Spampinato, A; Stacey, C; Mulholland, S; Robertson, B; Klein, H A; Huang, G; Barwood, G P; Gill, P (2924) An ion trap design for a space-deployable strontium-ion optical clock. Proceedings of the Royal Society A, 480 (2284). 20230593

Trigatzis, M; Knapp, M; Mulholland, S; Hockley, G; Barwood, G P; Huang, G; Klein, H A; Gill, P (2024) Progress towards a transportable laser-cooled Yb+ microwave clock. In: 2024 European Frequency and Time Forum (EFTF), 25-27 June 2024, Neuchatel, Switzerland.

Mulholland, S; Donnellan, S; Barwood, G P; Gentle, D; Huang, Guilong; Klein, H A; Patel, P; Walsh, G; Baird, P.E.G.; Gill, P (2018) A Portable Microwave Clock Using Laser-Cooled Trapped 171Yb+Ions. In: 2018 IEEE International Frequency Control Symposium (IFCS), 21-24 May 2018, Olympic Valley, CA, USA.

Barwood, G P; Gill, P; Klein, H A; Hosaka, K; Huang, G; Lea, S N; Margolis, H S; Szymaniec, K; Walton, B R (2017) Trapped strontium ion optical clocks. Proceedings of the SPIE, 10567. 105672U

Barwood, G P; Huang, G; King, S A; Klein, H A; Gill, P (2016) Trapped-ion 88Sr+ optical clock systematic uncertainties - AC Stark shift determination. J. Phys.: Conf. Ser., 723. 012024

Dolezal, M*; Balling, P*; Nisbet-Jones, P B R; King, S A; Jones, J M; Klein, H A; Gill, P; Lindvall, T*; Wallin, A E*; Merimaa, M*; Tamm, C*; Sanner, C*; Huntemann, N*; Scharnhorst, N*; Leroux, I D*; Schmidt, P O*; Burgermeister, T*; Mehlstaubler, T E*; Peik, E* (2015) Analysis of thermal radiation in ion traps for optical frequency standards. Metrologia, 52 (6). pp. 842-856.

Barwood, G P; Huang, G; Klein, H A; Gill, P (2015) Automatic minimisation of micromotion in a 88Sr+ optical clock. Meas. Sci. Technol., 26 (7). 075203

Barwood, G P; Huang, G; King, S A; Klein, H A; Gill, P (2015) Frequency noise processes in a strontium ion optical clock. J. Phys. B, At. Mol. Opt. Phys., 48 (3). 035401

Barwood, G P; Huang, G; Klein, H A; Johnson, L A M; King, S A; Margolis, H S; Szymaniec, K; Gill, P (2014) Agreement between two 88Sr+ optical clocks to 4 parts in 10^17. Phys. Rev. A, 89 (5). 050501

Barwood, G P; Gill, P; Huang, G; Klein, H A (2012) Automatic laser control for a 88Sr+ optical frequency standard. Meas. Sci. Technol., 23 (5). 055201

Barwood, G P; Gill, P; Huang, G; Klein, H A (2012) Characterization of a 88Sr+ optical frequency standard at 445 THz by two-trap comparison. In: 2012 Conference on Precision Electromagnetic Measurements (CPEM 2012), 1-6 July 2012, Washington DC, USA.

Appourchaux, T*; Burston, R*; Chen, Y B*; Cruise, M*; Dittus, H*; Foulon, B*; Gill, P; Gizon, L*; Klein, H A; Klioner, S*; Kopeikin, S*; Kruger, H*; Lammerzahl, C*; Lobo, A*; Luo, X L*; Margolis, H S; Ni, W T*; Paton, A P*; Peng, Q H*; Peters, A*; Rasel, E*; Rudiger, A*; Samain, E*; Selig, H*; Shaul, D*; Sumner, T*; Theil, S*; Touboul, P*; Turyshev, S*; Wang, H T*; Wang, L*; Wen, L Q*; Wicht, A*; Wu, J*; Zhang, X M*; Zhao, C* (2009) Astrodynamical Space Test of Relativity Using Optical Devices I (ASTROD I)-A class-M fundamental physics mission proposal for Cosmic Vision 2015-2025. Exp. Astron., 23 (2). pp. 491-527.

