonic generation. The continuous-wave green output power was 3.34 W. The VECSEL gain device is cooled by using a thermoelectric cooler, which can greatly benefit packaging. Both power and efficiency can be further scaled up by optimizing external-cavity design and improving the performance of VECSEL gain device.
We report on a Q-switched VCSEL side-pumped 946 nm Nd:YAG laser that produces high average power blue light with high pulse energy after frequency doubling in BBO. The gain medium was water cooled and symmetrically pumped by three 1 kW 808 nm VCSEL pump modules. More than 1 W blue output was achieved at 210 Hz with 4.9 mJ pulse energy and at 340 Hz with 3.2 mJ pulse energy, with 42% and 36% second harmonic conversion efficiency respectively. Higher pulse energy was obtained at lower repetition frequencies, up to 9.3 mJ at 70 Hz with 52% conversion efficiency.
High power, kW-class, 808 nm pump modules based on the vertical-cavity surface-emitting laser (VCSEL) technology were developed for side-pumping of solid-state lasers. Two 1.2 kW VCSEL pump modules were implemented in a dual side-pumped Q-switched Nd:YAG laser operating at 946 nm. The laser output was frequency doubled in a BBO crystal to produce pulsed blue light. With 125 μs pump pulses at a 300 Hz repetition rate 6.1 W QCW 946 nm laser power was produced. The laser power was limited by thermal lensing in the Nd:YAG rod.
Solid-state lasers pumped by high-power two-dimensional arrays of vertical-cavity surface-emitting lasers (VCSELs)
were investigated. Both end-pumping and side-pumping schemes of Nd:YAG lasers with high power kW-class 808 nm
VCSEL pump modules were implemented. For one application 10 mJ blue laser pulses were obtained from a frequencydoubled
actively Q-switched VCSEL-array dual side-pumped Nd:YAG laser operating at 946 nm. For another
application 10 mJ green laser pulses were obtained from a frequency-doubled passively Q-switched VCSEL-array endpumped
Nd:YAG laser operating at 1064 nm. Both QCW and CW pumping schemes were investigated to achieve high
average Q-switched power.
High power 808 nm VCSEL arrays were developed to pump compact pulsed Nd:YAG lasers. A QCW side-pumped
passively Q-switched Nd:YAG laser operating at 1064 nm produced linearly polarized 4 ns IR pulses with 4.7 mJ pulse
energy. These pulses were externally frequency doubled and quadrupled resulting in 2.5 mJ pulse energy at 532 nm and
0.8 mJ at 266 nm respectively. A similar but actively Q-switched dual side-pumped Nd:YAG laser operating at the
weaker quasi three-level 946 nm transition produced 12 mJ pulses that were efficiently frequency doubled resulting in
5.6 mJ blue pulses of 17 ns duration.
We are developing a low noise high power ultra-stable diode pumped Er-Yb co-doped phosphate glass
laser. Erbium doped phosphate glass permits high co-doping with ytterbium ions that strongly absorb at
976 nm and efficiently transfer their energy to the active erbium material. This drastically decreases the
absorption length at the 976 nm pump wavelength and thus the overall size of the laser. Aside from the
advantage for packaging a short cavity length results in a large longitudinal mode-spacing (>40 GHz),
which allows for single longitudinal mode operation in the 1530-1565 nm C-band for telecommunication
by inserting a tunable low-finesse etalon in the laser cavity. In addition, due to the energy transfer between
the co-dopant and the active material, the laser shows a strongly reduced sensitivity to fluctuations in pump
power. The strong peak in the RIN spectrum at the relaxation oscillation frequency (0.1-1 MHz) due to
cavity-loss perturbations can be drastically reduced with a non-linear absorbing material inside the laser
cavity. Using this approach for an optimized laser cavity design we have achieved -160 dB/Hz RIN at 1
MHz for 35 mW output. Above 100 MHz the RIN becomes shot noise limited (-168 dB/Hz @ 20mA
photocurrent). The laser has excellent long-term frequency stability when locked to our wavelength locker
(<250 kHz). Furthermore, the laser has been shown to have a narrow intrinsic linewidth (~10 Hz) that we
are working towards by means of intra-cavity phase modulation.
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