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Kharenko DS, Gervaziev MD, Kuznetsov AG, Podivilov EV, Wabnitz S, Babin SA. Mode-resolved analysis of pump and Stokes beams in LD-pumped GRIN fiber Raman lasers. OPTICS LETTERS 2022; 47:1222-1225. [PMID: 35230332 DOI: 10.1364/ol.449119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/19/2021] [Accepted: 01/25/2022] [Indexed: 06/14/2023]
Abstract
All-fiber Raman lasers have demonstrated their potential for efficient conversion of highly multimode pump beams into high-quality Stokes beams. However, the modal content of these beams has not yet been investigated. In this work, based on a mode decomposition technique, we are able to reveal the details of intermodal interactions in the different operation regimes of continuous wave multimode graded-index fiber Raman lasers. We observed that, above the laser threshold, the residual pump beam is strongly depleted in its transverse modes with principal quantum number below 10. However, the generated Stokes signal beam mainly consists of the fundamental mode, but higher-order modes are also present, albeit with exponentially decreasing population.
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Sidelnikov OS, Podivilov EV, Fedoruk MP, Kuznetsov AG, Wabnitz S, Babin SA. Mechanism of brightness enhancement in multimode LD-pumped graded-index fiber Raman lasers: numerical modeling. OPTICS EXPRESS 2022; 30:8212-8221. [PMID: 35299567 DOI: 10.1364/oe.449773] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/29/2021] [Accepted: 01/21/2022] [Indexed: 06/14/2023]
Abstract
We develop a comprehensive theory for describing the experimental beam profiles from multimode fiber Raman lasers. We take into account the presence of random linear mode coupling, Kerr beam self-cleaning and intra-cavity spatial filtering. All of these factors play a decisive role in shaping the Stokes beam, which has a predominant fundamental mode content. Although the highly multimode pump beam is strongly depleted, it remains almost insensitive to the different physical effects. As a result, the intensity of the output Stokes beam is an order of magnitude higher than the pump intensity at its maximum, in quantitative agreement with the experimental results and in contrast with the simplified balance model.
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Abstract
Optical parametric oscillators (OPOs) and Raman lasers are two nonlinear-based laser technologies that extend the spectral range of conventional inversion lasers. Power and brightness scaling of lasers are significant for many applications in industry, medicine, and defense. Considerable advances have been made to enhance the power and brightness of inversion lasers. However, research around the power scaling of nonlinear lasers is lacking. This paper reviews the development and progress of output power of continuous-wave (CW) crystalline OPOs and Raman lasers. We further evaluate the power scalability of these two laser technologies by analyzing the cavity architectures and gain materials used in these lasers. This paper also discusses why diamond Raman lasers (DRLs) show tremendous potential as a single laser source for generating exceedingly high output powers and high brightness.
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Spatio-spectral beam control in multimode diode-pumped Raman fibre lasers via intracavity filtering and Kerr cleaning. Sci Rep 2021; 11:21994. [PMID: 34754003 PMCID: PMC8578583 DOI: 10.1038/s41598-021-01491-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2021] [Accepted: 10/22/2021] [Indexed: 12/01/2022] Open
Abstract
Multimode fibres provide a promising platform for boosting the capacity of fibre links and the output power of fibre lasers. The complex spatiotemporal dynamics of multimode beams may be controlled in spatial and temporal domains via the interplay of nonlinear, dispersive and dissipative effects. Raman nonlinearity induces beam cleanup in long graded-index fibres within a laser cavity, even for CW Stokes beams pumped by highly-multimode laser diodes (LDs). This leads to a breakthrough approach for wavelength-agile high-power lasers. However, current understanding of Raman beam cleanup is restricted to a small-signal gain regime, being not applicable to describing realistic laser operation. We solved this challenge by experimentally and theoretically studying pump-to-Stokes beam conversion in a graded-index fibre cavity. We show that random mode coupling, intracavity filtering and Kerr self-cleaning all play a decisive role for the spatio-spectral control of CW Stokes beams. Whereas the depleted LD pump radiation remains insensitive to them.
