Long-term Power Stability Research Articles

High-efficiency Yb:YAG thin-disk chirped pulse amplifier delivering 884-femtosecond laser with tunable repetition rates and high stability

We experimentally demonstrated a compact, highly efficient, stable, chirped pulse amplification (CPA) thin-disk regenerative system with a tunable repetition rate. The laser head consists of a 9 at. % Yb:YAG thin-disk with a diameter of 8.8 mm and a thickness of 150 μm, is designed for a 48-pump pass configuration. In CPA-based regenerative amplifier configuration, a maximal output power of 85 W at 500 kHz is achieved with a conversion efficiency of 53.1 %. This corresponds to a pulse energy of 170 μJ. To the best of our knowledge, this is the highest conversion efficiency in CPA thin-disk regenerative amplifiers. The pulse width is compressed to 884 fs with a pair of grating, resulting in a peak power of 192 MW. At 85 W, a near diffraction limit beam quality factor M2 of 1.40 is measured, which is essential in precision applications. In addition, remarkable long-term power stability is confirmed with a root-mean-square (RMS) fluctuation of 0.12 % over a 24-hour duration. The reported femtosecond amplifier is believed to be a promising tool for various applications such as extreme manufacturing, terahertz spectroscopy, etc.

Low repetition rate 915 nm figure-9 ultrafast laser with all-fiber structure.

The advent of optical metrology applications has necessitated the development of compact, reliable, and cost-effective picosecond lasers operating around 900 nm, specifically catering to the requirements of precise ranging. In response to this demand, our work introduces an innovative solution-an all-fiber, all-polarization-maintaining (PM) figure-9 mode-locked laser operating at 915 nm. The proposed figure-9 Nd-doped fiber laser has a 69.2 m long cavity length, strategically designed and optimized to yield pulses with a combination of high pulse energy and low repetition rate. The laser can generate 915 nm laser pulses with a pulse energy of 4.65 nJ, a pulse duration of 15.2 ps under the repetition rate of 3.05 MHz. The 1064 nm amplified spontaneous emission (ASE) is deliberately filtered out, in order to prevent parasitic lasing and increase the spectral proportion of the 915 nm laser. The all-PM fiber configuration of this laser imparts exceptional mode-locking performance and environmental robustness, which is confirmed by long-term output power and spectral stability test. This compact and long-term reliable fiber laser could be a promising light source for applications like inter-satellite ranging.

Watt-level broadband PM Tm-doped fiber amplifier for the 1750–1910 nm window

We report broadband experimental and simulated performance of a single-clad polarization-maintaining (PM) thulium-doped fiber amplifier (TDFA) optimized for operation in the 1750–1910 nm wavelength band. With the two-stage amplifier architecture, a maximum output power of 2.4 W was obtained at 1850 nm for 7.0 W of launched pump power at 1567 nm, with a corresponding optical-to-optical efficiency of 31.4 %. The measured polarization extinction ratio (PER) was larger than 22.6 dB, and the long-term power stability exhibited a peak-to-peak variation of 2.4 %. By employing a tunable seed laser covering the 1750–1910 nm wavelength range, we measured a maximum output power level of 2.38 W with an optical signal-to-noise ratio (OSNR) greater than 53 dB/0.1 nm. Our simulations are in good agreement with the experimental data over the whole 160 nm operating spectral bandwidth.

All-solid-state CW Pr3+:YLF green laser at 522 nm end-pumped by a high-power fiber-coupled 444 nm blue LD module

Continuous wave (CW) green lasers have a lot of important applications in many fields, including holography, interferometry, atom cooling and trapping, and quantum optics, and they are usually achieved by frequency-doubling 1 µm lasers based on the Nd3+ gain media. In this paper, we present an all-solid-state CW green laser with an output wavelength of 522 nm, which was directly attained by employing a Pr3+:YLF crystal pumped with a high-power fiber-coupled blue laser diode (LD) module as the gain medium. Due to the negative thermal lens effect of the Pr3+:YLF crystal, the designed laser resonator had to be lengthened with the increase in the incident pump power. As a result, when a 0.5% doped Pr3+:YLF crystal was employed as the gain medium and the incident pump power was 12 W, the length of the resonator was optimized to 311.3 mm and the maximum output power of 522 nm green laser was up to 886 mW. The obtained conversion efficiency and beam quality M2 were 11.25% and 1.15, respectively. The long-term power stability within 4.5 h was better than ±1.5% at an output power of 700 mW. The obtained watt-level green laser can also be used to generate high power CW deep UV laser for laser processing of silicon and organic materials, inspection, etc.

