This PDF file contains the front matter associated with SPIE Proceedings Volume 12402, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

In this paper we study the pulse quality degradation of an Ytterbium-based fiber laser in which B-integral ranges from 5 to 20 rad. A tunable chirped-fiber-Bragg-grating stretcher is optimized in term of reflectivity and phase profiles thank to a multivariable optimization algorithm. Parabolic and Sech² spectral profiles are both studied in order to evaluate their robustness to non-linear degradation. Phase and reflectivity optimization can provide insight to design tailored specific pulse stretchers for CPA systems.

We present the design and performance of novel, highly stable, broadband, packaged single mode Tm-doped and Ho-doped ASE sources in the 2000 nm spectral band. Centroid wavelengths of 1850–1900 nm are achieved for Tm-doped sources and ~2070 nm for Ho-doped sources. Measured -10 dB spectral bandwidths exceed 100 nm for the Tm-doped sources and 60 nm for the Ho-doped sources. Output powers for two stage Tm-doped sources exceed 1 W CW.

We report the latest development of a polarization-maintained fiber-coupled miniaturized external cavity diode laser (ECDL) at 780 nm with a narrow linewidth of less than 100 kHz and optical isolation of higher than 60 dB integrated into a temperature controlled hermetically sealed industrial standard butterfly package. Combined with a fiber-coupled tapered amplifier, this provides a plug and play low SWaP (Size,Weight and Power consumption) “Master Oscillator Power Amplifier”-system, without the need of additional bulky optical free-space components such as optical faraday isolators and time-consuming optical alignment. In addition to robustness and high stability, we were able to combine the narrow linewidth of the external cavity diode laser and the high output power of the amplifier in the footprint of only two butterfly packages. Output powers higher than 25 mW of the seed laser ex-fiber are sufficient to saturate the tapered amplifier to reach optical powers of more than 3 W with high beam quality and integrated beam collimation. The integrated isolators with isolation greater than 60 dB assure a stable operation and no disturbance of the seed laser by the tapered amplifier. Furthermore, we used an additional optical resonator to reduce the linewidth to less than 10 kHz using an electronic stabilization scheme according to the Pound-Drever-Hall technique with electronics provided by TOPTICA Photonics AG.

For several non-destructive spectroscopy methods based on quantum mechanical effects (e.g. MID-IR quantum-OCT) the size of currently used solid state lasers prevents effective miniaturization. Red-emitting diode lasers with single longitudinal and single lateral mode emission are therefore required for successful out-of-the lab usage. To address this challenge, the FBH developed specialized tapered lasers (TPL) emitting near 660 nm with an integrated tenth order distributed Bragg reflector (DBR) surface grating, requiring only a single epitaxy step. The facets were passivated and coated to obtain reflectivities of 5% for the front and 30% for the rear facet. The DBR-TPL chips were mounted p-side down on CVD-diamonds with structured contacts to allow separate contacting of the ridge waveguide (RW) and tapered (TP) sections. The DBR-TPLs feature a nearly diffraction limited output beam with a spectral width below 0.5 pm, corresponding to a coherence length of almost 1 m. An optical output power of more than 1 W could be demonstrated at currents of 50 mA and 2.5 A for the RW and TP sections, respectively. The beam quality at 1 W was M²_1/e² = 1.1 (M²_4σ = 2.1). The DBR-TPLs are a first important component in the concept for a miniaturized portable quantum-OCT scanner. Here, the sample will be illuminated with MID-IR photons while the entangled NIR photons will be measured with a cost-effective, Si-based spectrometer.

The decrease of transmittance due to electromagnetic radiation is the so-called solarization. This effect is especially well documented for energetic UV light. Typically, these radiations generate color-centers in the glass that act as absorption sites whose spectral characteristic and magnitude depend strongly on the composition. In a recent work, we demonstrated that high power blue laser light, can also lead to solarization of optical glass. In recent years blue laser based solutions (wavelengths around 450 nm) became more and more present in industrial and commercial applications. Blue laser light has in deed unique capabilities for material processing of copper gold or aluminum. Due to their very high power densities modern blue laser diodes are also a technology of choice for illumination system of high performance digital projection, e.g. for cinema and event applications. Optical glasses are widely used in optical systems of blue light laser applications. From now on, these glasses must meet the stability requirements challenged by the steadily increasing power of blue laser, de facto understanding and mitigating this solarization phenomena is now a prime technical challenge. However, until recently only limited data were available on the specific solarization behavior of optical glass under high power blue laser radiation. To this end, SCHOTT has established a dedicated laser irradiation setup to thoroughly characterize blue laser solarization effects of optical glass. Strategies have been developed to achieve blue laser solarization stable glass for demanding applications. In the present work, we shows the stability of different optical glasses against blue laser solarization and discusses the results of the stabilization approach. Aspects like saturation level of the effect, power density and wavelength dependence are discussed for N-BK7 as an example.

We report 6 kW pump limited power handling in a 7+1 to 1 Pump-Signal Combiner. The high pump transmission efficiency of 98% and optimal thermal management of the combiner package enables a low thermal slope of 0.0037 C/W measured up to 6 kW of pump power. The low thermal slope allows for a potential 9 kW pump power handling capacity of the 7+1 to 1 combiner.