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Fan C, An Y, Yao T, Xiao H, Huang L, Xu J, Leng J, Zhou P. Seeing the beam cleanup effect in a high-power graded-index-fiber Raman amplifier based on mode decomposition. OPTICS LETTERS 2021; 46:4220-4223. [PMID: 34469978 DOI: 10.1364/ol.433750] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2021] [Accepted: 07/22/2021] [Indexed: 06/13/2023]
Abstract
Due to the beam cleanup effect, brightness enhancement (BE) can be achieved in a Raman fiber amplifier (RFA) based on multimode (MM) graded-index (GRIN) fiber. In this Letter, a novel, to the best of our knowledge, diagnostic tool of mode decomposition (MD) based on a stochastic parallel gradient descent algorithm is demonstrated to observe the beam cleanup effect in a GRIN-fiber-based RFA for the first time, to our knowledge. During output power boosting up to 405 W at 1130 nm, the output beam quality factor M2 improves from 3.45 to 2.88, with a BE factor of 10.5. The MD results based on the near-field beam profiles from RFA indicate that the modal weight of the fundamental mode increases from 74.5% to 87%, confirming that the fundamental mode dominates with higher Raman gain. Moreover, the beam quality is found to be limited by the existence of a higher-order (Laguerre-Gaussian) LG10 mode, which is insensitive to the beam cleanup effect. The correlation coefficient reaches over 0.98 for all MD results. Thus, the accuracy of the MD method is high enough to provide further valuable insight into the physics of spatiotemporal beam dynamics in MM GRIN fiber.
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Fan C, Chen Y, Yao T, Xiao H, Xu J, Leng J, Zhou P, Wolf AA, Nemov IN, Kuznetsov AG, Kablukov SI, Babin SA. Over 400 W graded-index fiber Raman laser with brightness enhancement. OPTICS EXPRESS 2021; 29:19441-19449. [PMID: 34266053 DOI: 10.1364/oe.427605] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2021] [Accepted: 06/01/2021] [Indexed: 06/13/2023]
Abstract
The power scaling on all-fiberized Raman fiber oscillator with brightness enhancement (BE) based on multimode graded-index (GRIN) fiber is demonstrated. Thanks to beam cleanup of GRIN fiber itself and single-mode selection properties of the fiber Bragg gratings inscribed in the center of GRIN fiber, the efficient BE is realized. For the laser cavity with single OC FBG, continuous-wave power of 334 W with an M2 value of 2.8 and BE value of 5.6 were obtained at a wavelength of 1120 nm with an optical-to-optical efficiency of 49.6%. Furthermore, the cavity reflectivity is increased by employing two OC FBGs to scale the output power up to 443 W, while the corresponding M2 is 3.5 with BE of 4.2. To our best knowledge, it is the highest power in Raman oscillator based on GRIN fiber.
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Zhu S, Feng Y, Barua P, Nilsson J. Efficient low-brightness-pumped Raman amplification of a single high-order Bessel mode in 335-m of 70-µm-diameter silica-core step-index fiber. OPTICS LETTERS 2020; 45:6018-6021. [PMID: 33137058 DOI: 10.1364/ol.404602] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/07/2020] [Accepted: 09/24/2020] [Indexed: 06/11/2023]
Abstract
We experimentally demonstrate Raman amplification of signal pulses in a high-order Bessel mode (LP06) at a wavelength of 1121 nm in a 335-m step-index fiber with a 70-µm diameter, 0.227-NA pure-silica core. This was pumped by 5-ns multimode pulses at 1065 nm from a Yb-doped fiber master oscillation power amplifier. The mode purity of the amplified pulses is well preserved to 23 dB of average-power gain, to 774 W of peak power in 2 ns pulses at a 20 kHz repetition rate, when pumped with a peak power of 942 W. The pump depletion as averaged over the signal pulses reaches 59%. We believe, to the best of our knowledge, that this is the first demonstration of stable mode propagation and Raman amplification of a single Bessel-like higher-order mode in a fiber of hundreds of meters. This shows the potential for efficient power scaling of a single signal mode with low-brightness pumping, comparable with that from continuous-wave multimode diode lasers.