High power, widely tunable femtosecond MgO:PPLN optical parametric oscillator

We demonstrate a high power, widely tunable femtosecond MgO-doped periodically poled lithium niobate (MgO:PPLN) optical parametric oscillator (OPO) at 151 MHz, pumped by a Kerr-lens mode-locked Yb:KGW laser. With a maximum pump power of 7 W, the OPO is capable of delivering as high as 2.2 W of the signal centered around 1500 nm with tunable signal spectrum ranges of 1377 nm–1730 nm at an extraction efficiency of 31.4%, which exhibits a long-term passive power stability better than 0.71% rms over 4 h. The maximum idler bandwidths of 185 nm at 3613 nm are obtained across the idler tuning ranges of 2539 nm–4191 nm. By compensating intracavity dispersion, the signal has the shortest pulse duration of 170 fs at 1428 nm.

Directly diode-pumped femtosecond Cr:ZnS amplifier with ultra-low intensity noise.

Diode-pumped Cr:ZnS oscillators have emerged as precursors for single-cycle infrared pulse generation with excellent noise performance. Here we demonstrate a Cr:ZnS amplifier with direct diode-pumping to boost the output of an ultrafast Cr:ZnS oscillator with minimum added intensity noise. Seeded with a 0.66-W pulse train at 50-MHz repetition rate and 2.4 µm center wavelength, the amplifier provides over 2.2 W of 35-fspulses. Due to the low-noise performance of the laser pump diodes in the relevant frequency range, the amplifier output achieves a root mean square (RMS) intensity noise level of only 0.03% in the 10 Hz-1 MHz frequency range and a long-term power stability of 0.13% RMS over one hour. The diode-pumped amplifier reported here is a promising driving source for nonlinear compression to the single- or sub-cycle regime, as well as for the generation of bright, multi-octave-spanning mid-infrared pulses for ultra-sensitive vibrational spectroscopy.

Carrier-envelope phase stable few-cycle laser system delivering more than 100 W, 1 mJ, sub-2-cycle pulses

Two-stage multipass-cell compression of a fiber-chirped-pulse amplifier system to the few-cycle regime is presented. The output delivers a sub-2-cycle (5.8 fs), 107 W average power, 1.07 mJ pulses at 100 kHz centered at 1030 nm with excellent spatial beam quality (M2 = 1.1, Strehl ratio S = 0.98), pointing stability (2.3 µrad), and superior long-term average power stability of 0.1% STD over more than 8 hours. This is combined with a carrier-envelope phase stability of 360 mrad in the frequency range from 10 Hz to 50 kHz, i.e., measured on a single-shot basis. This unique system will serve as an HR1 laser for the Extreme Light Infrastructure Attosecond Light Pulse Source research facility to enable high repetition rate isolated attosecond pulse generation.

The Adoption of Chalcogenide Glass Fiber as Pulse Stretcher in an All-Fiber Structured 2 μm Chirped Pulse Amplification System

We present the development of an As <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> fiber-based reusable inline optical connector; and, for the first time to the best of our knowledge, integrated it into a 2 μm chirped pulse amplification system as the pulse stretcher. By this mechanism, a near 20 times pulse stretching ratio was achieved in 0.5 m-long this As <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> fiber and the introduction of insertion loss as low as 2.84 dB while it was connected with silica fiber. After the follow-up fiber amplification and self-compression mechanism, the laser average output power was boosted to 1.97 W and pulse duration was optimized to 2.53 ps. Moreover, to further inspect the laser pulse property, the pulses were then delivered into a 5.3 m-long ZrF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> -BaF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -LaF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -AlF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -NaF (ZBLAN) fiber which was fusion spliced to SM1950 fiber. Thanks to the 0.4-dB low fusion splice loss between these fibers, a 1.56-W supercontinuum source with bandwidth of 1.93-3.50 μm is obtained. The measured two hours of root-mean-square value of power fluctuation of this laser source is 0.13%, indicating an ultra-high long-term power stability. This work will lay a solid foundation in the realization of the all-fiber structured high-power thulium-doped fiber amplifier with high compactness.

