Highly brilliant diode lasers at 1120nm with a high optical output power, nearly diffraction limited beam and narrow spectral line width are increasingly important for non-linear frequency conversion to 560 nm. We present experimental results about edge-emitting distributed Bragg reflector (DBR) tapered diode lasers emitting at 1120 nm. The investigated lasers show an output power of up to 8W with a conversion efficiency of about 40%, and a lifetime of more than 5000 h at 5 W. The lasers also exhibit a small vertical divergence <15° full width at half maximum (FWHM), a nearly diffraction limited beam quality, and a narrow spectral line width with FWHM smaller than 10pm. These properties allow the lasers to be used for future second harmonic (SH) generation.
To create holographic or volumetric displays, it is highly desirable to move from conventional imaging projection
displays, where the light is filtered from a constant source towards flying spot, where the correct amount of light is
generated for every pixel. The only light sources available for such an approach, which requires visible, high output
power with a spatial resolution beyond conventional lamps, are lasers. When adding the market demands for high
electro-optical conversion efficiency, direct electrical modulation capability, compactness, reliability and massproduction
compliance, this leaves only semiconductor diode lasers.
We present red-emitting tapered diode lasers (TPL) emitting a powerful, visible, nearly diffraction limited beam (M²1/e² <
1.5) and a single longitudinal mode, which are well suited for 3d holographic and volumetric imaging. The TPLs
achieved an optical output power in excess of 500 mW in the wavelength range between 633 nm and 638 nm. The
simultaneous inclusion of a distributed Bragg reflector (DBR) surface grating provides wavelength selectivity and hence
a spectral purity with a width Δλ < 5 pm.
These properties allow dense spectral multiplexing to achieve output powers of several watts, which would be required
for 3d volumetric display applications.
We demonstrate a compact high-power green (532nm) laser module based on single-pass second harmonic generation.
The pump source is a distributed Bragg reflector tapered diode laser. The frequency conversion is achieved with a 2.5 cm
long periodically poled MgO:LiNbO3 bulk crystal. The entire module is integrated on a compact micro-optical bench
with a footprint of 2.5 cm3. Up to 1.1 W output green light power is achieved at a pump power of 7.6 W with an optical
conversion efficiency of about 15% and a corresponding module wall-plug efficiency of more than 4%. The green laser
beam has a relatively good beam quality (measured at output power level of ~0.9 W) with M²σ=1.8 in the vertical
direction and M²=4.9 in the lateral direction, respectively. The long-term output power stability is ±10% (tested at
output power level of ~0.6 W).
Recently, hybrid integrated compact laser sources with high optical output powers in the visible range around 488 nm
were demonstrated using tapered diode lasers. This was done by single-pass second harmonic generation (SHG) using a
periodically poled LiNbO3 crystal of 30 mm length. The conversion efficiency depends on the light source but is also a
function of the temperature distribution along the length of the crystal.
The maximum conversion efficiency of a given beam is theoretically achieved by a homogenous temperature
distribution. Experiments have shown that for high power SHG different absorption mechanisms are causing a
temperature gradient in the crystal. This gradient leads to an inhomogeneous poling period, which diminishes the
effective crystal length and leads to a smaller conversion efficiency.
In this paper we present a method for the optimization of the temperature management during the SHG. This is done by a
multizone heater package that can be integrated into compact laser sources. This package can be used to create arbitrary
temperature distributions and is especially able to compensate an arising temperature gradient.
We demonstrate monolithic distributed-Bragg-reflector tapered diode lasers having an output power up to 12 W, a small
spectral width of below ▵λ<10 pm and a beam quality close to the diffraction limit. This results in a brightness close to
1 GWcm-2sr-1. Due to these excellent electro-optical characteristics we achieved visible laser light up to P=1.8 W in a
single-path second harmonic generation experiment. This allowed us to develop compact Watt-class (P=1.1 W) visible
laser modules having an excellent beam quality (M²<3) with a narrow spectrum (▵λ<30 pm). The entire device is
integrated on a micro-optical bench with a volume below 20 cm³. In another application we demonstrate for the first time
a femtosecond gigahertz SESAM-modelocked Yb:KGW laser. Such a laser system benefits from the small spectral
emission and the focusability of the developed diode laser. A record peak power of 3.9 kW was achived. At the
repetition rate of 1 GHz, 281 fs pulses with an average output power of 1.1 W were generated. This Yb:KGW laser has a
high potential for stable frequency comb generation.
In this paper, we utilize the concept of the Wigner distribution function (WDF) on distributed-Bragg-reflector taper
lasers (DBR-TPL). The WDF allows the derivation of the phase and the intensity distribution just as well as the spatial
coherence properties of the laser beam. For a given single-mode fiber the coupling efficiency for a given beam and
optical system can be obtained by means of a simple overlap integral. Simultaneously, this approach delivers the
corresponding beam forming requirements to meet the optimum coupling condition. We found a good agreement
between the measured coupling efficiencies of the DBR-TPL into a single-mode fiber under varying coupling conditions
and the corresponding efficiencies derived from the measured WDF by simulating the same coupling conditions.