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Chen Y, Yao T, Huang L, Xiao H, Leng J, Zhou P. 2 kW high-efficiency Raman fiber amplifier based on passive fiber with dynamic analysis on beam cleanup and fluctuation. OPTICS EXPRESS 2020; 28:3495-3504. [PMID: 32122016 DOI: 10.1364/oe.383683] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/25/2019] [Accepted: 01/15/2020] [Indexed: 06/10/2023]
Abstract
In this paper, we study the power scaling in high power continuous-wave Raman fiber amplifier employing graded-index passive fiber. The maximum output power reaches 2.087 kW at 1130 nm with an optical conversion efficiency of 90.1% (the output signal power versus the depleted pump power). To the best of our knowledge, this is the highest power in the fields of Raman fiber lasers based merely on Stokes radiation. The beam quality parameter M2 improves from 15 to 8.9 during the power boosting process, then beam spot distortion appears at high power level. This is the first observation and analysis on erratic dynamic properties of the transverse modes in high power Raman fiber amplifier.
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Kuznetsov AG, Evmenova EA, Dontsova EI, Kablukov SI, Babin SA. Frequency doubling of multimode diode-pumped GRIN-fiber Raman lasers. OPTICS EXPRESS 2019; 27:34760-34768. [PMID: 31878659 DOI: 10.1364/oe.27.034760] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/05/2019] [Accepted: 10/16/2019] [Indexed: 06/10/2023]
Abstract
Frequency doubling of multimode diode-pumped GRIN-fiber Raman laser with improved beam quality (M2=1.9-2.6 depending on configuration) in a simple single-pass scheme with 5-mm PPLN crystal is studied. After scheme optimization and elimination of back reflection and crystal heating effects, an efficient conversion into blue spectral range with output power of about 0.4 W@488 nm and 0.64 W@477 nm has been demonstrated.
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Evmenova EA, Kuznetsov AG, Nemov IN, Wolf AA, Dostovalov AV, Kablukov SI, Babin SA. 2nd-order random lasing in a multimode diode-pumped graded-index fiber. Sci Rep 2018; 8:17495. [PMID: 30504776 PMCID: PMC6269461 DOI: 10.1038/s41598-018-35767-9] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2018] [Accepted: 11/09/2018] [Indexed: 11/09/2022] Open
Abstract
Raman lasing in a graded-index fiber (GIF) attracts now great deal of attention due to the opportunity to convert high-power multimode laser diode radiation into the Stokes wave with beam quality improvement based on the Raman clean-up effect. Here we report on the cascaded Raman generation of the 2nd Stokes order in the 1.1-km long GIF with 100-μm core directly pumped by 915-nm diodes. In the studied all-fiber scheme, the 1st Stokes order is generated at 950-954 nm in a linear cavity formed at GIF ends by two fiber Bragg gratings (FBGs) securing beam quality improvement from M2 ≈ 30 to M2 ≈ 2.3 due to special transverse structure of FBGs. The 2nd Stokes wave is generated either in linear (two FBGs) or half-open (one FBG) cavity with random distributed feedback via Rayleigh backscattering. Their comparison shows that the random lasing provides better beam quality and higher slope efficiency. Nearly diffraction limited beam (M2 ≈ 1.6) with power up to 27 W at maximum gain (996 nm), and 17 W at the detuned wavelength of 978 nm has been obtained, thus demonstrating that the 2nd-order random lasing in diode-pumped GIF with FBGs provides high-efficiency high-quality beam generation in a broad wavelength range within the Raman gain spectral profile.
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Affiliation(s)
| | - Alexey G Kuznetsov
- Institute of Automation and Electrometry SB RAS, Novosibirsk, 630090, Russia
| | - Ilya N Nemov
- Institute of Automation and Electrometry SB RAS, Novosibirsk, 630090, Russia
| | - Alexey A Wolf
- Institute of Automation and Electrometry SB RAS, Novosibirsk, 630090, Russia
- Novosibirsk State University, Novosibirsk, 630090, Russia
| | - Alexandr V Dostovalov
- Institute of Automation and Electrometry SB RAS, Novosibirsk, 630090, Russia
- Novosibirsk State University, Novosibirsk, 630090, Russia
| | - Sergey I Kablukov
- Institute of Automation and Electrometry SB RAS, Novosibirsk, 630090, Russia
- Novosibirsk State University, Novosibirsk, 630090, Russia
| | - Sergey A Babin
- Institute of Automation and Electrometry SB RAS, Novosibirsk, 630090, Russia.
