Winter sunlight filtered through the clean observation window, spreading across the epoxy‑resin floor of the lithography‑machine R&D base laboratory, casting cold, bright light‑spots. Air filled with constant equipment hum and slight airflow sounds from the circulating‑filtration system—everything seemed returned to orderly scientific rhythm. Xiuxiu stood beside the EUV lithography‑machine engineering prototype—which had undergone the first successful tape‑out yet now faced new challenges in even more advanced domains—brows slightly furrowed, gaze sharply scanning a set of freshly‑released test‑data reports. The problem still focused on that long‑plaguing core difficulty: EUV light‑source collection efficiency.
The extreme‑ultraviolet plasma generated by laser bombardment of tin droplets resembled a brief, violent miniature sun, radiating precious 13.5‑nanometer‑wavelength photons in all directions. Yet their existing collector‑mirror system, despite employing most‑advanced multilayer‑Bragg‑reflector technology, still had theoretical and technical upper limits regarding solid‑angle collection efficiency. Vast numbers of invaluable photons, like spilled mercury, failed being effectively captured and directed toward silicon wafers, instead wasted dissipating within vacuum chamber. This directly limited lithography‑machine throughput, becoming a critical bottleneck on the road toward higher production capacity. The team had tried multiple optimization schemes—from adjusting collector‑mirror curved‑surface shapes to optimizing multilayer‑film reflectivity curves—some gains existed, yet never achieved qualitative breakthrough. A familiar sense of stiffness when facing hard technological barriers again enveloped the laboratory atmosphere.
Xiuxiu felt a trace irritation; she walked to the control console, subconsciously pulling up earlier in‑depth exchange records with Yue'er. That wasn't merely about mask‑defect mathematical modeling, but also some early, more‑conceptual‑discussion dialogues. She needed shift mind‑set, needed temporarily disengage from that engineering thinking drilling into dead‑ends. Her gaze unconsciously browsed those conversation fragments filled with abstract terminology—until a description about "mathematical structures" and "intrinsic vibrational modes," like a faint electric arc, abruptly crossed her mind.
That was Yue'er describing a conception when attempting unifying different L‑functions. She had metaphorized: different mathematical objects might resemble "harmonic oscillators" possessing different natural frequencies; seeking duality or unification among them perhaps resembled finding a coupling mechanism enabling these different oscillators to undergo "resonance," thereby exciting more powerful, synergistic "vibrations." Yue'er then emphasized "resonance" possibilities among mathematical structures themselves.
"Resonance… frequency… coupling…" Xiuxiu murmured to herself; engineer's instinct instantly connected these abstract mathematical metaphors with the physical reality she currently tackled. Plasma! Laser‑generated tin plasma—it itself wasn't a stable light‑source; its emission behavior, perhaps also possessed certain intrinsic, resonatable modes? If such modes could be found and excited, could that make plasma radiate EUV photons more concentratedly, more efficiently in specific, collection‑favorable directions?
This idea made her whole‑body tremble—as if seeing a thread of completely‑new light at dark tunnel's end. She immediately set aside earlier test reports, rushed to computer, called up physical‑simulation software regarding laser‑generated plasma and massive related research literature. She needed verify this inspiration's feasibility.
Traditional EUV light‑source collector‑mirror designs relatively "passive." It resembled a maximally‑opened, extremely‑high‑reflectivity "dustpan," waiting to catch randomly‑splashing photons from all directions. Its efficiency improvements primarily relied on geometric‑shape optimization and reflection‑film‑layer performance‑limit excavation.
Whereas the "resonance" approach introduced an "active" excitation possibility. Xiuxiu's brain rapidly operated, combining plasma‑physics knowledge, beginning outlining a new theoretical framework:
**Plasma Resonance and Collective Behavior:** When high‑power laser‑focus bombardment strikes tin droplets, the formed plasma wasn't a uniform mass—its interior contained density, temperature‑varying regions, plus free‑electron and ion collective oscillations. These collective oscillations—**plasma oscillations**—possessed their inherent frequency (plasma frequency), correlating with electron density. More importantly, within specific non‑uniform plasma structures (e.g., laser‑pre‑pulse‑formed disc‑like tin targets), certain specific, spatially‑localized **resonance modes** might be excited—e.g., similar to surface‑plasmon‑enhancement effects, or specific electromagnetic modes related to plasma‑cavity morphology. Under these resonance modes, plasma absorption of laser energy and conversion toward EUV‑light efficiency might be enormously enhanced in specific frequencies and spatial directions!