Phase-locked picosecond optical parametric oscillator.

We report a degenerate self-phase-locked picosecond optical parametric oscillator (OPO) synchronously pumped by a mode-locked Yb-fiber laser at 1064 nm, delivering broadband output near 2 µm with 2.8 W of average power at ∼80MHz repetition rate. By exploiting a 50-mm-long MgO:PPLN crystal providing high gain and low group velocity dispersion under type-0 (e→ee) phase matching, the OPO generates a phase-locked degenerate output spectrum with a bandwidth of ∼202nm centered at 2128 nm in pulses of ∼21ps duration with excellent passive long-term power and spectral stability in high spatial beam quality. Phase-locked operation results in spectral and power stabilization at exact degeneracy and is further validated by f-2f interferometry and radio frequency measurements of OPO output. To the best of our knowledge, this is the first degenerate self-phase-locked OPO in picosecond time scale, and the highest average power reported for a phase-locked ultrafast OPO to date.

Watt-level ultra-flattened mid-infrared supercontinuum with high power stability generation in an all-fiber structured Tm-doped fiber amplifier pumped ZBLAN single-mode fiber

We demonstrate a 5-watt-level mid-infrared supercontinuum (MIR-SC) generation in a Tm-doped fiber laser (TDFL) pumped single-mode ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fiber. In the optimization of front end 2 µm laser system, the laser energy-transfer efficiency from 1.55 µm to 2 µm was improved to 25 % by using a 4 m-long single-mode Tm-doped fiber (SM-TDF), in combination with a tailored broad-band pass filter (bandwidth>1.8 µm), the pulse spectrum was well shaped, the spectral contrast was substantially improved and the follow-up laser amplification efficiency was significantly optimized. In the realization of all-fiber structured MIR-SC power boosting process, we successfully achieved the high robustness and ultra-low loss fusion splicing point between silica and ZBLAN fiber in the high power measurement condition. By comprehensively taking the above-mentioned measures, we eventually obtained a MIR-SC covering 1.9 µm to 4 µm, with average power as high as 5.4 W, power stability with a root mean square (RMS) value of 0.03 % in 2 h, spectral fluctuation less than 0.1 dB in the wavelength range from 2.1 µm to 3.5 µm and without any residual pump peaks appeared in the spectrum. To the best of our knowledge, this is the first investigation on the all-fiber structured MIR-SC generation with so high the long-term power stability and spectrum flatness simultaneously in average power of above 5-Watt level.

Orthogonally polarized dual-wavelength Nd:YVO4/MgO:PPLN intra-cavity frequency doubling green laser

An orthogonally polarized dual-wavelength laser emitting at 542 nm and 543 nm was proposed and demonstrated. The laser was based on a single Nd:YVO4 crystal and two MgO:PPLN crystals. An optical-to-optical (O-O) efficiency as high as 15.3% was achieved when the powers of the two emission wavelengths were equal. The long-term power stability was 4.5% for 542 nm and 3.5% for 543 nm, respectively. The Laser speckle contrast ratio (SCR) was also measured as a function of power ratio of the two emission wavelengths. The measured SCR values agreed with theoretical simulations with a difference less than 5%.

Compact, and efficient continues wave intra-cavity frequency doubling Nd:YVO4/MgO:PPLN 542/543 nm green lasers

Efficient, compact and low cost 542/543 nm green DPSS lasers were proposed and demonstrated. Each laser was based on a Nd:YVO4 crystal and a MgO:PPLN crystal. By aligning the z-axis of the MgO:PPLN crystal to σ- and π-direction of the Nd:YVO4 crystal, the laser can emit green wavelengths at 542 nm and 543 nm, respectively. An optical-to-optical (O-O) efficiency as high as 22% was achieved for the 542 nm green laser, and the maximum O-O efficiency of the 543 nm laser was 35%. To the best of our knowledge, both results are the highest O-O efficiency achieved so far for Nd:YVO4 542 nm and 543 nm green lasers. The long-term power stability of the 542 nm and 543 nm lasers were 0.46%, and 0.19%, respectively.