- Novosibirsk State University, Novosibirsk, 630090, Russia.
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Glick Y, Shamir Y, Aviel M, Sintov Y, Goldring S, Shafir N, Pearl S. 1.2 kW clad pumped Raman all-passive-fiber laser with brightness enhancement. OPTICS LETTERS 2018; 43:4755-4758. [PMID: 30272732 DOI: 10.1364/ol.43.004755] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/10/2018] [Accepted: 08/29/2018] [Indexed: 06/08/2023]
Abstract
An all-fiber clad pumped Raman fiber laser (FL) oscillator with a CW power of 1.2 kW and an efficiency of 85% is presented. To the best of our knowledge, this laser is the highest power and the highest efficiency Raman FL demonstrated in any configuration with brightness enhancement (BE). To the best of our knowledge, it is also the first greater than kilowatt FL of any kind that does not utilize rare-earth doping in the oscillator fiber (all passive fiber). The beam quality (BQ) of the Raman laser was M2=2.75 at 1 kW, and the pump-Stokes BE factor was approximately 7. The laser consists of a specially designed triple-clad fiber which confines the low BQ pump power into the multi-mode inner clad, while generating the Raman signal in the large-mode-area core. The second Stokes is inhibited by selecting the appropriate inner clad-to-core area ratio and by the oscillator's selective fiber Bragg grating reflectors.
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Bai Z, Williams RJ, Kitzler O, Sarang S, Spence DJ, Mildren RP. 302 W quasi-continuous cascaded diamond Raman laser at 1.5 microns with large brightness enhancement. OPTICS EXPRESS 2018; 26:19797-19803. [PMID: 30119299 DOI: 10.1364/oe.26.019797] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/18/2018] [Accepted: 05/25/2018] [Indexed: 06/08/2023]
Abstract
We report a second Stokes diamond Raman laser at 1.49 μm capable of high power and large-scale-factor brightness enhancement. Using a quasi-continuous 1.06 μm pump of power 823 W (0.85% duty cycle) and M2 up to 6.4, a maximum output power of 302 W was obtained with an M2 = 1.1 providing an overall brightness enhancement factor of 6.0. The pulse length of ~210 μs was selected to ensure operation was representative of steady-state continuous lasing conditions in the diamond bulk. Accompanying theoretical calculations indicate that even more strongly aberrated pumps may be used to efficiently generate high beam quality output and with higher brightness enhancement factors. This diamond-based beam conversion technique addresses needs for high brightness and efficient eye-safe sources using low-brightness 1 μm pumps and reveals a widely-applicable route to practical high brightness lasers of increased wavelength range.
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Glick Y, Shamir Y, Wolf AA, Dostovalov AV, Babin SA, Pearl S. Highly efficient all-fiber continuous-wave Raman graded-index fiber laser pumped by a fiber laser. OPTICS LETTERS 2018; 43:1027-1030. [PMID: 29489772 DOI: 10.1364/ol.43.001027] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/29/2017] [Accepted: 01/24/2018] [Indexed: 06/08/2023]
Abstract
We report for the first time, to the best of our knowledge, an all-fiber Raman graded-index (GRIN) fiber laser pumped by a fiber laser. This configuration points to potential future power and brightness increases. Continuous-wave power of 135 W with an M2 value of 2.5 was obtained at a wavelength of 1081 nm with an optical-to-optical efficiency of 68%. A commercial GRIN core fiber acts as the Raman fiber in a power oscillator configuration that includes fiber Bragg gratings (FBGs) written onto the GRIN fiber. The efficiency and brightness demonstrated here are, to the best of our knowledge, the highest reported in any Raman GRIN fiber laser. A brightness enhancement of the pump beam by a factor of 5.6 is attained due to the transverse profiles of Raman gain and FBG reflection in the GRIN fiber.