This resembled striking a tuning‑fork—it would strongly vibrate and emit sound at its inherent frequency. If could use "laser‑hammer" correctly "strike" tin‑droplet plasma, exciting its intrinsic "resonant‑tuning‑fork" mode, then its EUV‑light‑radiation "sound" (intensity and behavior) would undergo qualitative change!
**Synergistic Design of Optical Collector‑Mirror:** If plasma truly possessed such excit‑able, direction‑enhance‑able radiation modes, then collector‑mirror design philosophy required fundamental transformation! It should evolve from a passive "collection‑dustpan" into part of a **strong‑coupled resonance‑cavity** with the plasma resonance source!
Xiuxiu began constructing new models within design software. She envisioned substantially modifying collector‑mirror shape—no longer merely pursuing maximum solid collection angle, but instead constructing its inner surface into a specific structure resembling **rotational‑ellipsoid‑surface or composite‑freeform‑surface**. This new structure's core design target was matching its optical characteristics (focal point, aberrations) precisely with anticipated plasma‑resonance‑mode spatial‑radiation characteristics.
Her thought‑path increasingly clear; fingers flew across keyboard, recording core points:
**Resonance Excitation and Control:** Required fine‑tuning control over laser‑pulse morphology (especially pre‑pulse and main‑pulse intensity, delay, spatial profile)—no longer merely flattening tin droplets, but deeper purpose: **preparing plasma structures supporting specific electromagnetic‑resonance modes** consciously during initial stages of tin‑droplet transformation into plasma. This demanded deeper understanding and more‑precise control over laser‑matter‑interaction physics. **Collector‑Mirror‑Resonance‑Cavity Integration:** New‑type collector‑mirror design required **collaborative simulation optimization** with anticipated plasma resonance source. Goal: letting collector‑mirror inner surface precisely converge resonance‑enhanced‑radiation‑emitted EUV‑light wavefronts, with minimal aberration and energy loss, onto intermediate‑focus (IF). This equivalently constructed an **unstable‑resonance‑cavity** using plasma resonance region as primary light‑source, specific‑shaped collector‑mirror as reflection‑wall—using cavity geometry to filter and enhance specific radiation modes. **Multi‑Physics‑Field Coupling Simulation:** This was an extremely complex multi‑physics problem—involving laser physics, plasma dynamics, radiation transport, computational electromagnetics (solving Maxwell equations), plus thermo‑mechanical coupling (collector‑mirror thermal deformation affecting optical performance). Traditional design‑flow must be broken; needed introducing more‑powerful coupling‑simulation tools and algorithms.
This conception elevated EUV light‑source generation and collection from a relatively‑separated "source‑mirror" system into a highly‑integrated "**source‑mirror‑resonance‑coupling**" system! Potential gains enormous—if successful, not only might significantly enhance collection efficiency (possibly breaking existing theory's 5% or even 10% bottlenecks), but also improve light‑source bandwidth and stability—because resonance modes often exhibit better characteristics and anti‑interference capability.
Certainly, challenges equally unprecedented. This required deeper exploration into plasma physics; laser‑parameter control demands reaching unprecedented precision; collector‑mirror manufacturing and inspection raising near‑inhuman requirements (surface‑shape precision needing adapt resonance‑modes, not simple geometric imaging); and entire design‑verification cycle extremely long and expensive.
But Xiuxiu's eyes already ignited long‑absent, conquest‑filled flames. This was innovation originating from most‑fundamental physical principles; disruptive thinking jumping beyond original technological frameworks. She immediately convened core members of the light‑source team; before whiteboard, she passionately expounded this new theoretical conception based on "resonant‑state revelation."
Initially, team members' faces filled astonishment, disbelief. This completely overturned design paradigms they'd been accustomed to for years. Yet as Xiuxiu layered in‑depth analysis—from plasma‑resonance physics to optical‑resonance‑cavity synergistic design, then potential enormous performance gains—questioning gradually replaced by intense discussion and eager‑to‑try excitement. This was a high‑risk, high‑reward direction, yet undoubtedly pointing toward a tempting path ascending higher peaks.
