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We present a uniquely versatile and efficient mirror system capable of real-time fine-tuning in reflection and transmission properties across a broad wavelength range and at a high optical power. Leveraging the principles of the non-cyclic geometric phase (GP) acquired by the clockwise and counterclockwise beams of the Sagnac interferometer satisfying the anti-resonant condition on propagation through the quarter-wave plate, half-wave plate, and quarter-wave plate combination having fast axes oriented at 45° (fixed), θ (variable), and −45° (fixed) with respect to the vertical, respectively, our mirror system offers dynamic transmission control across 0–100% without the need for realignment. Notably, the GP-based mirror (GP-mirror) preserves the polarization state of the reflected beam, making it ideal for polarization-sensitive applications. The wavelength insensitivity of the GP enables seamless operation of the mirror across a wide wavelength range. As a proof-of-principle, we use the GP-mirror as the output coupler of a continuous-wave, green-pumped, doubly resonant optical parametric oscillator (DRO) based on a 30-mm-long MgO:sPPLT crystal and obtain stable operation at high powers over a wide wavelength tuning range. For a pump power of 5 W, the DRO provides an output power of 2.45 W at an extraction efficiency as high as 49% when operated at optimum output coupling. The DRO shows a maximum pump depletion of 89% and delivers an optimum output power across a tuning range ≥90 nm. The demonstrated concept offers a promising approach for advancing the capabilities and control of coherent optical sources tunable across different spectral regions and in all time scales from continuous-wave to ultrafast femtosecond domain. [ABSTRACT FROM AUTHOR]

We report on an imaging-inspired measurement of orbital angular momentum (OAM) using only a simple tilted lens and an intensified charged coupled device camera, allowing us to monitor the propagation of OAM structured photons over distance, which is crucial for free-space quantum communication networks. We demonstrate the measurement of OAM orders as high as ls = 14 in a heralded single-photon source and show, for the first time, the imaged self-interference of photons carrying OAM in a modified Mach–Zehnder interferometer. The described methods reveal both the charge and order of a photon's OAM and provide a proof of concept for the interference of a single OAM photon with itself. Using these tools, we are able to study the propagation characteristics of OAM photons over a distance, which is important for estimating transport in free-space quantum links. By translating these classical tools into the quantum domain, we offer a robust and direct approach for the complete characterization of a twisted single-photon source, an important building block of a quantum network. [ABSTRACT FROM AUTHOR]

We report a high-power source of continuous-wave (cw) mid-infrared (mid-IR) radiation at 2.26 μm based on difference-frequency-generation (DFG) of a cw Yb-fiber laser at 1.064 μm and a cw Tm-fiber laser at 2.010 μm in MgO:PPLN. Using a 50-mm-long crystal with a single grating period of 32.16 μm$ and a simple single-pass setup, we generate up to 3.84 W of cw output power at 2.26 μm at a power conversion efficiency of ~0.47%/W. The DFG output beam is characterized by a Gaussian TEM00 spatial profile with M2 < 1.2, and exhibits excellent passive power stability of 0.6% rms and spectral stability better than 0.01% over 1 hour. We find close agreement between the measured conversion efficiencies and theoretical predictions, confirming optimum performance of the DFG source. Our approach represents a viable and practical alternative to the existing methods for generating this useful wavelength. To the best of our knowledge, the generated output represents the highest cw power obtained from any single-pass nonlinear frequency conversion source in the mid-IR. [ABSTRACT FROM AUTHOR]

The authors describe the exploitation of group-velocity-matching in femtosecond optical parametric oscillators (OPOs) for enhanced down-conversion efficiency into the mid-infrared (mid-IR). We demonstrate the concept in a femtosecond OPO based on a long MgO:PPLN crystal, for the first time, by utilizing group-velocity-matching between pump and idler pulses. Taking advantage of the wide phase-matching bandwidth when pumped near 1 µm enables the use of a 42-mm-long crystal, resulting in an oscillation threshold as low as 5 mW, pump depletion of 78%, and an idler quantum conversion efficiency up to 48% into the mid-IR. Using 80–100 fs pump pulses tunable across 997–1070 nm, we have generated idler radiation across 3132–4273 nm (2340–3193 cm−1) with spectral bandwidth of 140–180 nm, providing up to 65 mW of average power at 80 MHz repetition rate. The near-IR signal is tunable across 1392–1568 nm, with up to 76 mW of average power in transform-limited pulses of ∼400–600 fs duration without dispersion compensation. Preferential operation at group-velocity-matched wavelengths leads to intrinsically high passive power stability with <1% rms fluctuation over 1 h for both signal and idler. With the capability for rapid pump tuning in the mid-IR, this OPO represents a viable source for spectroscopic applications, which we demonstrate using CH4 gas. Extension to other quasi-phase-matched nonlinear crystals is also discussed. [ABSTRACT FROM AUTHOR]

