A multi-laser comb light source that uses an optical reference scheme to mutually stabilize laser combs according to an internal optical reference.

Abstract

A multi-laser-based comb (MLC) light source is composed of multiple laser combs. The MLC is further composed of a narrow-linewidth optical pump containing a single-frequency laser common to the laser combs. Pump light from the narrow-linewidth optical pump is coupled to the laser combs, exciting them and outputting their respective frequency combs, each spanning one or more octaves. Each laser comb is phase-locked to the SF laser of the optical pump, thereby providing high mutual coherence to the laser combs.

Description

Technical Field

[0001] The present disclosure generally relates to optical frequency comb generation. In particular, the present disclosure relates to a multi laser-based comb (MLC) light source that provides high mutual phase coherence and stabilization transfer between the frequency combs of this light source by phase-locking a reference scheme to a narrow-linewidth optical pump common to each of the laser combs.

Background Art

[0002] Broadband frequency combs have attracted particular attention because they enable a number of important applications related to the study of complex molecular systems and non-invasive diagnostics. One well-established approach for generating frequency combs is based on Kerr mode-locked (KLM) ultrafast light sources, i.e., high-power pulsed lasers excited by respective pumps. These light sources enable, for example, the direct generation and amplification of ultrashort fs pulses in a desired spectral range, such as in the mid-infrared (MIR) spectral range (2 μm to 20 μm), at a fixed pulse repetition frequency (PRF) f ,

[0003] In. KLM light sources are based on polycrystalline bulk materials selected from TM:II-VI groups, including crystals of, for example, chromium-doped zinc sulfide and zinc selenide (Cr:ZnS and Cr:ZnSe respectively). The latter are disclosed in U.S. Patent No. 10,483,709, U.S. Patent No. 10,216,063, and U.S. Patent No. 10,886,690, which are incorporated herein by reference in their entirety.

[0003] In its basic form, the exemplary KLM light source contains a bulk material such as a Cr:ZnS crystal and generates an optical frequency comb by inducing cross-phase modulation (XPM) between a femtosecond (fs) pulse train copropagating through the crystal and a CW pump laser beam. The latter generates an output containing an infinite number of period fs pulses at the fundamental frequency f and its harmonics via a random quasi-phase matching (RQPM) process within the bulk. Performing a Fourier transform on each of these pulses yields a continuous ultrabroadband spectrum or supercontinuum, represented by equidistant lines corresponding to mutually coherent fundamental and harmonic frequency combs. Two degrees of freedom are associated with the frequency comb. The spacing between adjacent frequencies is directly defined by the pulse repetition frequency (PRF) of the laser comb. The other degree of freedom is the slip ratio of the carrier envelope offset (CEO) from pulse to pulse.

[0004] Referring to Figure 1(1A), the interval between adjacent frequencies is PRF f rep It is equal to. In the time domain, adjacent pulses are T=1 / f rep They are uniformly separated from each other. To stabilize the PRF, the frequency laser comb must be mode / phase synchronized, which means that the longitudinal modes of the laser's resonant cavity are in a fixed phase relationship, resulting in constructive interference between these modes that cause ultrashort pulse trains. One PRF control technique utilizes a phase-locked loop (PLL) to adjust the length of the laser cavity.

[0005] The pulse inhomogeneity shown in Figure 1(1A) is a result of chromatic and nonlinearity within the laser cavity, which is the CEO f from pulse to pulse. ceo This causes slippage. This slippage occurs because the group velocity and phase velocity within the laser cavity differ slightly from pulse to pulse. To control this slippage, the PLL adjusts the pump power to keep the CEO at a defined setpoint.

[0006] When both the PRF and CEO are stable, the Fourier transform of the output pulse yields a sharp radio frequency (RF) spectrum or optical frequency comb, as can be seen in Figure 1(1B). In summary, if the PRF and CEO are known, all the frequencies of the output are known, and the output frequency comb is used as an "optical ruler."

