Optical coherence tomography (OCT) is a powerful three-dimensional (3D) imaging modality with micrometer-scale axial resolution and up to multi-GigaVoxel/s imaging speed. However, the imaging range of high-speed OCT has been limited. Here, we report 3D OCT over cubic meter volumes using a long coherence length, 1310 nm vertical-cavity surface-emitting laser and silicon photonic integrated circuit dual-quadrature receiver technology combined with enhanced signal processing. We achieved 15 µm depth resolution for tomographic imaging at a 100 kHz axial scan rate over a 1.5 m range. We show 3D macroscopic imaging examples of a human mannequin, bicycle, machine shop gauge blocks, and a human skull/brain model. High-bandwidth, meter-range OCT demonstrates new capabilities that promise to enable a wide range of biomedical, scientific, industrial, and research applications.

Cubic meter volume optical coherence tomography

We report generation of the second, third, fourth, and fifth harmonics of the output of a Yb-doped fiber amplifier seeded by a passively Q-switched Nd:YAG microchip laser. We obtained high conversion efficiencies using a simple optical arrangement and critically phase-matched nonlinear crystals. Starting with 320 mW of average power at 1064 nm (86 μJ per pulse at a 3.7 kHz repetition rate), we generated 160 mW at 532 nm, 38 mW at 355 nm, 69 mW at 266 nm, and 18 mW at 213 nm. The experimental results are in excellent agreement with calculations.

Efficient second, third, fourth, and fifth harmonic generation of a Yb-doped fiber amplifIer.

A laser system includes a first laser diode configured to generate first light in a first direction along an optical path; a laser resonator having a gain medium, anisotropic saturable absorber, and a wavelength selective outcoupler positioned in the optical path upon which the first light impinges a first side thereof so as to pump the gain medium (first light from the first laser diode is absorbed in the gain medium), a second laser diode configured to generate second light in a second direction along the optical path toward a second side of the resonator, passes through the wavelength selective outcoupler unimpeded and is absorbed by the saturable absorber element, wherein the second light has a polarization corresponding to the orientation of the saturable absorber; the wavelength selective outcoupler is configured to only allow third light of a predetermined wavelength to have feedback in the laser resonator, achieve gain in the resonator, and be emitted from the laser resonator. A method for forming a laser system is also described.

Low timing jitter, single frequency, polarized laser

A passively Q-switched dual-wavelength solid-state laser is presented. The two wavelengths are emitted by two different crystals in order to avoid gain competition, and the synchronization between the pulses is obtained by external triggering of the saturable absorber. Sum frequency mixing is demonstrated, proving the interest of this source for terahertz generation in the 0.3-0.4 THz range through difference frequency generation.

Simultaneous passively Q-switched dual-wavelength solid-state laser working at 1065 and 1066 nm.

In this paper, a side diode pumped passively Q-switched Nd:YAG laser is presented using a Cr4+:YAG as saturable absorber. The performance of the Nd:YAG laser in the free-running and Q-switched modes is theoretically and experimentally studied with different output coupler reflectivities and different initial transmissions of Cr4+:YAG crystals. The optimum reflectivity of the output coupler is found to be 25 % in the Q-switched mode according to the theoretical calculations and experimental results. The initial transmission of Cr4+:YAG is set to 20 % in order to achieve maximum output energy in a single laser pulse. The experimental results are in good agreement with calculated values. In the Q-switched mode, single pulse output energy is obtained around 57 mJ with 10 ns pulse duration over 1–20 Hz pulse repetition rates. The optical to optical conversion efficiency reaches 14.25 %.

57 mJ with 10 ns passively Q-switched diode pumped Nd:YAG laser using Cr4+:YAG crystal

Optical triggering via direct bleaching of a Cr:YAG saturable absorber was applied to a monolithic Nd:YAG/Cr:YAG laser crystal. The method uses a single laser diode bar to bleach a thin sheet within the saturable absorber from a direction orthogonal to the lasing axis. By placing the Q-switch at the time corresponding to the steepest slope (dT/dt) for change in transmission during bleaching, the pulse-to-pulse timing jitter showed a 13.2× reduction in standard deviation, from 132 ns for free-running operation to 10 ns with optical triggering. We measured that a fluence of 60 kW/cm2 was sufficient to enable optical triggering, where a diode appropriately sized for the length of the Cr:YAG (~3 mm) would then require only ~150 W of optical power over a 1-2 μs duration to enable effective jitter reduction. Additionally, we measured an increase in optical-to-optical efficiency with optical triggering, where the efficiency improved from 12% to 13.5%.

