Atomic frequency standard based on direct frequency comb spectroscopy.

We have developed a high performance atomic frequency standard based on Doppler-free direct frequency comb excitation of a two-photon transition in Rb. We demonstrate equivalent performance compared to an identical system based on cw laser excitation of the clock transition. This approach greatly simplifies optical clock architecture and eliminates the need for cw lasers in many two-photon frequency standards.

Ultralow-quantum-defect single-frequency fiber laser.

A single-frequency distributed-Bragg-reflector fiber laser at 980 nm with a quantum defect of less than 0.6% was developed with a 1.5-cm 12 wt% ytterbium-doped phosphate fiber pumped by a 974.

Injection-locked highly Yb-doped uncoupled-61-core phosphate fiber laser.

Uncoupled multicore fibers are promising platforms for advanced optical communications, optical computing, and novel laser systems. In this paper, an injection-locked highly ytterbium (Yb)-doped uncoupled-61-core phosphate fiber laser at 1030 nm is reported. The 61-core fiber with a core-to-core pitch of 20 μm was fabricated with the stack-and-draw technique.

Single-frequency fiber laser at 880 nm.

Single-frequency fiber lasers with extremely low noise and narrow spectral linewidth have found many scientific and practical applications. There is great interest in developing single-frequency fiber lasers at new wavelengths. In this paper, we report a single-frequency Nd-doped phosphate fiber laser operating at 880 nm, which is the shortest demonstrated wavelength for a single-frequency fiber laser thus far, to the best of our knowledge.

Magneto-optical properties of highly Dy doped multicomponent glasses.

Due to their large effective magnetic moment, Dy-doped materials have attracted much interest for magneto-optical applications. In this paper, we report highly Dy doped multicomponent glasses with concentrations from 40 wt.% to 75 wt.

Investigation of ion-ion interaction effects on Yb-doped fiber amplifiers.

Ytterbium (Yb)-doped materials have been widely used for high efficiency high energy laser sources at the 1 µm wavelength region because of their very low quantum defect and the unique simple energy level structure of Yb, resulting in no excited-state absorption and low occurrence probability of deleterious ion-ion interaction processes. It has been generally recognized that these ion-ion interaction processes have very little influence on the operation of Yb-doped fiber lasers at low and moderate power levels. However, our recent study shows that the performance of Yb-doped fiber amplifiers operating at low power levels is still influenced by the ion-ion interaction processes due to the large amount of population at the upper laser level F.

Power scalable 10 W 976 nm single-frequency linearly polarized laser source.

A 10 W level 976 nm single-frequency linearly polarized laser source was demonstrated with a two-stage all-fiber amplifier configuration. The continuous-wave output power of 10.1 W was obtained from the second stage amplifier by using a 20/130 μm single-mode, polarization maintaining, 1.

Single-frequency blue laser fiber amplifier.

An all-fiber amplifier for a single-frequency blue laser was demonstrated for the first time, to the best of our knowledge. Over 150 mW continuous-wave single-transverse-mode blue laser output was obtained with a 10 m 1000 ppm thulium-doped fluoride fiber pumped by a 1125 nm fiber laser at a power of 2 W. The output power was limited due to the onset of the competitive lasing at 783 nm.

Graphene Q-switched Ho(3+)-doped ZBLAN fiber laser at 1190 nm.

We report Q-switched pulse operation of holmium (Ho(3+))-doped ZrF(4)-BaF(2)-LaF(3)-AlF(3)-NaF (ZBLAN) at ∼1190  nm in an all-fiber ring laser by using a fiber-optic graphene saturable absorber, which was fabricated by depositing graphene onto the flat surface of a side-polished D-shaped fiber. Stable Q-switched operation was established at a pump power of 180 mW with a repetition rate of 24 kHz and pulse width of 5.7 μs.

Watt-level short-length holmium-doped ZBLAN fiber lasers at 1.2 μm.