A rhodium-emitted X-ray with a photon energy at 20 KeV was employed to irradiate CaF₂ with different surface finishing. Color centers associated with the irradiation damage were determined by spectral measurements. The depth distribution of the color centers was calculated and confirmed in a wedge spot generated by magnetorheological finishing. The results suggest that the color center formation is directly associated with the damage resistance of the optics. Laser durable grade CaF₂ demonstrates higher damage resistance to the X-ray irradiation when compared to excimer ArF laser grade CaF₂. Subsurface-damage-free CaF₂ surfaces further enhance the damage resistance.

We show the use of our dot projector technology with a compact module to enable very high performances for consumer, industrial and automotive applications. We demonstrate 5x3 projected pattern of thousands of dots with very high transmission efficiency and uniformity. Thanks to our vertical integration with optical design, Mastering and replication, the thousands of projected dots are showing constant spot pitch, uniform contrast and are highly repeatable for mass-production. These results were achieved with a highly reliable material, passing 1,000 hours of temperature cycling and humidity tests according to the international standard JESD22-A104 and A101, easily scalable to very high volume thanks to nanoimprint lithography process.

Laser material processing applications often require the flat-top beam profile within focal spots ranged below 100 μm. For high power applications, volume phase masks recorded in photo- thermo-refractive glass (PTR) are promising. The problem is how to achieve simultaneously a high-quality shape and a small size of the beam. The commercial phase masks usually show large power losses in the beam wings, only about 40% of the energy was concentrated under the 95% level. By applying a gray phase mask instead of binary mask, one can reduce losses in the wings of the beam. In this work, a spatial light modulator (SLM) with designed computer generated holograms (CGHs) was used as a beam converter. Using the SLM with programmed gray mask allows obtaining flexible laser beam shaping, but beam quality is limited by imposed parameters of the SLM. The requirements for obtaining a square flat-top beam with energy lost in wings less than 10% is described. It was found that for sharp edges of the square flat-top beam, it is necessary that the size of the output beam contains at least 16 pixels of SLM. This fact is a consequence of the Fourier transform, where high spatial frequencies are responsible for the shape. The concept design of the scanning progressive mechanism of the master volume phase mask recording to exclude the influence of SLM work area dimensions is discussed.

With continuously increasing output power of fiber lasers, small volume, lightweight, high electro-optic efficiency fiber laser is needed. The weight of the semiconductor laser accounts for half of the weight of the entire fiber laser. Therefore lower weight high brightness high power diode laser pump source has become the inevitable trend of development. Lightweight need small volume, low density material. Copper and aluminum are commonly used shell materials. Copper has excellent heat dissipation which density is three times that of aluminum. Lightweight need to balance the contradiction between heat dissipation and weight. BWT designed a diode laser pump source which power ratio is 2.3W/g. The shell materials are mainly copper and aluminum. Using spatial beam combination, polarization beam combination, together with 3-dimensional space dense arrangement, lower weight diode was achieved.

On last year’s SPIE conference, BWT has launched a pump source in weight around 500g, which was locked at 976nm, output 420W from a 135μm diameter and NA 0.22 fiber. In order to meet the need of higher output power pumping of fiber lasers, BWT has achieved 650W output from a 135μm diameter and NA0.22 fiber with a diode laser locked at 969nm and 982nm based on dense spatial beam combination (DSBC) and wavelength beam combination. In the absorption spectrum of Yb3+ ions, 969nm and 982nm have lower absorption coefficients than 976nm,. The active fiber with the same doping concentration will produce less heat accumulation per unit length, which has an obvious effect on improving the TMI threshold (transverse mode instability) and increasing the single-mode fiber laser power. With the enhancement of pump source brightness and the improvement of active fiber doping process and wave-guide structure, the power of single mode fiber laser directly pumped by diode laser is expected to exceed 10kW in the future.

By designing a lightweight and compact stacked bar package, we can achieve high-power, high-brightness, and high-stability pulse laser output. The laser diode package consists of eight 1cm high power laser bars, which are bonded between two copper-tungsten heat sinks with AuSn hard solder like a sandwich. These sandwiches are bonded in a second soldering step on a backplane macro-channel cooler. The package structure is very compact and lightweight. We can achieve different frequency, pulse width, duty cycle combinations, which easily allows to adapt to different applications. In this paper, the performance of 808nm and 940nm laser bars is verified under different conditions: The pulse width is varied from 5 to 300ms, and the frequency range is between 1Hz to 10Hz. Resulting duty cycles range from 10% to 40%. In addition this structure can combine two or more wavelengths (808nm and 940nm, 760 and 1060 optional). We achieve 1788W under the condition of 5ms, 10%DC, 200A. This compact and powerful 2D diode laser array with mixed wavelengths is very suitable for laser hair removal. It can not only fully act on the melanin of the hair follicle, but also coagulate the micro vessels around the hair follicle to cut off the blood supply of the hair follicle. With the right combination of wavelength, the penetration depth and absorbtion characteristics can be tailored to the different skin types from white to dark skin, avoiding skin irritation and pain. For pulsed pumping applications or far field illumination, FAC lenses can be applied to allow for best beam brightness. The package can be designed from single bar to 12 bars, depending of the power demand for the individual applications. Dense packaging of more than one stack in one laser unit allows high application power of multiple kW in a compact handpiece design for hair removal.