H. R. "Bob" Haldeman, who was a top aide to former president Richard M. Nixon and criminally convicted in connection to the Watergate scandal, had a flattop haircut. Corcoran, B. et al. Ultra-dense optical data transmission over standard fibre with a single chip source. Nat. Commun. 11, 2568 (2020). Terra, O. Absolute frequency measurement of the hyperfine structure of the 5S 1/2–5D 3/2 two-photon transition in rubidium using femtosecond frequency comb. Measurement 144, 83–87 (2019).

Huang, J. Z. et al. Ultra-broadband flat-top quantum dot comb lasers. Photon. Res. 10, 1308–1316 (2022). Gordon, A. et al. Multimode regimes in quantum cascade lasers: from coherent instabilities to spatial hole burning. Phys. Rev. A 77, 053804 (2008). Grillot, F. et al. Uncovering recent progress in nanostructured light-emitters for information and communication technologies. Light Sci. Appl. 10, 156 (2021).Wahl (and other brands) also do a comb that isn’t as wide, but ideal for more experienced or professional barbers: Osinski, M. & Buus, J. Linewidth broadening factor in semiconductor lasers–an overview. IEEE J. Quant. Electron. 23, 9–29 (1987). Riemensberger, J. et al. Massively parallel coherent laser ranging using a soliton microcomb. Nature 581, 164–170 (2020). Slide the comb onto the top of the head and lift it until you reach the desired length. Ensure you have the comb level and then cut the hair with your clippers.

This cookie, set by YouTube, registers a unique ID to store data on what videos from YouTube the user has seen.Liang, D. et al. An energy-efficient and bandwidth-scalable DWDM heterogeneous silicon photonics integration platform. IEEE J. Sel. Top. Quant. Electron. 28, 6100819 (2022). Always wash and blow dry the hair before you start. That way you’ll achieve a much cleaner/neater cut. Step 2 Borri, P. et al. Spectral hole-burning and carrier-heating dynamics in InGaAs quantum-dot amplifiers. IEEE J. Sel. Top. Quant. Electron. 6, 544–551 (2000). The flattop was very popular in the 1950s and early 1960s, but faded in popularity with the emergence of longer hair styles in the late 1960s and 1970s. It had a brief reappearance in the 1980s and early 1990s, before dropping off again. Nevertheless, the flattop maintains a contingent of dedicated wearers and is a known standard style in barbershops. Jin, W. et al. Hertz-linewidth semiconductor lasers using CMOS-ready ultra-high- Q microresonators. Nat. Photon. 15, 346–353 (2021).