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.
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 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.
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.
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.