Hao Yin

Passively Q-switched dual-wavelength green laser with an Yb:YAG/Cr^4+:YAG/YAG composite crystal

A compact dual-wavelength passively Q-switched green laser by intra-cavity frequency doubling of a Yb:YAG/Cr4+:YAG/YAG composite crystal was demonstrated for the first time to our best knowledge. The maximum green laser output power of 1.0 W was obtained under the pump power of 9.7 W, and the corresponding slope efficiency is 15.2%. The shortest pulse width, largest pulse energy, and highest peak power were achieved to be 5.54 ns, 246.1μJ, and 40.76 KW, respectively. Dual-wavelength laser oscillation simultaneously at 515 nm and 524.5 nm has been achieved. This passively Q-switched dual-wavelength green laser can be used as a laser source for Terahertz generation.

Identification of cancerous gastric cells based on common features extracted from hyperspectral microscopic images.

We construct a microscopic hyperspectral imaging system to distinguish between normal and cancerous gastric cells. We study common transmission-spectra features that only emerge when the samples are dyed with hematoxylin and eosin (H&E) stain. Subsequently, we classify the obtained visible-range transmission spectra of the samples into three zones. Distinct features are observed in the spectral responses between the normal and cancerous cell nuclei in each zone, which depend on the pH level of the cell nucleus. Cancerous gastric cells are precisely identified according to these features. The average cancer-cell identification accuracy obtained with a backpropagation algorithm program trained with these features is 95%.

Enhanced 2.7 μm mid-infrared emissions of Er 3+ via Pr 3+ deactivation and Yb 3+ sensitization in LiNbO 3 crystal

The use of Pr³⁺ codoping for enhancement of the transition of Er³⁺: ⁴I_11/2 → ⁴I_13/2 2.7 μm emissions was investigated in the Er/Yb codoped LiNbO₃ crystal for the first time. It is found that the codoped of Pr³⁺ ion in Er³⁺, Yb³⁺ and Pr³⁺ triply doped LiNbO₃ crystal (Er/Yb/Pr: LN) greatly enhances Er³⁺: 2.7 μm emission under excitation of a common 970 nm laser diode, depopulates the lower laser level of Er³⁺:⁴I_13/2, and has little influence on the higher laser level of Er³⁺:⁴I_11/2 at the same time for population inversion. The 2.7 μm emission characteristics and energy transfer were investigated in detail. The energy transition efficiency from lower laser level of Er³⁺:⁴I_13/2 to Pr³⁺:³F₄ level is as high as 0.42, indicating that the Pr³⁺ ion is an effective deactivation ion for Er³⁺ ion in LiNbO₃ crystal. These results suggest that Er/Yb/Pr: LiNbO₃ crystal may become an attractive host for developing solid state lasers at around 2.7 μm under a conventional 970 nm LD pump.

YVO 4 Raman laser pumped by a passively Q-switched Yb:YAG laser

We have experimentally demonstrated passively Q-switched (PQS) stimulated Raman scatting (SRS) emissions in an a-cut YVO4 Raman crystal in a coupled cavity, using a Yb:YAG/YAG/Cr4+:YAG/YAG composite crystal to generate the PQS fundamental laser, for the first time, to our best knowledge. At the incident pump power of 6.30 W, the Stokes average output power of 0.42 W was achieved. Due to the cascaded Raman effect, four first-Stokes lines operating at 1092.6 nm, 1125.4 nm, 1135.1 nm and 1157.0 nm and three second-Stokes lines operating at 1210.6 nm, 1263.2 nm and 1290.1 nm were generated simultaneously. It is noted that the spectral broadening of the fundamental field was observed. With the inclusion of an etalon in the fundamental cavity to suppress the spectral broadening, the average output power of the Stokes lines increased to 0.49 W and the maximum pulse energy was enhanced up to 84.30 μJ, corresponding to the diode-to-Stokes conversion efficiency of 7.78%.

Identification of microalgae by hyperspectral microscopic imaging system

ABSTRACT Harmful algal blooms can lead to serious environment problems, and thus monitoring and classifying microalgae have received increasing attention. Microcystis aeruginosa, Chlorella pyrenoidosa, and Nannochloris oculata all are small in size and have a similar morphology, which lead to discriminant difficulties using a traditional optical microscope. In this experiment, an independently developed hyperspectral microscopic imaging system was used to obtain the hyperspectral images of microalgae samples, and a hyperspectral dataset was developed through pretreated steps. Then the Fisher algorithm was employed to identify the species of the microalgae, and its sensitivity and specificity were found to be high. The result demonstrated that this method can classify the microalgae in a quick and convenient manner; in addition, the quantity and spatial information of the samples can be acquired.

