YAG Double-clad Crystal Fiber Research Articles

Efficient and low-threshold Cr^4+:YAGdouble-clad crystal fiber laser

A significant advancement of cw lasing in Cr4+:Y3Al5O12 (Cr4+:YAG) double-clad crystal fiber grown by the codrawing laser-heated pedestal growth technique was demonstrated at RT. The optical-to-optical slope efficiency of 33.9% is the highest, to the best of our knowledge, among all Cr4+:YAG lasers, whether they are in bulk or fiber forms. The low-threshold lasing of 78.2 mW and high efficiency are in good agreement with the simulation. The keys to the high laser efficiency are twofold: one is the improved Cr4+ emission cross section and fluorescence lifetime due to release of the strain on the distorted Cr4+ tetrahedron, which also mitigates photobleaching in Cr4+:YAG; the other is the improved core uniformity at long fiber lengths. In addition, because of the low threshold, the impact of excited state absorption of the pump light is significantly reduced. The effects of crystal-orientation, self-selected, and pump-dependent linear polarization states were also addressed.

Bidirectionally pumped Cr^4+:YAG crystal fiber light source for optical coherence tomography

A broadband Cr4+:YAG double-clad crystal fiber light source with a collimated output power of 3.15mW was demonstrated by using a bidirectional pump scheme. The bidirectional pump scheme increased the pumping efficiency and reduced the thermal problem along the fiber. Good agreement on the output power of the broadband fluorescence was achieved between experiment and theory, which showed a peak net gain coefficient of 0.03cm−1 at the center wavelength near 1380nm. The 3dB bandwidth of 222nm with a Gaussian-like spectrum makes it eminently suitable for broadband interferometric technique to have low image cross talk. The calculated interference signal shows a 3dB width of 3.62μm with a cross talk smaller than −24dB for adjacent axial image pixels.

High-Luminance White-Light Point Source Using Ce,Sm : YAG Double-Clad Crystal Fiber

Ce and Sm ions codoped yttrium aluminum garnet (Ce,Sm : YAG) double-clad crystal fibers (DCFs) were successfully fabricated using the codrawing laser-heated pedestal growth method. At a pump wavelength of 446 nm, white-light point source was produced from a 10--core DCF. The amplified spontaneous emissions and the residual pump resulted in a directional high brightness point source. A luminance of 4.5 × 109 cd/m2 was generated. The luminous flux of the point white light was 6.2 lm. When coupled to a 200-core multimode fiber, the output power and coupling efficiency were 4.8 mW and 36.8%, respectively. Point white-light sources are useful for biomedical endoscopic application and long-range directive illumination. The generated broadband yellow emission can also be served as the light source for optical coherence tomography system. Using the 91-nm yellow emission, an axial resolution of 1.5-optical coherence tomography can be achieved for ultrahigh-resolution ocular and industrial applications.

Ce^3+:YAG double-clad crystal-fiber-based optical coherence tomography on fish cornea

A Ce(3+):YAG double-clad crystal fiber (DCF) visible emission was used as the light source for optical coherence tomography (OCT). The visible emission was produced from a 10 microm core DCF pumped by a diode laser. The broadband emission and short central wavelength of this light source enabled the realization of 1.5 microm axial resolution in air. The relatively clean spectrum reduced the side lobe of its point-spread function, and therefore facilitated the generation of a high-quality image with less crosstalk between adjacent image pixels. As a demonstration, an Aplocheilus lineatus goldfish was experimented on to map out the stroma of its cornea. This visible-light-based OCT can be utilized for industrial inspection as well as ocular applications.

Cr^4+:YAG double-clad crystal fiber laser

We report what we believe to be the first demonstration of a room-temperature, continuous-wave Cr(4+):Y(3)Al(5)O(12) (Cr(4+):YAG) double-clad crystal fiber laser grown by the codrawing laser heated pedestal growth method. The threshold is below 100 mW, which is a factor of 4 lower than previously reported Cr(4+)-doped lasers. A slope efficiency of 6.9% was obtained, and is in good agreement with the numerical simulation. In additional to small core diameter, the low-threshold lasing is made possible by the low propagation loss of 0.08 dB/cm and the high crystallinity of the core.

Low-loss propagation in Cr^4+:YAG double-clad crystal fiber fabricated by sapphire tube assisted CDLHPG technique

Cr4+:YAG double-clad crystal fiber with an uniform 10-microm core was fabricated by using a sapphire tube as a heat capacitor to stabilize the power fluctuation of the CO2 laser in the co-drawing laser-heated pedestal growth system. The uniformity of the fiber core showed a factor of 3 improvement compared to that without the use of sapphire tube. The variation of the core diameter is within the +/-1.35-degree adiabatic criterion and has a autocorrelation length of 1.7 mm. The measured propagation loss is only 0.02 dB/cm. The sapphire tube also reduces the vertical temperature gradient during the crystal fiber growth process so the 10-microm crystal core exhibits a smooth perimeter. The sapphire tube assisted system can be applied to the growth of many other optical crystal materials.