Meeting lasted several hours; ultimately team reached consensus—immediately establish "resonance‑coupled‑light‑source" pre‑research group, led personally by Xiuxiu, drawing elite members, initiating preliminary theoretical research and feasibility verification.
When commotion dispersed, Xiuxiu remained alone in laboratory, gazing at those scribbled yet vitality‑filled formulas and sketches on whiteboard—heart brimming surging passion and deep gratitude. This breakthrough inspiration didn't originate from her familiar engineering domain, but from Yue'er's seemingly‑unrelated mathematical world—a chance "resonance."
She picked up encrypted communicator, without hesitation, simultaneously dialed Mozi and Yue'er within small group.
Video connection established; Mozi's figure appeared on screen—background seemingly his trading room; Yue'er's image from her Shanghai temporary residence—face complexion rosier than before.
"Xiuxiu? Something urgent?" Mozi asked; Yue'er also cast inquiring gaze.
"I have an important idea, want inform you both first‑moment." Xiuxiu's voice slightly trembled due excitement; she pulled whiteboard before camera, began briefly, using simplest‑possible language, expounding her new conception about "plasma resonance" and "collector‑mirror‑resonance‑cavity integration."
"…The origin of this idea is Sister Yue'er." Xiuxiu's gaze turned Yue'er, eyes clear sincere. "Your earlier metaphor about mathematical‑structure 'resonance'—like a key, suddenly opened a door within my thinking never before opened. Sister Yue'er, thank you! Without your inspiration, I might still circling original dead‑end."
Yue'er on‑screen clearly stunned. She watched Xiuxiu's whiteboard complex physical formulas and optical schematic diagrams, listening her passion‑filled description—though many engineering details not fully understood—could clearly feel: her own abstract, mathematical‑world "resonance" reverie actually bore such concrete, disruptive technological fruit here! A marvelous, cross‑disciplinary‑barrier creation thrill made her pale cheeks flush with excitement‑tinged rosiness.
"Xiuxiu… I… merely spoke casually…" Yue'er somewhat embarrassed, yet eyes filled happiness for Xiuxiu's success, "Able inspire your research even slightly—I truly feel joy! This idea sounds… extremely profound!"
Mozi quietly listened; watching screen's two equally‑exceptional yet shining different‑dimension women—because once intellectual collision sparking such dazzling brilliance—heart filled ineffableemotion and deep satisfaction. He saw Xiuxiu's un‑contrived gratitude toward Yue'er; saw Yue'er's genuine delight for Xiuxiu's success. Between them—no jealousy or estrangement because of him; instead precisely this intellectual mutual‑nourishment and career mutual‑support establishing solid, healthy bond.
He smiled, gaze gentle sweeping both screens, said: "Seems our 'resonance'—not merely emotionally, but deeper within creativity's core. Xiuxiu, this is remarkable direction, deserves full investment. Yue'er, your mathematical cosmos again demonstrates its power transcending boundaries."
His words like gentle wind brushing three hearts. Xiuxiu's breakthrough attributed Yue'er's inspiration; Yue'er's value proven through Xiuxiu's success; Mozi—connecting, witnessing, supporting all this occurrence. A dynamic, vitality‑filled equilibrium, within this highest‑level‑appreciation‑support‑based interaction, quietly consolidated. Competition? Perhaps existed—but that was a benign competition urging each other climb higher. Collaboration? Already deep‑embedded marrow, crossing discipline gulfs and emotional subtlety. These three, seemingly formed a stable triangle—each side because other two sides' existence becoming more resilient; jointly supporting a future vision far exceeding individual dreams.
Xiuxiu looked at screen's Mozi and Yue'er—heart clear‑illumined. Future road still challenge‑filled; but this new direction originating "resonant‑state revelation" made her brimming infinite fighting spirit. Having two fellow‑travelers shining like stars mutually‑illuminating—this perhaps her life's greatest fortune. Laboratory lights cold, but her heart's flames already burned extremely intense for upcoming, more‑arduous struggles.