In-band core-pumped Ho3+-doped ZBLAN fiber lasers at the 1.2 μm region were investigated with different gain fiber lengths. A 2.

All-fiber fundamentally mode-locked 12 GHz laser oscillator based on an Er/Yb-doped phosphate glass fiber.

We have developed a compact and stable all-fiber fundamentally mode-locked 12 GHz laser system. The passively mode-locked laser centered at 1535 nm has temporal pulse width of ∼2  ps and average power of 5 mW. The timing jitter, which is cumulative from pulse-to-pulse, has been measured using an optical cross-correlation method and found to be 44  fs/pulse.

Monolithic fiber chirped pulse amplification system for millijoule femtosecond pulse generation at 1.55 µm.

A monolithic fiber chirped pulse amplification system that generates sub-500 fs pulses with 913 µJ pulse energy and 4.4 W average power at 1.55 µm wavelength has recently been demonstrated.

High efficiency, monolithic fiber chirped pulse amplification system for high energy femtosecond pulse generation.

A novel monolithic fiber-optic chirped pulse amplification (CPA) system for high energy, femtosecond pulse generation is proposed and experimentally demonstrated. By employing a high gain amplifier comprising merely 20 cm of high efficiency media (HEM) gain fiber, an optimal balance of output pulse energy, optical efficiency, and B-integral is achieved. The HEM amplifier is fabricated from erbium-doped phosphate glass fiber and yields gain of 1.

Single-frequency Ho(3+)-doped ZBLAN fiber laser at 1200 nm.

A single-frequency (SF) fiber laser at 1200 nm was developed with a distributed Bragg reflector (DBR) configuration by splicing a 22 mm long highly holmium-doped ZBLAN (ZrF(4)-BaF(2)-LaF(3)-AlF(3)-NaF) fiber with a pair of silica fiber Bragg gratings. The linewidth was estimated to be less than 100 kHz based on the measured frequency noise. The relative intensity noise was measured to be <110 dB/Hz at the relaxation oscillation peak and the polarization extinction ratio was measured to be >19 dB.

976 nm single-frequency distributed Bragg reflector fiber laser.

A single-frequency distributed Bragg reflector (DBR) fiber laser at 976 nm was developed with a 2 cm long highly ytterbium-doped phosphate fiber and a pair of silica fiber Bragg gratings. More than 100 mW of linearly polarized output was achieved from the all-fiber DBR laser with a linewidth less than 3 kHz. The outstanding features of this single-frequency laser also include ultralow relative intensity noise and high wavelength stability.

High peak-power single-frequency pulses using multiple stage, large core phosphate fibers and preshaped pulses.

We have developed a monolithic high power pulsed fiber laser in a master oscillator power amplifier (MOPA) configuration, which is capable of reaching 0.38 mJ pulse energy and 128 kW peak power for 3 ns pulses at ~1550 nm while maintaining transform-limited linewidth. The fiber laser pulse seed was achieved by directly modulating a CW single-frequency fiber laser using an electro-optic modulator.

220 μJ monolithic single-frequency Q-switched fiber laser at 2 μm by using highly Tm-doped germanate fibers.

We report a unique all fiber-based single-frequency Q-switched laser in a monolithic master oscillator power amplifier configuration at ~1920 nm by using highly Tm-doped germanate fibers for the first time. The actively Q-switched fiber laser seed was achieved by using a piezo to press the fiber in the fiber Bragg grating cavity and modulate the fiber birefringence, enabling Q-switching with pulse width and repetition rate tunability. A single-mode polarization maintaining large core 25 μm highly Tm-doped germanate fiber was used in the power amplifier stage.

Kilowatt-level stimulated-Brillouin-scattering-threshold monolithic transform-limited 100 ns pulsed fiber laser at 1530 nm.