Schiller, S*; Tino, G M*; Gill, P; Salomon, C*; Sterr, U*; Peik, E*; Nevsky, A*; Gorlitz, A*; Svehla, D*; Ferrari, G*; Poli, N*; Lusanna, L*; Klein, H A; Margolis, H S; Lemonde, P*; Laurent, P*; Santarelli, G*; Clairon, A*; Ertmer, W*; Rasel, E*; Muller, J*; Iorio, L*; Lommerzahl, C*; Dittus, H*; Gill, E*; Rothacher, M*; Flechner, F*; Schreiber, U*; Flambaum, V*; Ni, W T*; Liu, L*; Chen, X Z*; Chen, J B*; Gao, K L*; Cacciapuoti, L*; Holzwarth, R*; Hess, M P*; Schafer, W* (2009) Einstein Gravity Explorer-a medium-class fundamental physics mission. Exp. Astron., 22 (2). pp. 573-610.

Amelino-Camelia, G*; Aplin, K*; Arndt, M*; Barrow, J D*; Bingham, R J*; Borde, C*; Bouyer, P*; Caldwell, M*; Cruise, A M*; Damour, T*; D'Arrigo, P*; Dittus, H*; Ertmer, W*; Foulon, B*; Gill, P; Hammond, G D*; Hough, J*; Jentsch, C*; Johann, U*; Jetzer, P*; Klein, H A; Lambrecht, A*; Lamine, B*; Lammerzahl, C*; Lockerbie, N*; Loeffler, F*; Mendonca, J T*; Mester, J*; Ni, W T*; Pegrum, C*; Peters, A*; Rasel, E*; Reynaud, S*; Shaul, D*; Sumner, T J*; Theil, S*; Torrie, C*; Touboul, P*; Trenkel, C*; Vitale, S*; Vodel, W*; Wang, C*; Ward, H*; Woodgate, A* (2009) GAUGE: the GrAnd Unification and Gravity Explorer. Exp. Astron., 23 (2). pp. 549-572.

Ertmer, W*; Schubert, C*; Wendrich, T*; Gilowski, M*; Zaiser, M*; von Zoest, T*; Rasel, E*; Borde, C J*; Clairon, A*; Laurent, P*; Lemonde, P*; Santarelli, G*; Schleich, W*; Cataliotti, F S*; Inguscio, M*; Poli, N*; Sorrentino, F*; Modugno, C*; Tino, G M*; Gill, P; Klein, H A; Margolis, H S; Reynaud, S*; Salomon, C*; Lambrecht, A*; Peik, E*; Jentsch, C*; Johann, U*; Rathke, A*; Bouyer, P*; Cacciapuoti, L*; De Natale, P*; Christophe, B*; Foulon, B*; Touboul, P*; Maleki, L*; Yu, N*; Turyshev, S G*; Anderson, J D*; Schmidt-Kaler, F*; Walser, R*; Vigue, J*; Buchner, M*; Angonin, M C*; Delva, P*; Tourrenc, P*; Bingham, R*; Kent, B*; Wicht, A*; Wang, L J*; Bongs, K*; Dittus, H*; Lammerzahl, C*; Theil, S*; Sengstock, K*; Peters, A*; Muller, T*; Arndt, M*; Iess, L*; Bondu, F*; Brillet, A*; Samain, E*; Chiofalo, M L*; Levi, F*; Calonico, D* (2009) Matter wave explorer of gravity (MWXG). Exp. Astron., 23 (2). pp. 611-649.

Wolf, P*; Borde, C J*; Clairon, A*; Duchayne, L*; Landragin, A*; Lemonde, P*; Santarelli, G*; Ertmer, W*; Rasel, E*; Cataliotti, F S*; Inguscio, M*; Tino, G M*; Gill, P; Klein, H A; Reynaud, S*; Salomon, C*; Peik, E*; Bertolami, O*; Gil, P*; Paramos, J*; Jentsch, C*; Johann, U*; Rathke, A*; Bouyer, P*; Cacciapuoti, L*; Izzo, D*; De Natale, P*; Christophe, B*; Touboul, P*; Turyshev, S G*; Anderson, J*; Tobar, M E*; Schmidt-Kaler, F*; Vigue, J*; Madej, A A*; Marmet, L*; Angonin, M C*; Delva, P*; Tourrenc, P*; Metris, G*; Muller, H*; Walsworth, R*; Lu, Z H*; Wang, L J*; Bongs, K*; Toncelli, A*; Tonelli, M*; Dittus, H*; Lammerzahl, C*; Galzerano, G*; Laporta, P*; Laskar, J*; Fienga, A*; Roques, F*; Sengstock, K* (2009) Quantum physics exploring gravity in the outer solar system: the SAGAS project. Exp. Astron., 23 (2). pp. 651-687.