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Shamir Y, Glick Y, Aviel M, Attias A, Pearl S. 250 W clad pumped Raman all-fiber laser with brightness enhancement. OPTICS LETTERS 2018; 43:711-714. [PMID: 29444059 DOI: 10.1364/ol.43.000711] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/25/2017] [Accepted: 12/20/2017] [Indexed: 06/08/2023]
Abstract
We report a strictly all-fiber clad pumped Raman fiber laser with a CW power of 250 W. To the best of our knowledge, this is the highest power Raman fiber laser demonstrated in any configuration allowing brightness enhancement. In addition, this is the first report of a Raman clad pumped all-fiber laser. The brightness of the pump source was enhanced by a factor of ∼3.8. This result was achieved by the design of a novel triple-clad fiber, with tight pump power inner confining clad that both maximized the Raman gain and inhibited the second Stokes radiation. We discuss power-increase effects on the beam quality, efficiency, and brightness enhancement.
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Bai Z, Williams RJ, Jasbeer H, Sarang S, Kitzler O, Mckay A, Mildren RP. Large brightness enhancement for quasi-continuous beams by diamond Raman laser conversion. OPTICS LETTERS 2018; 43:563-566. [PMID: 29400841 DOI: 10.1364/ol.43.000563] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2017] [Accepted: 12/21/2017] [Indexed: 06/07/2023]
Abstract
High average power lasers with high beam quality are critical for emerging applications in industry and research for defense, materials processing, and space applications. However, overcoming thermal effects in the gain medium remains the key challenge for increasing laser brightness at high powers. Here we report a means for increasing the beam brightness of high-power continuous-wave (CW) beams based on external cavity Raman lasers using diamond, a material with thermal properties far superior to any other laser material. With pump beam quality in the range M2=2.3-7.3, efficient pump-limited conversion to an M2=1.1 Stokes beam is achieved in all cases, with increases in brightness from the pump by factors as high as 12.7. The influence of pump beam quality on laser threshold and slope efficiency is analyzed. This Letter foreshadows an alternative approach for scaling the brightness of CW lasers using high-power, moderate beam quality pumps up to M2=20 or more, such as thin-disk and slab lasers and fiber lasers operating in a mode instability regime.
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Zlobina EA, Kablukov SI, Wolf AA, Nemov IN, Dostovalov AV, Tyrtyshnyy VA, Myasnikov DV, Babin SA. Generating high-quality beam in a multimode LD-pumped all-fiber Raman laser. OPTICS EXPRESS 2017; 25:12581-12587. [PMID: 28786613 DOI: 10.1364/oe.25.012581] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/10/2017] [Accepted: 05/06/2017] [Indexed: 06/07/2023]
Abstract
We report on the first demonstration of an all-fiber CW Raman laser based on a multimode graded-index fiber directly pumped by multimode fiber-coupled laser diodes. A joint action of Raman clean-up effect and mode-selection properties of special fiber Bragg gratings inscribed in the central part of the graded-index fiber core, results in high-efficiency conversion of a multimode (M2~26) pump at 915 nm into a high-quality (M2~2.6) output beam at 954 nm. About 50 W output power has been obtained with slope efficiency of 67%. The proposed development and integration of key multimode fiber technologies opens the door to new type of LD-pumped high-power high-beam-quality fiber lasers that may operate at almost any wavelength defined by available LDs.
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Zlobina EA, Kablukov SI, Wolf AA, Dostovalov AV, Babin SA. Nearly single-mode Raman lasing at 954 nm in a graded-index fiber directly pumped by a multimode laser diode. OPTICS LETTERS 2017; 42:9-12. [PMID: 28059211 DOI: 10.1364/ol.42.000009] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
High beam quality and narrow spectrum have been obtained in a Raman fiber laser based on a 1.1 km long graded-index fiber directly pumped by a multimode 915 nm laser diode. The generation of a near-diffraction-limited beam at 954 nm with M2≤1.27 and Δλ=0.42 nm at an output power above 10 W is enabled by a cavity mirror made of a special fiber Bragg grating inscribed by a femtosecond technique in the central part of the graded-index fiber core.
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