We demonstrate a compact 1 W laser module at 490 nm using a Distributed Bragg Reflector tapered diode laser in
single-path second harmonic generation (SHG) configuration. The frequency conversion is performed with a 3 cm
periodically poled MgO:LiNbO3 crystal on a micro-optical bench having a footprint of 2.5 cm3. 1 W blue light could be
achieved at a pump power of about 9.5 W resulting in an optical conversion efficiency of about 10 %. The output power
stability is better than ± 2% and the blue laser beam shows an excellent beam quality of M2σ = 1.2 in vertical and M2σ = 2
in lateral direction, respectively.
Compact laser light sources in the visible spectral range emitting several Watts are required for display
technology, sensor systems and material processing. Second harmonic generation (SHG) using highly brilliant edge
emitting infrared lasers is a promising way to fill the spectral gap of directly emitting semiconductor lasers. Newly
developed distributed Bragg reflector (DBR) tapered lasers allow a very efficient SHG due to their extraordinary
brightness. On an optical bench more than 1 W power at 488 nm was obtained by directly doubling the laser light with
a 5 cm long PPLN crystal. Using hybrid integration on a micro-optical benches we now achieved 0.5 W power at 488
nm with a 2.2 cm long PPLN crystal.
In this paper we present a study of the single pass normalized second harmonic generation (SHG) conversion
efficiency as a function of the beam propagation factor M2 and the beam diameter in the lateral and vertical
direction. It can be shown that an increase in M2 results in dramatic changes for the optimal focusing conditions,
in comparison to the SHG with a Gaussian beam. Based on the results of the measurements we developed a
model to simulate the focusing conditions for partial coherent beams.
For the pumping of solid state lasers with high peak power pulses up to the TW range QCW diode laser stacks with pulse
lengths between 200μs and 2ms are used. To realize long-term stable pump modules we already presented high power, high brightness 100W QCW diode laser bars [1] having a lateral aperture of 1.7mm only, a length of 4mm and a vertical divergence of 14° FWHM. Based on these we have developed a mounting scheme for stacks with > 1kW output power using these new kind of diode lasers.
Due to the geometric dimensions of the chip we successfully realized a stack with a passive cooling scheme on both
sides. Furthermore, we only used expansion matched materials such as CuW and Al2O3 ceramics, as well as AuSn
solder processes for fixing the parts together. As a result the stack is very insensitive against environmental influences.
Due to the small vertical divergence we were able to use fast axis collimators with large focal lengths, which relax the
lens adjustment tolerances.
At the conference we will present results for diode laser stacks with an output power of more than 1kW at duty-cycles up
to 10% and an efficiency of about 50%. The beam parameter product for such diode laser stacks result in < 50mm•mrad
for the vertical direction and in < 75mm•mrad for the lateral direction. These beam parameter values enable the coupling
of the pump module to an optical fiber having a 1.2mm core diameter and a NA of 0.22.
Furthermore, the low vertical fill factor of the stack radiation allows the combination of two stacks by beam deflection
mirrors without significantly degrading beam quality, hence doubling the power coupled into the same fiber.
We present a study of the single pass SHG conversion as a function of the Rayleigh length (RL) and beam diameter
(BD) using a monolithic distributed Bragg reflector (DBR) tapered laser. The DBR tapered laser has a 6th order surface
grating and a ridge waveguide. Single longitudinal mode emission at 978nm with a side-mode suppression ratio of
more than 40dB and at an output power of 2.7W at 15°C have been obtained in continuous wave operation. The beam
was collimated using an aspheric and a cylindrical lens and focused using a variety of lenses with various focal lengths.
The resulting caustics were acquired using a camera and used for SHG in a 5cm periodically poled LiNbO3 (PPLN)
crystal. This allowed an investigation of the dependency of the SHG conversion efficiency on the RLs and BDs. We
obtained 330mW of output power at 488nm using the optimal focus length. The experiments showed that an optimum
conversion requires longer focal length's then forecasted by Boyd-Kleinman's theory, which is explained due to the
partial coherence. We developed an extension of that theory to account for that partial coherence, which bases in
principle on a mismatch related general Agrawal's nonlinear integration kernel. We use this theory to explain the
dependence of the SHG efficiency from the beam propagation factor M2.
KEYWORDS: Near field, Semiconductor lasers, Near field optics, High power lasers, Reliability, Waveguides, Modulation, Resistance, Control systems, Surgery
High-power diode lasers operating at 808 nm and consisting of a multiple ridge-waveguide structure have been
fabricated. Lasers with this structure show a more stable far and near field pattern in comparison to conventional single
stripe broad area lasers. A reliable continuous wave operation at room temperature over 8000 h at 8 W and 800 h at 10 W
has been achieved with 200 &mgr;m stripe width devices.
We demonstrate 940nm diode lasers with more than 100W QCW output power having an aperture width 5 to 10 times
smaller than commonly used 10mm bars. We used a super-large vertical waveguide structure to reduce the facet load.
The waveguide design results in a very small vertical divergence of only 14° FWHM (24° including 95% of power). The
threshold current of a device with 1mm wide aperture is about 8A and the slope efficiency is above 70%. The lateral far
field width is below 10°, including 95% of power, and the wall plug efficiency is around 50% at 100W output power.
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