Optical triggering of a Q-switched Nd:YAG laser via transverse bleaching of a Cr:YAG saturable absorber.

We present a compact, side pumped passively Q-switched Yb:YAG laser that was operated in a burst mode with pump durations of 2-4 ms at low duty cycles. Intra-pump pulse Q-switched pulse repetition frequencies varied from 5-20 kHz depending on the transmission of the Cr:YAG saturable absorber, which was varied from 70% to 94%. Pump duration, pulse repetition frequency and output coupler reflectivity were optimized to yield maximum Yb:YAG laser average power and laser efficiency, while providing sufficient peak intensity, typically 0.3-1 MW, to enable efficient forth harmonic generation (FHG). Pulse energies and durations were in ranges of 0.3-1.8 mJ and 1.5-7ns, respectively, dependent on the unbleached transmission of the Cr:YAG saturable absorber. We achieved an optical efficiency of greater than 15% for the Yb:YAG laser. Extra-cavity 515 nm second harmonic generation (SHG) was achieved using a 5mm long KTP crystal. The 515 nm light was then frequency doubled by focusing it into a 7mm long BBO crystal, resulting in a 15% conversion efficiency from 1030nm to 257.5 nm, with an average UV power greater than 100 mW.

UV by the fourth harmonic generation of compact side-pumped Yb:YAG laser emission

To address the issue of pulse-to-pulse timing jitter in a passively Q-switched Cr:YAG/Nd:YAG laser, we have
developed a technique for optical triggering, where the energy from a single bar diode was used to bleach a thin sheet
within the Cr:YAG saturable absorber from a direction orthogonal to the lasing axis. A strong anisotropy for bleaching
effect was observed; with appropriate polarization of the bleaching light the transmission through the saturable absorber
was increased from 45% to 63%. This technique was applied to a monolithic Cr:YAG/Nd:YAG laser operating under
steady state conditions. By placing the Q-switched pulse at the time corresponding to the steepest slope for change in
transmission during bleaching, which occurs ~1μs after the bleaching diode trigger, we measured an 12.5X reduction in
the pulse-to-pulse timing jitter, from 100ns for free running operation to 8ns with optical triggering.

Reduction in timing jitter for a Cr:YAG Q-switched Nd:YAG laser

A compact 1030nm fiber laser for ultraviolet generation at 257.5nm is presented. The laser employs a short length of highly-doped, large core (20μm), coiled polarization-maintaining ytterbium-doped double-clad fiber pumped by a wavelength-stabilized 975nm diode. It is passively Q-switched via a Cr 4+ :YAG saturable absorber and generates 2.4W at 1030nm in a 110μJ pulse train. Lithium triborate (LBO) and beta-barium borate (BBO) are used to achieve 325mW average power at the fourth harmonic. The laser's small form factor, narrow linewidth and modest power consumption are suitable for use in a man-portable ultraviolet Raman explosives detection system.

Compact frequency-quadrupled pulsed 1030nm fiber laser

Coherent optical frequency-domain reflectometry (C-OFDR) is a distance measurement technique with significant sensitivity and detector bandwidth advantages over normal time-of-flight methods. Although several swept-wavelength laser sources exist, many exhibit short coherence lengths, or require precision mechanical tuning components. Semiconductor distributed feedback lasers (DFBs) are advantageous as a mid-to-long range OFDR source because they exhibit a narrow linewidth and can be rapidly tuned simply via injection current. However, the sweep range of an individual DFB is thermally limited. Here, we present a novel high-resolution OFDR system that uses a compact, monolithic 12-element DFB array to create a continuous, gap-free sweep over a wide wavelength range. Wavelength registration is provided by the incorporation of a HCN gas cell and reference interferometer. The wavelength-swept spectra of the 12 DFBs are combined in post-processing to achieve a continuous total wavelength sweep of more than 40 nm (5.4 THz) in the telecommunications C-Band range.

Optical frequency-domain reflectometry using multiple wavelength-swept elements of a DFB laser array

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