Double-pass Pumping Research Articles

Theoretical and experimental investigation of singly resonant optical parametric oscillator under double-pass pumping.

The singly resonant optical parametric oscillator (SRO) under double-pass pumping in a two-mirror linear cavity is investigated theoretically and experimentally. Different output couplers are used in the periodically poled lithium niobate based SRO to optimize the extracted signal output. When the 2.5% output coupler is used, a pump threshold as low as 3.7 W is achieved, and 6.2 W of signal at 1.56 μm with the linewidth of 62.5 kHz is obtained at pump power of 14.5 W. The measured signal frequency drift and peak-to-peak power fluctuation are less than ±40 MHz and ±0.9% in a given 1 h, respectively.

Varying clad-core ratio fiber design for efficient lasing at 976 nm

We propose and theoretically analyze an ytterbium-doped double-clad fiber with tapered pump cladding for efficient lasing at 976 nm. Varying, rather than uniform, clad-core ratio is designed to achieve the uniform pump-intensity profile beyond the transparent pump intensity. The output power of the proposed tapered 80/250 fiber at 976 nm can be 1 kW with an optic–optic efficiency around 70% and a peak-to-peak signal-to-noise ratio over 20 dB within 3 m long fiber under the double-pass pumping scheme.

Compact infrared continuous-wave double-pass single-frequency doubly-resonant OPO

We demonstrate a compact continuous-wave single-frequency doubly-resonant optical parametric oscillator (DRO) in a double-pass pump configuration with a control of the relative phase between the reflected waves. The nested DRO cavity allows single longitudinal mode operation together with low threshold and high efficiency. Thermal effects are managed by chopping the pump beam, allowing continuous tuning of the emitted wavelength. The infrared idler wave (3200–3800nm) can be used for gas detection and the threshold pump power is compatible with diode pumping.

Fiber optical parametric amplifier with double-pass pump configuration

Characteristics of fiber optical parametric amplifier (FOPA) with double-pass pump configuration are experimentally investigated. The double-pass pump FOPA exhibits more than two-fold steeper gain slope in comparison to the conventional FOPA due to elongation of effective fiber length. In the L-band amplification band, a secondary idler is generated and used as the transmission signal in lieu of the original L-band signal. Gain measurement and bit error rate experiments are performed on the secondary idler and the results prove the usability of secondary idler, which is potentially useful for distribution networks.

2.1 μm four-mirror standing-wave optical parametric oscillator with high brightness and efficiency

We report a high-brightness and high-efficiency degenerate periodically poled MgO:LiNbO3 (PPMgLN) optical parametric oscillator (OPO), configured with a four-mirror standing-wave cavity and pumped by a Q-switched Nd:YVO4 laser. Attributed to the successful mode matching of four-mirror standing-wave cavity, we have obtained good beam qualities both in single-pass and double-pass geometry. The beam qualities of single-pass pump geometry are M2 ∼ 1.6 and 1.7 in the horizontal and vertical directions, and the beam qualities of double-pass pump geometry are M2 ∼ 1.8 and 1.9. Optical to optical conversion efficiencies of 38% and 55% are achieved, respectively. With a volume Bragg grating used as the output coupler, we achieved a narrow linewidth of less than 2 nm.

An Ho:YAG Laser with Double-Pass Pumping and the ZnGeP2 OPO Pumped by the Ho:YAG Laser

We report an efficient Ho:YAG laser end pumped by Tm:YLF lasers with double-pass pumping. We achieve the maximum continuous wave (CW) output power of 46.0 W with a single-pass pumping and 50.2 W with a double-pass pumping, corresponding to a slope efficiency of 58.0% and 62.8%, respectively. In addition, we use the Ho:YAG laser as a pumping source of the ZnGeP3 optical parametric oscillator (OPO) and obtain the maximum average output power of 14.2 W with a linear cavity and 17.0 W with a ring resonator, respectively.

Continuous wave tunable fiber optical parametric oscillator with double-pass pump configuration

We demonstrate a continuous wave tunable fiber optical parametric oscillator in a Fabry–Perot cavity consisting of a 500-m highly nonlinear fiber. In this work, the pump propagates in both directions together with the signal, thus making full use of its parametric gain. The resultant laser peak power is uneven across the wavelength range of interest due to wavelength-dependent phase modulation by the single-mode fiber sections in the cavity. This can be solved by filtering the idler spectral component from the oscillating cavity.