We report a high-repetition-rate picosecond fiber-based source at 2.1 µm offering exceptional performance capabilities over existing lasers near this wavelength, providing high average power and efficiency together with excellent spectral, power and beam pointing stability, in high spatial beam quality. This new source is based on a near-degenerate MgO:PPLN optical parametric oscillator (OPO) pumped by an Yb-fiber laser at 1064 nm, and incorporating a diffraction grating for spectral control. The device provides as much as 7.1 W of average power at 2.1 µm for a pump power of 18 W at an extraction efficiency of 39.4% in pulses of 20 ps at 79.3 MHz. The output exhibits passive power stability better than 1% rms over 15 hours, and a beam pointing stability ∼40 µrad over 1 hour, in high spatial quality with M2 ∼ 3.5. The output beam is linearly polarized and the pulse train has an amplitude stability better than 3.4% rms over 2 µsec. Radio-frequency measurements of the output pulse train also confirm high temporal stability and low timing jitter, indicating that the source is ideal for variety of applications including pumping long-wavelength mid-infrared OPOs. Photograph shows the temperature-controlled, 50-mm-long MgO:PPLN crystal inside the cavity, used as nonlinear gain medium in the picosecond source operating at 2.1 µm. The visible light is the result of non-phase-matched second harmonic generation of the pump beam in the MgO:PPLN crystal. [ABSTRACT FROM AUTHOR]

We report a stable, high-power, high-repetition-rate, picosecond green source at 532 nm in a compact and practical design based on single-pass second-harmonic generation (SHG) of a mode-locked ytterbium fiber laser in the nonlinear material BiB3O6. Using a 10-mm-long crystal, we have generated as much as 5.4 W of picosecond green radiation at 80 MHz for a fundamental average power of 14.2 W at a single-pass SHG conversion efficiency of 38%. The green output power exhibits excellent passive stability of 0.24% rms over 15 h, has a TEM00 spatial profile with M2 < 1.93, and a beam pointing stability <9 μrad over 1 h without active control. [ABSTRACT FROM AUTHOR]

A novel technique for coupling of two resonant optical cavities using an antiresonant ring (ARR) interferometer is reported. By deploying two synchronously-pumped femtosecond optical parametric oscillators (OPOs), it is shown that the use of an ARR can provide an intracavity common path for the two oscillating fields, but without gain coupling between the two nonlinear media. The new technique permits the generation of two signal (idler) wavelengths, which can be independently and arbitrarily varied across the OPO tuning range. The absence of gain coupling also enables unrestricted and uninterrupted tuning through wavelength degeneracy at any arbitrary point within the OPO tuning range. It is shown that signal wavelength pairs tunable across 1500-1580 nm, corresponding to a frequency separation from ∼ 10 THz down to exact degeneracy, can be generated from the coupled OPOs, limited only by the reflectivity of the available mirrors. [ABSTRACT FROM AUTHOR]

Efficient frequency conversion of high-repetition-rate femtosecond and picosecond pulses with wide tunability throughout the visible, blue, and UV is demonstrated in the nonlinear optical crystal BiB3O6 (BIBO). Using direct single-pass second harmonic generation of Kerr-lens-mode-locked Ti:sapphire laser, average output powers close to 1 W at conversion efficiencies in excess of 50% are demonstrated with broad spectral coverage across 370-450 nm in the near-UV and blue spectral range. Output pulse durations of 220 fs and 2.8 ps have been obtained at a pulse repetition rate of 76 MHz. By implementing a synchronously pumped femtosecond optical parametric oscillator (OPO) based on BIBO, the generated spectral range is further extended to cover the entire visible spectrum, across the green-yellow-orange-red regions. Average output powers of up to 270 mW in pulses of 120 fs at 76 MHz repetition rate have been generated across the 480-710 nm range. Internal frequency doubling of the visible OPO signal pulses in the crystal of beta-BaB2O4 has permitted high-repetition-rate femtosecond pulse generation with wide tunability across 250-350 nm in the UV at up to 100 mW of average power. The potential of BIBO for efficient frequency conversion of high-intensity pulses is also demonstrated through third harmonic generation of amplified microjoule picosecond pulses at 1064 nm. Output pulse energies of 216 muJ in 29 ps duration at 25 Hz repetition rate have been obtained at 355 nm with overall conversion efficiencies of up to 50%. [ABSTRACT FROM PUBLISHER]