[0007] The operation of MLC light sources enables high-speed measurements with a wide spectral range and high resolution (~0.1 GHz), which requires a high mutual coherence time (on the order of several seconds) between its laser combs. Mutual coherence occurs when the two laser combs are phase-locked, that is, when the phase of one follows the phase of the other. Without this, adjacent teeth of the output frequency combs will blend together, sacrificing several orders of magnitude of spectral resolution and reducing the accuracy of both frequency and amplitude that is possible with this technique.

[0008] Referring to Figure 2, it can be seen that MLC light sources have a wide range of applications in various industries, including, for example, the MIR dual-comb spectroscopy (DCS) diagram shown in Figure 2. Known high-end MLC light sources with high mutual coherence times rely on the laser comb referencing an external narrowband continuous-wave (CW) etalon laser. The etalon laser provides a reference for obtaining coherence between optical signals because it operates at the high optical frequencies required that cannot be obtained by electronics. While this approach yields excellent results, it complicates the structure, significantly increases costs, and requires close operating wavelengths for each frequency laser comb.

[0009] Therefore, there is a need for an MLC light source with a reference scheme to achieve a high degree of mutual phase coherence between two or more laser combs without using an external etalon laser. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] U.S. Patent No. 10,483,709 [Patent Document 2] U.S. Patent No. 10,216,063 [Patent Document 3] U.S. Patent No. 10,886,690 [Overview of the Initiative] [Problems that the invention aims to solve]

[0011] The disclosed MLC light source, which includes two or more frequency laser combs, is based on a reference scheme that includes a narrow-linewidth pump that excites the laser combs and simultaneously provides an internal reference for phase-locking each of these lasers. Since each laser comb is phase-locked to the same internal reference, they have very high mutual coherence and eliminate the need for an external laser / reference in known devices.

[0012] Structurally, the two or more disclosed laser combs output each a series of ultrashort pulses, each having a supercontinuum of ultra-broadband single-octave—multi-octave length (and longer) output frequency combs. The laser combs are excited by narrow-linewidth laser pumps, and each laser is phase-locked to a pump that gives the laser combs high mutual coherence. [Means for solving the problem]

[0013] According to one characteristic of MC light sources, mode-locked laser combs have a master oscillator (MO) power amplifier / supercontinuum generator (PA SCG) architecture, each including a master oscillator and a power amplifier. Alternatively, a suitable high-power SF pulsed laser can replace the MOPA configuration of the laser comb.

[0014] According to another disclosed feature of the MC light source, both the MO and PA SCG of each laser comb are selected from the TM:II-VI family. For example, both the MO and PA of each SC laser are either Cr:ZnS or Cr:ZnSe, or one of the MO and PA is Cr:ZnS and the other is Cr:ZnSe.

[0015] The PA SCG of each laser comb is excited by narrow-linewidth pump light of sufficient intensity to initiate nonlinear effects in the PA SCG that govern the propagation of the fs pulse through this amplifier. The nonlinear effects include intrapulse three-wave mixing due to RQPM, self-phase modulation (SPM) resulting in a spectral broadening of the pulse spectrum to more than one octave, and cross-phase modulation (XPM) between the PA SCG (ωi,comb) and the narrow-linewidth pump (ωp), forming a new comb such that ωk,p = ωp + ωi,comb - ωj,comb, (k = ij). As a result, the output spectrum of each laser comb includes the pump frequency comb, the second harmonic (SH) frequency comb (2f), and an amplified fundamental frequency comb (f) superimposed with sum frequency generation (SFG) involving the third 3f, fourth 4f, and higher frequency combs, respectively.

[0016] According to another feature of the light source of the present invention, the narrow-linewidth pump includes an SF CW laser. A single SF CW laser may be coupled to multiple pump amplifiers that simultaneously excite their respective SC lasers. The SF CW laser is selected from SF solid-state lasers, including SF semiconductor, SF fiber lasers, or SF diode-pumped bulk lasers, operating within a desired frequency range such as the MIR spectral region, and may have a Fabry-Perot or ring resonator configuration. The pump amplifier may be selected from solid-state or fiber amplifiers.

