Jaeryung Yoo

Carbon nanotube electron emitters with a gated structure using backside exposure processes

We have fabricated fully vacuum-sealed 5 in. diagonal carbon nanotube field-emission displays of a gated structure with reliable electron emission characteristics. Single-walled carbon nanotube tips were implemented into the gate structure using self-aligned backside exposure of photosensitive carbon nanotube paste. An onset gate electrode voltage for emission was about 60 V and the luminance as high as 510 cd/m2 was exhibited under an application of 100 V and 1.5 kV to gate electrode and anode, respectively.

End-pumped green and blue vertical external cavity surface emitting laser devices

The authors report on the development and demonstration of the high power operation of optically end-pumped vertical external cavity surface emitting laser devices emitting at 532 and 460nm. 2.7W green and 1.4W blue output powers were achieved with a good beam quality by intracavity frequency doubling with second harmonic generation crystal. High efficiency and good beam quality are attributed to the enhanced thermal management by the diamond heat spreader directly bonded to the gain region and effective optical pumping by placing the pump laser diode behind the laser structure.

Efficient blue lasers based on gain structure optimizing of vertical-external-cavity surface-emitting laser with second harmonic generation

We report on the demonstration of highly efficient blue lasers based on intracavity frequency doubling vertical-external-cavity surface-emitting lasers (VECSELs). By optimizing the number of InGaAs quantum wells and employing Al0.3Ga0.7As carrier blocking layers in resonant periodic gain structures, we observed the pump-power-limited output power of 4.5W at 920nm for an InGaAs∕GaAs quantum well VECSEL. With a frequency doubling LiB3O5 crystal inside the cavity, 1.9W continuous-wave 460nm blue output was demonstrated. Power conversion efficiencies (=output power∕pump input power) of 22.5% and 9.5% are realized for λ∼920nm and λ∼460nm, respectively.

920-nm Vertical-External-Cavity Surface-Emitting Lasers With a Slope Efficiency of 58% at Room Temperature

We report a high-power fundamental transverse mode operation of an optically pumped 920-nm vertical-external- cavity surface-emitting laser. The effects of the gain related structural parameters on the laser performance are investigated. Based on the optimization of the gain structure and the thermal management, a maximum pump-limited output power of 12 W in a TEM00 mode with a slope efficiency of 58% (input power of 24 W) was achieved at room temperature.

Enhancement of Pumping Efficiency in a Vertical-External-Cavity Surface-Emitting Laser

We report an improved optical pumping efficiency in a vertical-external-cavity surface-emitting laser (VECSEL) by employing the double-band mirror (DBM), which acts as a pump beam reflector as well as a cavity mirror. The optical pumping efficiency of a VECSEL with the DBM was increased by 23%, as compared to one with the conventional distributed Bragg reflector. It was found that the use of the DBM was more effective in the VECSEL with the shorter absorption layer thickness.

A Measurement of Modal Gain Profile and Its Effect on the Lasing Performance in Vertical-External-Cavity Surface-Emitting Lasers

We investigate the effect of relative wavelength difference between material gain and resonance peaks on lasing performance in vertical-external-cavity surface-emitting lasers (VECSELs). We propose a measurement method of the wavelength-dependent modal gain profiles by inserting a birefringent filter inside a cavity in order to modulate the optical loss according to the wavelength. With knowledge of the detailed gain profiles, we achieve a stable green output power of 3.3 W and a power conversion efficiency (= green output power/pump input power) of 17% in VECSEL with a LiB3O5 crystal as an intracavity frequency doubler

Gain structure optimization of vertical external cavity surface emitting laser at 920nm

The authors have optimized a resonant gain structure of a 920nm vertical external cavity surface emitting laser. They found that long saturated carrier lifetime in shallow quantum well (QW) under a high injection level restricted the laser performance. An insertion of nonabsorbing layer in the middle of barrier layers with multi-QWs was very effective to reduce the saturated carrier lifetime and, therefore, to enhance the laser performance. With the optimized gain structure, which had ten periods of triple InGaAs QWs with Al0.3Ga0.7As nonabsorbing layers in the middle of GaAs barriers, they achieved 4.9W output power at 10°C.

Compact and Efficient Green VECSEL Based on Novel Optical End-Pumping Scheme

We propose a novel lens-less optical end-pumping scheme and report on the development of a highly efficient and compact green vertical-external-cavity surface-emitting laser (VECSEL). A constant-wave pump-power-limited maximum green output power of 1.1 W and an optical-to-optical conversion efficiency of as high as ~15.7% (=1.1 W/7 W) were achieved using a single chip pump laser diode placed directly behind the VECSEL structure without any beam focusing and shaping optical elements.

Effect of the properties of an intracavity heat spreader on second harmonic generation in vertical-external-cavity surface-emitting laser

We investigate the effect of the properties of an intracavity diamond heat spreader on the lasing performance of vertical-external-cavity surface-emitting lasers. We compared two intracavity diamonds with different average birefringences. When a polarization selective element is inserted into the cavity, the infrared output powers are reduced by 13% and 7%, respectively, for the samples with higher and lower average birefringences. The pump-power limited maximum green output powers were changed from 3to5.2W by rotating the samples with lower average birefringence. In order to explain the variation in green output power, the additional round-trip loss caused by diamond birefringence was analyzed theoretically and experimentally. We found that the loss can be reduced when axes of the birefringence are aligned to the axes of the polarization selective element.

2 W continuous wave operation of optically pumped blue VECSEL with frequency doubling

We have optimized a resonant gain structure of a 920 nm vertical external cavity surface emitting laser. We found that a long saturated carrier lifetime in shallow quantum well (QW) under a high injection level restricts the laser performance. An insertion of non-absorbing laser in the middle of barrier layers with multi QWs is effective to reduce the saturated carrier lifetime and, therefore, to enhance the laser performance. With the optimized laser structure, which has 10 periods of triple In0.09Ga0.91 As QWs located at the anti-standing wave optical field with Al0.3Ga0.7As non-absorbing layers in the middle of GaAs barrier, we achieved 4.9 W operation at 920nm. Subsequently blue laser was achieved by employing an intra-cavity frequency doubling crystal LBO. As a result, we demonstrated 2 W single transverse mode operation in blue (460 nm) with a 20 W pump laser power. The conversion efficiency from 808 nm pump laser to the blue laser is measured to be 10 %.