Hein, G*; Moudrak, A*; Klein, H A; Eissfeller, B* (2008) Opportunities for using optical clocks in GNSS systems. Inside GNSS (Sept/O). pp. 45-50.

Flowers, J L; Baird, P E G*; Evans, A*; Klein, H A; Langham, C D; Mairiniac, L*; Margolis, H S; Walton, B R (2008) Optical spectroscopy of atomic hydrogen for an improved determination of the Rydberg constant. In: Proceedings of the 7th Symposium on Frequency Standards and Metrology., 5-11 October 2008, Pacific Grove, California, USA.

Margolis, H S; Barwood, G P; Huang, G; Klein, H A; Lea, S N; Marra, G; Tsatourian, V; Walton, B R; Gill, P (2008) An optical clock based on a single trapped 88Sr+ ion. In: Proceedings of the 7th Symposium on Frequency Standards and Metrology., 5-11 October 2008, Pacific Grove, California, USA.

Flowers, J L; Baird, P E G*; Bougueroua, L; Klein, H A; Margolis, H S (2007) The NPL Rydberg constant experiment. IEEE Trans. Instrum. Meas., 56 (2). pp. 331-335.

Barwood, G P; Gill, P; Huang, G; Klein, H A (2007) Observation of a sub-10-Hz linewidth 88Sr+ 2S1/2-2D5/2 clock transition at 674 nm. IEEE Trans. Instrum. Meas., 56 (2). pp. 226-229.

Flowers, J L; Baird, P E G*; Bougueroua, L; Klein, H A; Margolis, H S (2006) The NPL Rydberg constant experiment. In: CPEM 2006 Conference on Precision Electromagnetic Measurements, 9-14 July 2006, Torino, Italy.

Barwood, G P; Gill, P; Klein, H A; Huang, G; Walton, B R (2006) An optical frequency standard based on a transition in a single trapped strontium ion. In: CPEM 2006 Conference on Precision Electromagnetic Measurements, 9-14 July 2006, Torino, Italy.

Barwood, G P; Gill, P; Klein, H A; Huang, G; Walton, B R (2006) An optical frequency standard based on a transition in a single trapped strontium ion. In: CPEM 2006 Conference on Precision Electromagnetic Measurements, 9-14 July 2006, Torino, Italy.

Barwood, G P; Huang, G; Klein, H A; Margolis, H S; Lea, S N; Szymaniec, K; Chalupczak, W; Gill, P (2006) An optical frequency standard based on a transition in a single trapped strontium ion. In: Optical Frequency Combs for Space International Workshop, 2-3 October 2006, NPL, UK.

Margolis, H S; Huang, G; Lea, S N; Barwood, G P; Klein, H A; Gill, P (2004) Comparison of two femtosecond optical frequency combs at NPL. In: Conference on Precision Electromagnetic Measurements (CPEM) 2004, 27 June - 2 July 2004, London, UK.

Barwood, G P; Margolis, H S; Huang, G; Gill, P; Klein, H A (2004) Determination of the quadrupole frequency shift of the 2S1/2 2D5/2 transition in 88Sr+ at 674 nm. In: Conference on Precision Electromagnetic Measurements (CPEM) 2004, 27 June - 2 July 2007, London, UK.

Margolis, H S; Barwood, G P; Huang, G; Klein, H A; Lea, S N; Szymaniec, K; Gill, P (2004) Hertz-level measurement of the optical clock frequency in a single 88Sr+ ion. Science, 306 (5700). pp. 1355-1358.

Flowers, J L; Klein, H A; Margolis, H S; Reed, R P (2004) Precision spectroscopy of metastable atomic hydrogen: towards an improved determination of the Rydburg constant. In: Conference on Precision Electromagnetic Measurements (CPEM) 2004, 27 June - 2 July 2004, London, UK.

Margolis, H S; Huang, G; Barwood, G P; Lea, S N; Klein, H A; Rowley, W R C; Gill, P; Windeler, R S* (2003) Absolute frequency measurement of the 674 nm 88Sr+ clock transition using a femtosecond optical frequency comb. Phys. Rev. A, At. Mol. Opt. Phys., 67. 032501

Barwood, G P; Gao, K*; Gill, P; Huang, G; Klein, H A (2003) Observation of the hyperfine structure of the 2S1/2 - 2D5/2 674 nm optical clock transition in 87Sr+. Phys. Rev. A, At. Mol. Opt. Phys., 67. 013402

Margolis, H S; Barwood, G P; Blythe, P J; Gill, P; Hosaka, K; Huang, G; Klein, H A; Lea, S N; Webster, S A (2003) Trapped ion optical Frequency standards and metrology. In: Digest of LEOS Summer Topical Meeting on Photonic Time/Frequency Measurement and Control, 14-16 July 2003, Vancouver, Canada.