We demonstrate a high-stimulated-Brillouin-scattering-threshold monolithic pulsed fiber laser in a master oscillator power amplifier configuration that can operate over the C band. In the power amplifier stage, we used a newly developed single-mode, polarization maintaining, and highly Er/Yb codoped phosphate fiber with a core diameter of 25 microm. A single-frequency actively Q-switched fiber laser was used to generate pulses in the hundreds of nanoseconds at 1530 nm.

Enhanced terahertz source based on external cavity difference-frequency generation using monolithic single-frequency pulsed fiber lasers.

We demonstrate a resonant external cavity approach to enhance narrowband terahertz radiation through difference-frequency generation for the first time (to our knowledge). Two nanosecond laser pulses resonant in an optical cavity interact with a nonlinear crystal to produce a factor of 7 enhancement of terahertz power compared to a single-pass orientation. This external enhancement approach shows promise to significantly increase both terahertz power and conversion efficiency through optical pump pulse enhancement and effective recycling.

High SBS-threshold single-mode single-frequency monolithic pulsed fiber laser in the C-band.

We report a high SBS-threshold, single-frequency, single-mode, polarization maintaining (PM) monolithic pulsed fiber laser source in master oscillator and power amplifier (MOPA) configuration that can operate over the C-band. In order to achieve a narrow transform-limited linewidth for pulses longer than 100 ns, we use a single-frequency Q-switched fiber laser seed, which itself can be seamlessly tuned up to 1.24 micros.

Multipole analysis of the radiation from near-field optical probes.

We experimentally and theoretically analyze the radiation emitted from subwavelength-sized apertures in near-field optical probes. By decomposing the experimentally obtained radiation patterns into vector spherical waves, we describe the fields in terms of a series of multipole sources. We fit polarization-resolved angular intensity distributions, measured as far as 150 degrees from the normal, with dipole, quadrupole, and octupole radiation.

Image amplifier based on Yb(3+)-doped multi-core phosphate optical fiber.

We demonstrate image amplification with a 19-pixel optical image amplifier array based on high gain per unit length Yb(3+)-doped phosphate glass optical fiber. The 19 pixels of the image amplifier provide spatially uniform image amplification whose gain can reach 30 dB/pixel or more with a fiber length of 10 cm. This image amplifier responds quickly to changes in the image position - with potential for GHz-level frame rates.

In vivo retinal optical coherence tomography at 1040 nm - enhanced penetration into the choroid.

For the first time in vivo retinal imaging has been performed with a new compact, low noise Yb-based ASE source operating in the 1 microm range (NP Photonics, lambdac = 1040 nm, Deltalambda = 50 nm, Pout = 30 mW) at the dispersion minimum of water with ~7 microm axial resolution. OCT tomograms acquired at 800 nm are compared to those achieved at 1040 nm showing about 200 microm deeper penetration into the choroid below the retinal pigment epithelium. Retinal OCT at longer wavelengths significantly improves the visualization of the retinal pigment epithelium/choriocapillaris/choroids interface and superficial choroidal layers as well as reduces the scattering through turbid media and therefore might provide a better diagnosis tool for early stages of retinal pathologies such as age related macular degeneration which is accompanied by choroidal neovascularization, i.

Diffraction by a subwavelength-sized aperture in a metal plane.

We present an experimental study on the diffraction of light by an aperture small compared with the wavelength. The aperture is illuminated by laser light guided in a metal-clad tapered optical fiber. We investigate different orientations of the aperture in the plane: normal to the cleaved plane, oblique to the cleaved plane, and off-center.

Polarization effects in near-field excitation-collection probe optical microscopy of a single quantum dot.

We solve numerically the three-dimensional vector form of Maxwell's equation for the situation of near-field excitation and collection of luminescence from a single quantum dot, using a scanning near-field optical fibre probe with subwavelength resolution. We highlight the importance of polarization-dependent effects in both the near-field excitation and collection processes. Applying a finite-difference time domain method, we calculate the complete vector fields emerging from a realistic probe structure which is in close proximity to a semiconductor surface.