[0017] One structural possibility is to have a single pump amplifier that excites both the MO and PA of each com laser. Yet another possibility is to have two pump amplifiers that excite the respective MO and PA of each laser com. Regardless of the number of pump amplifiers, they are all seeded by the same SF CW pump laser.

[0018] Alternatively, the pump may only include an SF laser that outputs pump light directly coupled to a plurality of SC lasers. Clearly, the SF CW laser must be configured to output sufficient power to assist in the generation of an octave-spanning frequency comb. Currently, fiber and bulk SF CW lasers are reported to output up to 1 KW.

[0019] The output of each laser com is incident on a frequency discriminator, such as a dichroic mirror, which separates some of the combs from the remaining harmonic combs that exit from one or the specified light source outputs. The filtered frequency comb is further guided through two different PLLs for each laser com, and its operation is well known to those skilled in the art of mode-locked laser technology.

[0020] The narrow-linewidth pump does not necessarily have to be based on an SF CW laser, regardless of the presence or absence of a pump amplifier. It can be configured as a pulsed device that should operate as a laser com generating an fs frequency comb.

[0021] Specifically, one of the PLLs operates based on the detected phase difference between the two SC lasers. This includes a phase frequency detector (PFD) and provides a beat note signal that is applied to an actuator that adjusts the length of the resonant cavity of the MO corresponding to the phase adjustment between the laser com and the pump. Since the frequency mode spacing of the fs frequency comb is equal to the reciprocal of the cavity round-trip time, the PRF is corrected indirectly by adjusting the phase. The other PLL controls the CEO. It is configured similarly to the above PLL, but the control signal modulates the pump power.

[0022] Additional other features are described in detail below. Further, both the foregoing information and the following detailed description are merely exemplary examples of various aspects and features showing that the particular features, structures, or characteristics described may be included with at least one or all of the disclosed features.

[0023] Various aspects of the present disclosure are described below with reference to the accompanying drawings, which are not intended to be drawn to scale. The figures are included to provide an illustration of various features and further understanding, and are incorporated herein and constitute a part of this specification, but are not intended as a definition of the limitations of the particular embodiments. The descriptions of the figures are shown below.

Brief Description of the Drawings

[0024] [Figure 1] Figs. (1A, 1B) are diagrams illustrating the known operating principle of a mode-locked laser. [Figure 2] It is a highly schematic diagram of a known MLC of the prior art. [Figure 3] It is a schematic diagram of one of the optical systems of the laser comb of the MLC of the present invention. [Figure 4] Fig. (4A) shows the electric field of the pulse signal at the inner focus of the PA of the laser comb of Fig. 3, and Fig. (4B) illustrates the electric field of the SF CW pump signal. [Figure 5AB] Figs. (5A, 5B) are diagrams of the normalized spectral distributions of the respective pulses and CW pump signals at the inner focus of the PA of the laser comb of Fig. 3. [Figure 5C] It is a diagram showing pump combs generated in each supercontinuum generator (PA SCG) of the laser comb of the disclosed light source. [Figure 6] It is a diagram of the RF spectrum of the interference of the pump and SH frequency combs detected by the PD. [Figure 7] Figs. (7A, 7B) are diagrams of the respectively zoomed-in spectral regions of the pump and SH combs of the spectrum of Fig. 6. [Modes for carrying out the invention]

[0025] The following description focuses on an MLC light source configured with a phase-referenced scheme that is operable to provide a high degree of mutual coherence and stable transfer between multiple laser combs. The optical referenced scheme is based on phase-locking techniques to phase-lock each of the multiple laser combs to an internal narrow CW pump of the light source, which is common to all laser combs. As a result, the disclosed MLC light source features high mutual coherence (on the order of tens of seconds), stable transfer between two or more laser combs, and simplified structural complexity and cost associated with known MC setups.