Gill, P; Barwood, G P; Klein, H A; Huang, G; Webster, S A; Blythe, P J; Hosaka, K; Lea, S N; Margolis, H S (2003) Trapped ion optical frequency standards. Meas. Sci. Technol., 14 (8). pp. 1174-1186.

Klein, H A; Knight, D J E*; Plimmer, M D*; Silver, J D* (2002) DTI scouting mission to Japan on Trapped Ions for Measurement and Enterprise (TIME) 26th - 30th November 2001. NPL Report. CBTLM 17

Lea, S N; Margolis, H S; Huang, G; Barwood, G P; Klein, H A; Blythe, P J; Webster, S A; Rowley, W R C; Gill, P; Windeler, R S* (2002) Femtosecond comb measurements of optical frequency standards at NPL. In: IEEE-LEOS 2002 15th Annual Meeting of the IEEE Lasers and Electo-Optics Society., 10-14 November 2002, Glasgow, UK.

Lea, S N; Margolis, H S; Huang, G; Rowley, W R C; Henderson, D; Barwood, G P; Klein, H A; Webster, S A; Blythe, P; Gill, P (2002) Femtosecond optical frequency comb measurements of lasers stabilised to transitions in 88Sr+, 171Yb+ and I2 at NPL. In: Proceedings of the 6th Symposium on Frequency Standards and Metrology, 9-14 September 2001, University of St Andrews, Fife, Scotland, UK.

Barwood, G P; Gill, P; Huang, G; Klein, H A (2002) Stability and reproducibility of an optical frequency standard based upon the 2S1/2 - 2D5/2 transition in 88Sr+. In: Proceedings of the 6th Symposium on Frequency Standards and Metrology, 9-14 September 2001, University of St Andrews, Fife, Scotland, UK.

Flowers, J L; Klein, H A; Knight, D J E; Margolis, H S (2001) Hydrogenic systems for calculable frequency standards: status and options. NPL Report. CBTLM 11

Barwood, G P; Gao, K; Gill, P; Huang, G; Klein, H A (2001) Development of an ultra-narrow diode laser for interrogating the 674 nm 2S1/2 - 2D5/2 'clock' transition in Sr+. Proc. SPIE - Int. Soc. Opt. Eng., 4269. pp. 134-142.

Barwood, G P; Gao, K*; Gill, P; Huang, G; Klein, H A (2001) Development of optical frequency standards based upon the 2S1/2-2D5/2 transition in 88Sr+ and 87Sr+. IEEE Trans. Instrum. Meas., 50 (2). pp. 543-547.

Barwood, G P; Gao, K; Gill, P; Huang, G; Klein, H A (2000) Development of optical frequency standards based upon the 2S1/2 - 2D5/2 transition in 88Sr+. In: Conference on Precision Electromagnetic Measurements (CPEM) 2000, 14-19 May 2000, Sydney, Australia.

Klein, H A; Barwood, G P; Gill, P; Huang, G (2000) Single trapped ions for optical frequency standards. Phys. Scr. Vol. T, 86. pp. 33-37.

Klein, H A; Knight, D J E (1999) A study of ultra-stable optical clocks, frequency sources and standards for space applications. NPL Report. CBTLM 2

Barwood, G P; Gill, P; Huang, G; Klein, H A (1999) Development of an optical frequency standard based upon the 2S1/2-2D5/2 transition in Sr+. In: 13th EFTF/ 1999 IEEE FCS Conference Proceedings, 1999.

Barwood, G P; Huang, G; Klein, H A; Gill, P; Clarke, R B M* (1999) Sub-kHz comparison of the single-ion optical-clock 2S1/2 - 2D5/2 transition in two 88Sr+ traps. Phys. Rev. A, At. Mol. Opt. Phys., 59. R3178-81

Barwood, G P; Gill, P; Klein, H A; Rowley, W R C (1998) Sub-kHz "clock" transition linewidths in a cold trapped 88Sr+ ion in low magnetic fields using 1092-nm polarisation switching. Opt. Commun., 151 (1-3). pp. 50-5.