Sub-nanosecond, 1–10 kHz, low-threshold, non-critical OPOs based on periodically poled KTP crystal pumped at 1,064 nm

We employed a 9-mm long periodically poled KTiOPO4 (PPKTP) crystal in an optical parametric oscillator (OPO) to generate sub-nanosecond idler pulses around 2.8 μm. With a 1-cm long OPO cavity in a singly resonant configuration and double pass pumping by 1-ns pulses at 1,064 nm, the maximum idler energy reached 110 μJ at 1 kHz. Pumping with 500 ps pulses at 1–10 kHz, resulted in an idler energy of ~50 μJ and the shortest pulse duration of ~250 ps, ever reported for an OPO. The corresponding quantum conversion efficiencies were 32.5 and 34.9 %, respectively.

A miniature ultrabright source of temporally long, narrowband biphotons

We demonstrate a miniature source of long biphotons utilizing the cluster effect and double-pass pumping in a monolithic doubly resonant parametric down-converter. We obtain a biphoton correlation time of 17.1 ns with a generation rate of 1.10×105 biphotons/(s mW) and an estimated linewidth of 8.3 MHz.

High-efficiency near-degenerate PPMgLN optical parametric oscillator with a volume Bragg grating

We demonstrate a high-efficiency near-degenerate periodically poled MgO:LiNbO(3) (PPMgLN) optical parametric oscillator (OPO) using a volume Bragg grating (VBG) output coupler (OC) pumped by a multilongitudinal Q-switched Nd:YVO(4) laser at 20 kHz repetition rate. A total parametric power of 4.3 W with a conversion efficiency of 60% is achieved in a double-pass pump configuration. The output power improvement over the case of a single-pass pump is nearly 60%. Both the signal and the idler bandwidths are less than 40 GHz and are confined within 170 GHz bandwidth at 2128.8 nm. Such efficiency is, to our knowledge, the highest ever achieved from a degenerate OPO using a VBG OC.

A nanosecond optical parametric oscillator in the mid-IR region with double-pass pump

An optical parametric oscillator (OPO) with double-pass pump based on MgO:PPLN and PPLN periodic structures is described. A compact nanosecond Nd:YLF laser has been used as a pump source at 1.053 μm (the pumping pulse duration is 5–7 ns at a maximum pulse energy of 300 μJ at frequencies of 1–7 kHz). The oscillation threshold of the OPO based on MgO:PPLN was varied in a range of 11–28 μJ at wavelength of 2.1–4.3 μm. The conversion efficiency from the pump wave to an idler wave decreased from 8.6 to 2.5% in the range of 2.0–4.3 μm. For PPLN-OPO the measured threshold was 36 μJ at 4.2 μm and 49 μJ at 4.7 μm. The conversion efficiency of the pump energy into the energy of an idler wave was 3.3μ-0.4% at wavelengths of 4.2–4.7 μm.

DETERMINATION OF OPTIMUM REFLECTANCE OF OUTPUT COUPLER IN NANOSECOND SINGLY-RESONANT OPTICAL PARAMETRIC OSCILLATOR

We investigated the signal output efficiency of a singly-resonant ns-optical parametric oscillator based on LiNbO3 with the double-pass pump as a function of reflectance (R) of the output coupler. The measured signal output exhibited a broad maximum around R ~ 35% at a fixed pump energy of 100 mJ/pulse, yielding a maximum signal output efficiency of ~ 38%. The experimental results were well-supported by the numerical calculation using a split-step beam propagation model. We also found that the same beam propagation model with one-dimensional diffraction predicts nearly the same results, enabling fast numerical determination of the optimum reflectance of the output coupler.

Compact, single-frequency, doubly resonant optical parametric oscillator pumped in an achromatic phase-adapted double-pass geometry

We report on a nested-cavity, doubly resonant optical parametric oscillator (NesCOPO) architecture for widely tunable, mid-IR, single-frequency generation. By use of an achromatic phase-adapted double-pass pumping scheme, this new, low-threshold, semimonolithic architecture only requires two free-standing cavity mirrors and a nonlinear crystal with a mirror coating deposited on its input facet while the other facet is antireflection coated. It is thus as simple and compact as any basic linear optical parametric oscillator cavity, is easily tunable, and displays low sensitivity to mechanical vibrations. Using a high-repetition-rate (4.8 kHz) microlaser as the pump source of the NesCOPO, we demonstrate a compact source that provides pulsed, stable single-frequency output over a wide spectral range (3.8-4.3 μm) with a high peak power (up to 50 W), which are properties well suited for practical gas sensing applications.