Capabilities of Autodyne Reception in Medical СО2 Laser Devices

The generation characteristics and the capabilities of autodyne reception in single mode CO 2 lasers with pulse-periodic pumping of the active medium used in medical laser devices are investigated. It has been demonstrated that medical laser device based on CO 2 laser model DIAMOND C-30A (Coherent Сo.) has the best long-term laser power stability ((2–3)%), while the setup with CO 2 laser model 48–2W (Synrad Сo.) has the best short-term stability (0.62%). Amplitude-frequency characteristics of autodyne reception were studied for lasers of these devices. Power spectra of the autodyne signal appearing during evaporation of fat and muscle tissues under CO 2 laser radiation of the three types of laser devices were recorded. It has been shown that all these laser devices allow to detect the autodyne signal during evaporation of biological tissues. The medical laser setup with CO 2 laser model 48–2W has the highest signal-to-noise ratio during detection of laser backscattered radiation. This is due to the fact that this laser has larger autodyne amplification and better short-term power stability. The results can be used in the development of smart laser surgical systems with feedback.

A novel power stability drive system of semiconductor Laser Diode for high-precision measurement

In view of the strict requirements of the current high-precision measurement system for stable output power of the semiconductor LD (Laser Diode), a semiconductor LD stable power drive and multi-closed-loop control system are proposed after analyzing the semiconductor laser’s P–I (Power–Current) characteristics and temperature characteristics. The system uses a microcontroller as the core control unit and realizes the stable power output control of the semiconductor laser by controlling the current, power and temperature parameters. In this system, first, the control structure model of the controlled object has been designed. Second, a controllable closed-loop constant current feedback drive circuit has been designed and a high-precision controllable constant current drive circuit of the semiconductor laser has been obtained. Furthermore, the control circuit has been designed based on the neural PI (Proportional-Integral) control model and realizes the short-term stable power output of the semiconductor LD. Finally, a closed-loop temperature control system is designed to ensure that the operating temperature of the semiconductor laser is relatively stable and a long-term stable power output is obtained. By designing the hardware and software of the control system and conducting long-term experiments in the laboratory, we found that the system can guarantee the output power within 1 W of PD (Proportional-Differential) LD, and its long-term power stability can reach 1%. This system has a certain reference significance in using semiconductor lasers for high-quality detection when there are stringent requirements for power.

125 W single-frequency CW Nd:YVO4 laser based on two-stage dual-end-pumped master-oscillator power amplifiers

We presented a 125 W single-frequency continuous-wave (CW) 1064 nm laser, where a homemade 50.3 W single-frequency CW high quality Nd:YVO4 laser and a two-stage dual-end-pumped master-oscillator power amplifier (MOPA) acted as the seed source and amplifier, respectively. As a result, a maximum output power of 125.2 W was achieved with the incident pump power of 200 W. The optical-to-optical conversion efficiency and the overall amplified power gain were 43.3% and 3.28%, respectively. The measured beam quality M2 and the long-term power stability of the 1064 nm amplifier during 8 h were better than 1.28 and ±0.73%, respectively. Additionally, the power extraction efficiency of the designed MOPA system was further investigated and the results revealed that the key of improvement of the power extraction efficiency of the MOPA system was employing a high-power single-frequency CW laser as the master oscillator.

8.76 W mid-infrared supercontinuum generation in a thulium doped fiber amplifier

Abstract A stable mid-infrared supercontinuum (SC) generation with a maximum average power of 8.76 W in a spectral band of 1.9–2.65 µm is reported. To broaden the bandwidth of SC, a 1.55 µm pulsed laser system delivering 1 ns pulses at a pulse repetition frequency of 500 kHz was used as a seed source for one-stage thulium-doped fiber amplifier. The power conversion efficiency for wavelengths longer than 2.4 µm and 2.5 µm was determined to be 28% and 18%, respectively, which is believed to be the most efficient power distribution towards the mid-infrared in SC sources based on Tm-doped fibers. The power spectral density of the continuum was calculated to be >13 mW/nm with a potential of further scaling-up. A long-term power stability test, showing power fluctuations