Clarke, R B W*; Riis, E*; Barwood, G P; Gill, P; Huang, G; Klein, H A (1998) A sideband-injection locked extended cavity diode laser for interrogating cold trapped strontium ions. Opt. Commun., 158 (1-6). pp. 36-40.

Barwood, G P; Gill, P; Klein, H A; Rowley, W R C (1997) Clearly resolved secular sidebands on the 2S1/2-2D5/2 674nm clock transition in a single trapped Sr+ ion and prospects for trapped ion frequency standards. IEEE Trans. Instrum. Meas., 46 (2). pp. 133-136.

Roberts, M; Taylor, P; Barwood, G P; Gill, P; Klein, H A; Rowley, W R C (1997) Observation of an electric octupole transition in a single Ion. Phys. Rev. Lett., 78 (10). pp. 1876-1879.

Barwood, G P; Gill, P; Huang, G; Klein, H A; Rowley, W R C (1997) Single Sr+ Ion spectroscopy with a sub-kHz linewidth diode probe laser. In: 13th International Conference on Laser Spectroscopy, June 1997, Hangzhou, China.

Gill, P; Klein, H A; Roberts, M; Rowley, W R C; Taylor, P (1996) Absolute measurement of the 2S1/2 - 2D5/2 411nm interval, and the search for the 2S1/2 - 2F7/2 467nm transition in laser-cooled trapped 172Yb+. In: Proc. Fifth symposium on Frequency Standards and Metrology, 1996, Singapore.

Barwood, G P; Gill, P; Klein, H A; Rowley, W R C (1996) Observation of fluorescence from cold trapped Sr ions in a near-zero magnetic field and 674nm probe laser development. In: Proc. Fifth symposium of Frequency Standards and Metrology, 1996, Singapore.

Gill, P; Klein, H A; Levick, A P; Rowley, W R C; Taylor, P (1995) Measurement of the 2S1/2 - 2D5/2 411 nm interval in laser-cooled 172Yb+ ions. Phys. Rev. A, At. Mol. Opt. Phys., 52. R909-912

Barwood, G P; Edwards, C S; Gill, P; Huang, G; Klein, H A; Rowley, W R C (1995) Precision interferometric frequency measurement of the 674nm 2S1/2 - 2D5/2 transition in a single cold Sr+ ion. IEEE Trans. Instrum. Meas., 44 (2). pp. 117-119.

Barwood, G P; Gill, P; Huang, G; Klein, H A (1995) Studies of trapped strontium ions in low magnetic fields. Appl. Phys. B, Laser Opt., 61 (4). p. 385.

Barwood, G P; Edwards, C S; Gill, P; Klein, H A; Rowley, W R C (1994) Laser cooling and probing of a trapped strontium ion using all-solid-state lasers. AIP Conf. Proc., 290. pp. 35-37.

Edwards, C S; Gill, P; Klein, H A; Levick, A P; Rowley, W R C (1994) Laser-cooling effects in few-ion clouds of Yb/sup +/. Appl. Phys. B, Laser and Optics, B59 (2). 179 - 185

Edwards, C S; Gill, P; Klein, H A; Levick, A P; Rowley, W R C (1994) Precision measurement of the 2S1/2(2 sps-1/2 sbs) - 2D5/2(2 sps-5/2 sbs) 411 nm transition in laser-cooled 172Yb+ (172 & + in sps) ions. In: 5th European Quantum Electronics Conference, Technical Digest, 53, 1994, Amsterdam, Holland.

Gill, P; Klein, H A; Levick, A P; Roberts, M; Rowley, W R C; Taylor, P (1994) A search for the 2S1/2 (2 sps - 1/2sbs) - 2F7/2 (2 sps -7/2sbs) 467 nm transition in laser cooled 172Yb+. (172 & + sps). In: 14th International Conference Digest on Atomic Physics, 1994, Boulder, Colorado, USA.

Barwood, G P; Edwards, C S; Gill, P; Klein, H A; Rowley, W R C (1993) Development of diode and fibre laser sources for a Sr+ trapped ion optical frequency standard. Proc. SPIE - Int. Soc. Opt. Eng., 1837. pp. 271-7.

Barwood, G P; Edwards, C S; Gill, P; Klein, H A; Rowley, W R C (1993) Observation of the 5s2S1/2-4d2D5/2 transition in a single laser-cooled trapped Sr+ ion using an all-solid-state system of lasers. Opt. Lett., 18 (9). pp. 732-734.