Spectral hole burning for ultrasound-modulated optical tomography of thick tissue

We apply spectral hole burning (SHB)-aided detection in ultrasound-modulated optical tomography (UOT) to image optical heterogeneities in thick tissue-mimicking phantom samples and chicken breast tissue. The efficiency of SHB is improved by using a Tm(3+):YAG crystal of higher doping concentration (2.0-atomic%) and a double-pass pumping configuration, in which the pump beam is transmitted through the crystal twice to burn a deeper spectral hole with the available optical intensity. With the improved SHB-UOT system, we image absorbing, scattering, and phase objects that are embedded in the middle plane of a 30-mm-thick phantom sample. The imaging resolution was 0.5 mm in the lateral direction, as defined by the focal width of the ultrasonic transducer, and 1.5 mm in the axial direction, as determined by the ultrasonic burst length. We also image two absorbing objects embedded in a 32-mm-thick chicken breast sample. The results suggest that the improved SHB-UOT system is one step closer to the practical optical imaging application in biological and clinical studies.

Distributions of temperature and thermoelastic stresses in a thin disk active element with an arbitrary optical density

Stationary distributions of temperature and thermoelastic stresses (thermal tensions) are obtained in an active disk element with an arbitrary optical density upon a double-pass pumping. It is shown that the temperature distribution is determined by the sum of three terms: two exponential and a linear one, the exponential terms being preserved with changing the boundary conditions while the linear term producing no thermal tensions changes. It is found that thermal tensions decrease with increasing the absorption coefficient both for the constant thickness of the disk and for the constant optical density. The assessed values of the temperature are calculated during the local heating of a thin disk when the diameter of the pumped region is comparable with the disk thickness.

ASE suppression in a high energy Titanium sapphire amplifier

The energy required to generate ultrashort pulses with petawatt peak power from a Ti:sapphire laser system is a few tens of joules. To achieve this, the final amplifier must have a gain region of around 5 cm diameter that is uniformly pumped at high fluence. The high level of amplified spontaneous emission (ASE) in such an amplifier will seriously degrade its performance unless care is taken to minimise the transverse gain and the internal reflections from the crystal edges. In developing the amplifiers for the Astra Gemini laser system, we have combined the techniques of beam homogenisation and double-pass pumping of a lightly-doped crystal with a new index-matched absorber liquid. Our results demonstrate that this combined approach successfully overcomes the problem of gain depletion by ASE in a high-energy Ti:sapphire amplifier.

Improved efficiency of a pulsed optical parametric oscillator by delayed double-pass pump

By delaying the second pass of the pump of a singly resonant optical parametric oscillator, the conversion efficiency can be improved. We show the experimental results of an intracavity-doubled singly resonant parametric oscillator pumped by a Q-switched laser. Using 0.49 mJ of pump energy at 532 nm from a diode-pumped Nd:YAG laser, 0.085 mJ of 488 nm was obtained with the optimum delay for the second pass of the pump, giving a conversion efficiency of 17%. The improvement over the case of a single-pass pump was 85%, and the improvement over the double-pass pump with a small delay was 40%.

High-power, continuous-wave, singly resonant optical parametric oscillator based on MgO:sPPLT

We report a high-power, widely tunable, cw singly resonant optical parametric oscillator (OPO) based on MgO:sPPLT. The OPO is pumped in the green by a cw diode-pumped Nd:YVO(4) laser at 532 nm and can provide continuously tunable output across 848-1430 nm. Using a 30 mm crystal and double-pass pumping, an oscillation threshold of 2.88 W has been obtained, and single-pass idler powers in excess of 1.51 W have been generated over 1104-1430 nm for 6W of pump power at an extraction efficiency of 25.2% and photon conversion efficiency of 56.7%.

Experimental Investigation of Tm3+-Doped SilicaDouble-Cladding Fibre Laser

Using a Tm3+-doped double-cladding silica fibre, we produce amaximum cw 2.2 W output at approximately 2 μm. The highestachieved slope efficiency is 29.3% respect to the launched pump power.The lowest threshold is 1.85 W using the double pass pump method withthe fibre length 2.7 m, which is the lowest reported threshold ofcladding pump of the 3H4 level. The fibre laser output peakwavelength ranges from 1.967 μm to 2.018 μm with cavity 1(R1 = 1 and R2 = 0.04) and from 1.95 μm to 1.99 μm withcavity 2 (R1 = 0.04 and R2 = 0.04), as the fibre length varies.

Theoretical models for the extracavity Raman laser with crystalline Raman medium

The rate equation model of an extracavity Raman laser is deduced for the first time to the best knowledge of the authors. The normalized radiation transfer equations of the extracavity Raman laser are given. The normalized radiation transfer equations and rate equations were solved numerically to find the optimum reflectivity of the output coupler to realize the maximum conversion efficiency at the first Stokes for both the single and double-pass pumping configurations. Also, the pulse duration of the first Stokes was investigated numerically. The rate equations are verified to be a good approximation to the radiation transfer equations for the regime of low Raman gain and long pump pulse duration. Furthermore, it is found that the optimum reflectivity of the first Stokes and the second Stokes threshold are influenced significantly by the minor feedback of the resonator mirror at the second Stokes.