Directional release of the stored ultrashort light pulses from a tunable Bragg-grating microcavity

We demonstrate numerically the ability for directionally releasing the stored ultrashort light pulse from a microcavity by means of two-pulse nonlinear interaction in a cascading Bragg grating structure. The setting is built by a chirped grating segment which is linked through a uniform segment, including a tunable microcavity located at the junction between the two components. Our simulations show that stable trapping of an ultrashort light pulse can be achieved in the setting. The stored light pulse in a microcavity can be possibly released, by nonlinearly interacting with the lateral incident control pulse. Importantly, by breaking the symmetry of potential cavity, the stably trapped light pulse can be successfully released from the microcavity to the expected direction. Owing to the induced optical nonlinearity, the released ultrashort light pulses could preserve their shapes, propagating in a form of Bragg grating solitons through the uniform component, which is in contrast to the extensively studied light pulse trappings in photonic crystal cavities which operate at the linear regime.

Enhanced 573 nm yellow emissions of Dy^3+ via Tb^3+ deactivation in Na_2Gd_4(MoO_4)_7 crystal

A Dy3+/Tb3+ co-doped Na2Gd4(MoO4)7 yellow laser crystal was successfully grown and analyzed. The use of Tb3+ codoping for enhancing the Dy3+:4F9/2→6H13/2 yellow emissions was investigated in the Na2Gd4(MoO4)7 crystal for the first time. In comparison to Dy3+ single-doped Na2Gd4(MoO4)7 crystal, the Dy3+/Tb3+ co-doped Na2Gd4(MoO4)7 crystal possessed a higher fluorescence branching ratio (80.2%), transition probability (3704 s−1), and fluorescence emission cross section (1.34×10−20 cm2) corresponding to the laser transition 4F9/2→6H13/2 of Dy3+. It was found that the introduced Tb3+ enhanced the 573 nm emission by depopulating the population of the laser lower level Dy3+: 6H13/2, and has little influence on the laser upper level Dy3+: 4F9/2 at the same time. These results suggest that Dy3+/Tb3+ co-doped Na2Gd4(MoO4)7 crystal may be an attractive host for developing solid state lasers at around 573 nm under a conventional 450 nm LD.

High-efficiency broadband anti-Stokes emission from Yb 3+ -doped bulk crystals

We investigate the broadband anti-Stokes emission (BASE) from Yb3+-doped crystals with a laser diode (LD) pumping at 940 nm. Our experiment reveals that Yb3+-doped crystals with random cracks are able to generate bright BASE at room temperature and atmospheric pressure. By examining the various characteristics of the crystals and the emitted light, we supply a theory for interpreting the underlying physics for this variety of BASE. In particular, we take into consideration the effects of energy migration, avalanche process, and charge-transfer luminescence. This represents the first time, to the best of our knowledge, that BASE was obtained from Yb3+-doped bulk crystals with a high optical-optical efficiency.

Enhanced 1.4 μm emissions of Tm 3+ via Tb 3+ deactivation in (Gd 0.5 Lu 0.5 ) 2 SiO 5 crystal

The use of Tb3+ codoping for the enhancement of the transition of Tm3+:3H4→3F4 ∼1.4 μm emissions was investigated in the Tm3+/Tb3+ codoped (Gd0.5Lu0.5)2SiO5 (Tm/Tb:GLSO) crystal for the first time. The ∼1.4 μm fluorescence emission properties and energy transfer mechanism of the as-grown crystals were investigated in detail. It is found that the codoped of Tb3+ ion in Tm/Tb:GLSO crystal greatly enhances Tm3+:1.4 μm emission under excitation of a common 789 nm laser diode, depopulates the lower laser level of Tm3+:3F4, and has little effect on the upper laser level of Tm3+:3H4 at the same time. The energy transfer efficiency from the Tm3+:3F4 level to the Tb3+:7F0 level is as high as (74.4±1.5)%, indicating that the Tb3+ ion is an effective deactivation ion for enhancing the ∼1.4 μm emission in Tm/Tb:GLSO crystal. These results suggest that Tm/Tb:GLSO crystal may be a promising material for ∼1.4 μm laser under the pump of a conventional 789 nm LD.

Multihyperspectral Microscopic Imaging for the Precise Identification of Pollen

ABSTRACT We report a method for precisely identifying and locating the pollen of different species in a microscope based on multihyperspectral imaging. Since pollen species are complicated and difficult to identify by one feature, both fluorescence and transmission spectral images of the samples were obtained and used for the identification together with their morphologic features. Three different species of pollens were used as test samples for investigation. The results showed that the accuracy reached 99.5%, which was a significant improvement comparing with the single spectral detection. Because more information was taken into consideration, this method has great potential for the precise identification of biological specimens.