[0026] Referring to Figure 3, the MC light source 10 of the present invention is configured using two or more laser combs 12—each a multi-octave frequency comb outputting an ultrashort pulse laser—each extending from the bandgap edge of the comb-generating nonlinear material to its phonon cutoff. Although only one of the laser combs 12 is shown, the rest of the laser combs are all configured in the same way as shown and are excited by the narrow-linewidth pumps 14 of the shown laser combs. As illustrated, the laser combs 12 have an MOPA architecture with an MO 16 and a PA supercontinuum generator (PA SCG) 18, both of which are based on, for example, polycrystalline Cr:ZnS. The MO 16 may have a single-pass or multi-pass resonant cavity. The illustrated MO 16 is a 3-cycle (24fs) oscillator.

[0027] Each laser comb 12 is phase-locked to the same reference—narrow-linewidth pump 14—which provides stable transfer between each laser comb 12 and pump 14 while giving the laser combs 12 high cross-phase coherence. Since the laser combs 12 output their respective frequency combs across multiple octaves, pump 14 can operate at any wavelength in the range of 0.35 nm to approximately 12 μm. In the illustrative schematic diagram shown, the SF CW pump laser 20 operates in the C band, somewhat between 1530 and 1565 nm, corresponding to the amplification range of the erbium (Er)-doped pump amplifier 18 that boosts the 5 mW output of laser 16 to several watts (W). As shown in Figure 3, the 5 mW SF pump light is amplified to 7 W light coupled to MO 16 and 10 W light that excites PA SCG 18.

[0028] The narrow-linewidth pump 14 necessarily includes an SF device, such as an SF CW laser 20, and may also have at least one amplifier 22. The remaining laser combs 12, not shown, are each directly coupled to the illustrated SF pump laser 20 and thus act as etalon lasers / references. The SF CW pump laser 20 may be selected from a diode laser, bulk laser, or fiber laser, while the pump amplifier 22 is preferably either a fiber or bulk amplifier doped with any of the known photogenerating ions.

[0029] When pump amplifiers are used, as illustrated, the SF CW laser 20 seeds two Er-doped fiber pump amplifiers (EDFLs) 22 to excite the respective MO 12, 16 and PA SCG 18 of the laser combs 12. Importantly, each laser comb 12 is provided with a pair of pump amplifiers 22 so that the SF CW pump laser 20 also seeds the pump amplifiers 22 of each additional laser comb 12. One obvious modification of the pump 14 involves using a single pump amplifier 22 for each laser comb 12. Another modification of the pump scheme may involve the illustrated narrow-linewidth pump 14, which is used overall to excite all the laser combs 12. In the latter modification, the pump amplifiers 22 may be unnecessary if the SF CW laser 20 meets the power and other requirements. In summary, the only non-negotiable condition that the narrow-linewidth pump 14 must meet is the use of an SF CW laser, which is the SF CW pump laser 20 in the illustrated example.

[0030] Referring again to the power conditions for the narrow-linewidth pump 14, the pump beam should have enough power to trigger the onset of a nonlinear effect (NLE) at least in the PA SCG 18, but possibly in both the MO 16 of the laser comb 12 and the PA SCG 18. In the schematic diagram shown, the intensity threshold for NLE is approximately 20 GW / cm². 2 ~40 GW / cm² 2This can be within the illustrative range. Several nonlinear effects dominate the propagation of the fs pulse through the PA-SCG stage, optical rectification (0f) which increases the fundamental wavelength, intrapulse three-wave mixing due to RQPM, self-phase modulation (SPM) which results in a spectral broadening of the pulse spectrum into one octave, and cross-phase modulation (XPM) between the Cr:ZnS comb (ωi,comb) and the narrow-linewidth pump (ωp). The latter forms a new comb called the pump-frequency comb (p-comb), where each tooth may be numbered as ωk,p=ωp+ωi,comb-ωj,comb, (k=ij) with i and j as integers. Thus, the output of the PA-SCG18 illustrated in Figure 5A includes an amplified fundamental-frequency comb (f) superimposed on a secondary-frequency comb. The latter are generated by different nonlinear processes, such as optical rectification (0f), second HG (2f), SFG (3f, 4f, etc.), and, importantly, p-combs generated via XPM. In the schematic diagram of the example shown, fR = 80 MHz, and the mode spacing of all frequency combs is defined by the PRF of the MO. The CEO offset frequency of the p-comb is f0P = rem(2πωP, fR), where ωP is the pump laser frequency, which is 191 THz in the example shown.

