Solid-State Lasers Pumped by LED

Abstract

Light emitting d iode (LED) pumped solid-state lasers were designed. Several solid state materials such as Nd:YA G, Nd :glass, Ti:sapphire, and solid dye were studied. To pump efficiently with LEDs, various types of reflectors were tested. Absorption of rays from arrays of LEDs by solid gain med iu m was calculated and then the calculated data was transferred to co mmercial cavity analysis software. The lasing characteristics such as lasing thresholds, thermal lens, and slope efficiencies were estimated. Introducti onSolid State lasers have been pumped by flash lamps, laser d iode, or other lasers. There are large heat generation and short life time problems when pumped with flash lamps. Laser diode is expensive and it should be protected from humidity, static electricity and dust. These problems have been addressed numerous times over the past decades. In this work, an alternative pump source light emitting diode (LED) was considered. The LEDs were suggested as pump source about 40 years ago. At that time, LEDs had low electric to optical power conversion efficiency [ 1,2] and to obtain laser light, several experimental technics were tried [1][2][3][4]. However, due to low output power of LEDs, the study using LEDs had been rare. Recently, LEDs wh ich have high power output are developed rapidly. Also it has low cost. LED application such as pumping laser is considered here [5]. Calculation and ResultFor the LED pu mped solid-state laser design, we used commercial ray tracing software (ZEMAX) and laser cavity analysis software (LASCA D). The co mbined calcu lation of the software enabled to us to evaluate numerically the laser output performance, totally absorbed LED beam, and the absorbed energy profile inside laser crystal. In the calculation, Nd:YA G, Nd:Glass, solid dye, and Ti:Sapphire solid rods were considered as LED pumped gain media. For precise calculat ion, experimentally measured output power and wavelength of the wh ite and the blue LEDs, which were co mmercially available (S42180 and B42180, Seoul semiconductor), were considered. The output powers were 0.31 W fo r the wh ite LED and 0.46 W for the blue LED. Figure 1 shows the picture of devised LED pumped laser. To pu mp laser crystal efficiently, four LED bars surrounded laser crystal symmetrically. In ZEMAX code, the absorbed LED power inside laser crystal was calculated with help of measured relative strength of emitted spectra fro m LEDs. The absorbed LED power was calculated and it was imported to LASCAD for analysis of thermal effect and laser output power. Figure 2(a) and 2(b ) show the calculated output powers as a function of absorbed white and blue LED power. The optimal output coupler reflectivity was optimized fo r each laser crystal and cavity loss was set as 0.02. We assumed the total maximu m LED output power of 200 W. Fro m the calculation, the absorption efficiency of Nd:YA G, solid dye, Nd :Glass and Ti:Sapphire were 6%, 24% 8%OSA/ SumSession 2011 Tu40-1