Nearly diffraction limited FTIR mapping using an ultrastable broadband femtosecond laser tunable from 133 to 8 µm

Micro-Fourier-transform infrared (FTIR) spectroscopy is a widespread technique that enables broadband measurements of infrared active molecular vibrations at high sensitivity. SiC globars are often applied as light sources in tabletop systems, typically covering a spectral range from about 1 to 20 µm (10 000 – 500 cm−1) in FTIR spectrometers. However, measuring sample areas below 40x40 µm2 requires very long integration times due to their inherently low brilliance. This hampers the detection of ultrasmall samples, such as minute amounts of molecules or single nanoparticles. In this publication we extend the current limits of FTIR spectroscopy in terms of measurable sample areas, detection limit and speed by utilizing a broadband, tabletop laser system with MHz repetition rate and femtosecond pulse duration that covers the spectral region between 1250 – 7520 cm−1 (1.33 – 8 µm). We demonstrate mapping of a 150x150 µm2 sample of 100 nm thick molecule layers at 1430 cm−1 (7 µm) with 10x10 µm2 spatial resolution and a scan speed of 3.5 µm/sec. Compared to a similar globar measurement an order of magnitude lower noise is achieved, due to an excellent long-term wavelength and power stability, as well as an orders of magnitude higher brilliance.

On the Critical Impact of HF Power Drifts for Miniature Helium-Based NMR Gyroscopes

Nuclear magnetic resonance (NMR) gyroscopes constitute a promising technology for miniaturizing navigation-class gyroscopes. We analyze here a configuration based on a mixture of helium-3 and helium-4. We show that frequency shifts due to the circulation of coherence between helium atoms in metastable and fundamental states have a large impact on the gyroscope drift. In order to reach navigation-class, the high-frequency source used to ignite the plasma is required to have a long-term power stability better than ppm.

High-power, high-repetition-rate performance characteristics of β-BaB₂O₄ for single-pass picosecond ultraviolet generation at 266 nm.

We report a systematic study on the performance characteristics of a high-power, high-repetition-rate, picosecond ultraviolet (UV) source at 266 nm based on β-BaB2O4 (BBO). The source, based on single-pass fourth harmonic generation (FHG) of a compact Yb-fiber laser in a two-crystal spatial walk-off compensation scheme, generates up to 2.9 W of average power at 266 nm at a pulse repetition rate of ~80 MHz with a single-pass FHG efficiency of 35% from the green to UV. Detrimental issues such as thermal effects have been studied and confirmed by performing relevant measurements. Angular and temperature acceptance bandwidths in BBO for FHG to 266 nm are experimentally determined, indicating that the effective interaction length is limited by spatial walk-off and thermal gradients under high-power operation. The origin of dynamic color center formation due to two-photon absorption in BBO is investigated by measurements of intensity-dependent transmission at 266 nm. Using a suitable theoretical model, two-photon absorption coefficients as well as the color center densities have been estimated at different temperatures. The measurements show that the two-photon absorption coefficient in BBO at 266 nm is ~3.5 times lower at 200°C compared to that at room temperature. The long-term power stability as well as beam pointing stability is analyzed at different output power levels and focusing conditions. Using cylindrical optics, we have circularized the generated elliptic UV beam to a circularity of >90%. To our knowledge, this is the first time such high average powers and temperature-dependent two-photon absorption measurements at 266 nm are reported at repetition rates as high as ~80 MHz.

Stable low noise 1.5 µm laser generated by a singly resonant optical parametric oscillator

We present a stable low noise continuous wave (CW) single frequency 1.5 µm laser generated by an output-coupled singly resonant optical parametric oscillator based on a periodically poled lithium niobate (PPLN) and a home-made CW single frequency Nd:YVO4 laser at 1.064 µm as the pump source. A maximum signal power of 5.3 W can be obtained at a pump power of 16 W. The long-term power stability is better than ±0.9% in a given two hours and the intensity noise reaches the shot noise limit for frequencies above 3 MHz. The signal wavelength can be tuned from 1.560 to 1.592 µm with PPLN temperature controlled from 120 to 180 °C. This kind of laser source can be used in quantum information processing research.