[0031] When Figure 3 is considered in combination with Figures 4(4A) and 5A, in the process disclosed above the exemplary schematic diagram of multi-octave frequency comb generation in Figure 3, MO16 generates input fs pulses 32, each centered on a fundamental f frequency of 125 THz. Figure 4(4A) shows the time distribution of the pulse signals, which result from the superposition of 0f, f, and 2f-h frequency combs, as well as higher-order harmonic combs, at the inner focus of PA SCG18, and correspond to the highest instantaneous intensity when the input pulses 32 are coupled to PA SCG18. Co-propagating with the pump light along PA SCG18, the spectrum of the input pulses 32 within PA SCG18 begins to broaden due to the NLE disclosed above, eventually transforming into the output pulses 34, which are better seen in Figure 4(4A). It is readily apparent from Figures 3 and 5A that the fundamental f frequency comb of the output pulse 34 is not only broader than that of the input pulses 32, but also includes the pump p-comb 38 and SH 2f comb 36 generated in PA SCG18. Furthermore, the output pulse 34 includes the rectified frequency comb 0f, as well as the third and fourth harmonic combs 3f and 4f, all generated within the PA SCG18 in Figure 3, along with any other possible higher-order harmonic combs.

[0032] Referring again to the narrow-linewidth pump 14, it will be readily apparent to those skilled in the art in the field of laser technology that the CW operating region of the pump 14 is not the only region in which the pump can operate within the context of the disclosed light source 10. The pump 14 can also operate in the pulsed region and output a series of fs pulses, i.e., it can output another laser comb in addition to the laser comb 12. One condition that must be satisfied in the case of the pump-laser comb is that it must be proven that this comb has the necessary temporal stability to obtain a beat note signal. The latter refers to the phase difference that occurs during the operation of the light source 10 between the pump and the other laser comb due to interference between the pump and the selected frequency comb, as disclosed below. Yet another condition concerns the crystal amplifier PA SCG 18—these must be very good at withstanding high light intensities.

[0033] Figures 4(4B) and 5B illustrate the p-comb 38 captured in spectral zone 40 of Figure 5A, where the fundamental frequency and SH combs 34 and 36 merge, respectively. Zone 40 is selected for measurements after the CEO frequency, but in addition, this zone is of interest because it contains the p-comb 38. As shown in Figure 5C, PA SCCG 18 receives the near-IR narrowband spectrum of the SF CW input 42 (Figure 5B) and generates the p-comb 38 containing the IR narrowband component.

[0034] The light guide optical system of the MC light source 10 can have various configurations. As shown in the figure, the MO 16 and PA SCG 18 are optically connected through a first dichroic mirror (DM) 28 that transmits the output coupler 24 of the MO resonant cavity, a reflector 26, and pump light, but deflects the seed light from the MO 16 so that the pump and MO outputs copropage before coupling to the PA SCG 18.

[0035] The output frequency comb of laser comb 12 is incident on another DM28 that separates the near-infrared portion of the output from the fundamental frequency comb. This near-infrared portion includes a narrowband pump component (≈4W), i.e., the SF of pump laser 20, the p-comb generated by the PA SCG 18 of laser comb 12, the SHG 2f comb (0.3W), and the shortwave portion of the fundamental frequency f-comb. The narrowband pump component is then attenuated by a notch filter 46 to ensure the fidelity of the signal measured by PD30—an InGaAs photodiode. A bandpass filter 48 filters the optical signal into the 1.55 μm band, and the fp-2f optical signal, including the overlapping comb at the output of the bandpass filter, is detected by PD30. The latter generates an RF signal with the RF spectrum shown in Figure 6. The RF spectrum reveals the beat between the fundamental f-comb and the SHG 2f-comb at offset frequency f0, as well as the beat between both the f and 2f combs relative to the p-comb at beat frequency fb. Thus, the output RF signal from PD30 includes two RF frequency components f0 and fb, which are further used to adjust the CEO frequency and its phase, respectively, of the laser comb 12.

