High power 808 nm vertical-cavity surface-emitting laser (VCSEL) arrays were used to end-pump diffusion-bonded composite laser rods consisting of an Nd:YAG gain medium and a Cr:YAG saturable absorber. The laser pulse energy, q-switch delay time, and optical efficiency of a passively Q-switched monolithic solid state laser in a compact rugged package were measured as a function of VCSEL power for various heatsink temperatures. Up to 19 mJ laser pulse energy was produced with 13% optical efficiency.
KEYWORDS: Vertical cavity surface emitting lasers, Mobile devices, Gesture recognition, Three dimensional sensing, 3D surface sensing, 3D image capture, Optical filters, Laser sources, Structured light, High power diode lasers, Time of flight imaging, Diffusers, Temperature metrology, Reliability, Infrared imaging, Stereoscopy
There has been increased interest in vertical-cavity surface-emitting lasers (VCSELs) for illumination and sensing in the consumer market, especially for 3D sensing ("gesture recognition") and 3D image capture. For these applications, the typical wavelength range of interest is 830~950nm and power levels vary from a few milli-Watts to several Watts. The devices are operated in short pulse mode (a few nano-seconds) with fast rise and fall times for time-of-flight applications (ToF), or in CW/quasi-CW for structured light applications. In VCSELs, the narrow spectrum and its low temperature dependence allows the use of narrower filters and therefore better signal-to-noise performance, especially for outdoor applications. In portable devices (mobile devices, wearable devices, laptops etc.) the size of the illumination module (VCSEL and optics) is a primary consideration. VCSELs offer a unique benefit compared to other laser sources in that they are "surface-mountable" and can be easily integrated along with other electronics components on a printed circuit board (PCB). A critical concern is the power-conversion efficiency (PCE) of the illumination source operating at high temperatures (>50 deg C). We report on various VCSEL based devices and diffuser-integrated modules with high efficiency at high temperatures. Over 40% PCE was achieved in broad temperature range of 0-70 °C for either low power single devices or high power VCSEL arrays, with sub- nano-second rise and fall time. These high power VCSEL arrays show excellent reliability, with extracted mean-time-to-failure (MTTF) of over 500 years at 60 °C ambient temperature and 8W peak output.
Vertical-cavity surface-emitting lasers (VCSELs) are attractive for many pumping and direct-diode applications due to combined advantages in low cost, high reliability, narrow and thermally stable spectrum, high power scalability, and easy system integration, etc. We report our progress on electrically pumped, GaAs-based, high- power high-brightness VCSELs and 2D arrays in the infrared wavelength range. At 976nm, over 5.5W peak CW output and 60% peak power conversion efficiency (PCE) were demonstrated with 225um oxide-confined device. For 5x5mm arrays, peak PCE of 54% and peak power of >450W at 976nm, peak PCE of 46% and peak power of >110W at 808nm were achieved respectively under QCW conditions. External cavity configuration was used to improve the VCSEL brightness. Single mode output of 280mW and 37% PCE were realized from 80um device. For large 325um device, we obtained single mode (M2=1.1) CW output of 2.1W, corresponding to a brightness of 160MW/cm2*sr. Three major areas of applications using such VCSELs are discussed: 1. High brightness fiber output; 2. High power, high efficiency green lasers from 2nd harmonic generation. 3.34W green output with 21.2% PCE were achieved; 3. Pumping solid state lasers for high energy pulse generation. We have demonstrated Q-switched pulses with 16.1mJ at 1064nm and 4.9mJ with 1W average power at 473nm.
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.
A compact UV pulsed laser pumped by high-power two-dimensional arrays of vertical-cavity surface-emitting lasers
(VCSELs) was presented. A passively Q-switched 1064-nm Nd:YAG laser was side-pumped by kW-class 808-nm VCSEL pump modules and the output pulses were frequency quadrupled to 266-nm. 10-ns, 0.68-mJ UV pulsed output was obtained at 1.33k-Hz repetition rate. The average UV power is < 0.9-W. This VCSEL pumped high power UV laser source provides a reliable, low-cost and low-profile solution for military and commercial applications including remote
sensing, laser processing and spectroscopy.
We present thermally regnenerated fiber Bragg grating in air-hole microstructured fibers for high temperature hydrostatic
pressure sensing application. Saturated type I gratings were inscribed in hydrogen-loaded two-hole optical fibers using
248-nm KrF laser, and regenerated during annealing at 800ºC. The fiber Bragg grating resonance wavelength shift and
peak splits were studied as a function of external hydrostatic pressure from 15 psi to 2400 psi. The grating pressure
sensor shows stable and reproducible operation up to 800ºC. This paper demonstrates a multiplexible pressure sensor
network technology for high temperature harsh environment using a single fiber feedthrough.
This paper presents simulation and experimental results of orientation-dependent transverse load fiber sensors using fiber
Bragg gratings written in four-hole suspended core fibers. Resonant peak shifts and splitting of fiber Bragg gratings were
studied as functions of the applied transverse load and its orientation. Both simulation and experimental results revealed
that response of fiber Bragg grating in suspended core fibers are sensitive to both orientation and magnitude of transverse
strains.
Cryogenic fuels are often considered as major energy alternatives to coal and petroleum based fuels. Safe and reliable
sensor networks are required for on-demand, real-time fuel management in cryogenic environments. In this paper, a new
sensor design is described that enhances the low-temperature performance of fiber sensors. FBGs inscribed in high
attenuation fiber (HAF) are used to absorb in-fiber power light to raise the local sensor temperature in the cryogenic
environment. When in-fiber power light is turned off, FBG sensors can serve as passive sensors to gauge temperature
and stress in the cryogenic system. When the in-fiber power light is turned on, the heated sensors can be used to rapidly
gauge fuel level and fuel leaks. In one example, a hydrogen gas sensor is demonstrated with a palladium-coated fiber
Bragg grating (FBG). The low-temperature performance of the sensor was improved by heating the gratings as much as
200 K above the ambient temperature, and hydrogen concentration well below the 4% explosion limit was measured at
123K. In a second example, an array of four aluminum coated fiber Bragg gratings was used to measure liquid level in a
cryogenic environment.
We report an all-fiber hydrogen sensing system for low-temperature operation. The sensor consists of a fiber Bragg
grating written in high-attenuation fiber and coated in Palladium. Heating the sensor with in-fiber light power greatly
enhances sensitivity at low temperatures. A multi-functional infrared light source is used to provide both in-fiber heating
and sensor monitoring. This technology promises a single fiber feedthrough solution for low temperature multipoint
hydrogen leak detection.
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