[0036] The output signal from PD30 is then split into two paths defined by each PLL. The underlying mechanism of the PLL operates based on the phase difference between the two signals. In the illustrative schematic diagram, both PLLs have exactly the same configuration. Each PLL includes a phase frequency detector (PFD) 48 with two inputs, one input for the fb or f0 component and the other input for a reference signal, which in the illustrated schematic diagram is a stable signal from a rubidium (Rb) clock 56. In comparison, two control signals are generated by each PFD 48 when necessary. Another structural component of each PLL is a servo amplifier 50. One of the controlled-amplified signals is coupled to an acousto-optic modulator (AOM) 52, which modulates the pump power, thereby adjusting the CEO frequency. The other LLP, which measures the relative phase relationship between the narrow-linewidth pump 14 and the laser comb 12, delivers the other control signal to the piezoelectric actuator 54. The latter adjusts the length of the resonator of the laser comb 12, thereby phase-synchronizing the laser comb 12 with the pump 14 and adjusting the PRF of the MO 16.

[0037] Figures 7A and 7B show the respective RF spectra of the phase-locked f0 and fb signals measured in the in-loop. While the XPM effect can be observed in a wide variety of materials, these figures show that this effect is sufficient to generate a detectable signal corresponding to the pump p-comb that substantially matches the signal intensity corresponding to the SH comb 36. In the exemplary schematic diagram of Figure 3, both the SH and pump output frequencies are within the 1 μm range, which facilitates the detection and measurement of the p-comb. In other words, the experimental results shown in these figures definitively demonstrate that the optical power of the p-comb is high enough to control each phase-locked process of the laser comb 12 to the narrow-linewidth pump 14.

[0038] While several features of the disclosed light sources have been described in this manner, it will be understood that various modifications, alterations, and improvements are readily conceivable to those skilled in the art. For example, the materials and wavelengths used herein for the laser combs can be substituted with other known materials used in the generation of frequency combs. Such modifications, alterations, and improvements are intended to be part of this disclosure and within the scope of the examples described herein. Accordingly, the foregoing description and drawings are merely illustrative.

[0039] The claims are as follows: [Explanation of symbols]

[0040] 10 MC light source 12 Lasercomb 14 Narrow Wire Width Pump 16 MO 18 PA Supercontinuum Generator (PA SCG) 20 SF CW Pump Laser 22 Amplifiers 24 Output Coupler 26 Reflector 28. First Dichroic Mirror (DM) 30 PD 32 input fs pulses 34 output pulses 36 SH 2f Com 38 Pump P-Comb 40 spectral zones 42 SF CW input 46 Notch Filter 48 PFD 50 Servo Amplifier 52 Acousto-Optical Modulator (AOM) 54 Piezoelectric Actuator

Claims

1. A multi-laser base comb (MLC) light source, A narrow-linewidth laser-based optical pump that outputs pump light, A plurality of frequency laser combs coupled to the optical pump, each excited by the pump light received by the laser combs to generate output frequency combs in a range between a single octave and multiple octaves, wherein each laser comb is phase-locked to the optical pump and mutually coherent. An MLC light source equipped with [specific features / features].

2. The MLC light source according to claim 1, wherein the narrow-linewidth pump includes a single-frequency (SF) pump laser common to the plurality of laser combs, and operates in a continuous-wave (CW) or pulsed region such that pump light emitted from the SF pump laser is coupled to the combs.

3. The MLC light source according to claim 2, wherein the pump light propagating through each of the laser combs, when coupled to each of the laser combs, assists in generating a nonlinear effect (NLE), the NLE comprising three-wave mixing, self-phase modulation (SPM), and cross-phase modulation (XPM) in the PA of each laser comb, the output frequency comb output by each laser comb each comprises at least the respective fundamental (f) frequency, second harmonic (2f-SH), and superimposed comb of the broadband pump comb, the pump comb (p-comb) having the near-IR narrowband frequency component of the narrowband linewidth optical pump.

4. The MLC light source according to claim 3, wherein the output frequency comb further comprises at least one additional harmonic comb that is higher than the 2f-SH comb.

5. Each of the optical combs is configured using a master oscillator (MO) power amplifier (PA) architecture, the architecture including an MO that seeds the PA, the MO generating a series of ultrashort pulses of the f frequency that copropage with the pump light when coupled to the PA that generates the output frequency comb, according to claim 3.

6. The MLC light source according to claim 3, wherein each of the optical combs is configured using a laser that receives the pump light and generates the output frequency comb.

7. The MLC light source according to claim 5, wherein the MO and PA of each laser comb are selected from polycrystalline materials of the TM:II-VI group, and the polycrystalline materials used for each MO and PA of each laser comb are the same or different from each other.

8. The MLC light source according to claim 2, further comprising a plurality of pump amplifiers coupled between the SF laser and each laser comb, each receiving and amplifying the pump light that excites the laser comb.

9. The MLC light source according to claim 8, wherein each laser comb includes an MOPA configuration using an MO and a PA, and the MO and PA of each laser comb are excited by a single pump amplifier, or the MO and PA of each laser comb are excited by their respective pump amplifiers.

10. The MLC light source according to claim 8, wherein the common SF pump laser is selected from SF semiconductor, SF fiber laser or SF diode-pumped bulk laser and has a Fabry-Perot or ring resonator configuration, and the pump amplifier is solid or fiber amplifier.

11. The MLC light source according to claim 3, further comprising a plurality of beam guidance optics, each of which guides the output frequency comb of the laser comb along a path through a frequency discriminator, the frequency discriminator reflecting overlapping p-comb, f-frequency, and SH combs from the path and transmitting a portion of one of the fundamental frequency or SH comb.

12. The MLC light source according to claim 11, further comprising a plurality of notch filters, each of which separates the narrowband component of the narrow-linewidth pump from the rest of the pump comb, so that the output of the notch filters includes the filtered pump, f-frequency, and SH comb.

13. The MLC light source according to claim 12, further comprising a plurality of photodetectors (PDs), each of which detects the output from the notch filter and outputs an RF signal having a spectrum including an f0 signal and an fb signal, wherein the f0 signal corresponds to the carrier envelope offset (CEO) frequency of the laser comb and is the result of a beat between the f frequency and the SH comb, and the fb signal corresponds to the mutual phase relationship between the narrow linewidth pump and the laser comb and is a beat note that performs heterodyne processing of the f frequency, SH, and filtered p-comb.

14. The MLC light source according to claim 13, further comprising a plurality of phase-locked loops (LLPs), each pair of the plurality of LLPs receiving their respective f0 and fb signals from the PD, each pair of LLPs includes a respective phase-frequency detector (PFD) that receives their respective f0 and fb signals and compares them to a reference signal, and the PFD, upon determining a mismatch between each of the f0 and fb signals and the reference, outputs a respective control signal that is coupled to its respective servo amplifier.

15. The MLC light source according to claim 14, further comprising a plurality of acousto-optic modulators (AOMs) and comb laser resonant cavity actuators, each pair of the AOMs and the cavity actuators being operably connected to the laser comb and coupled to the respective servo amplifier outputs, so that the AOMs modulate the power of the narrow linewidth pump to adjust the CEO of the laser comb, and the resonant cavity actuators adjust the length of the resonant cavity of the laser comb to phase-lock the laser comb to the narrow linewidth pump.

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