- Email: [email protected]
The stanford picosecond FEL center
-_ .-__ IIB
2s
Nuclear Instruments
and Methods
in Physics Research
A 375 (1996) 662-663
NUCLEAR INSTRUMENTS A METHODS IN PHYSICS RESEARCH Section A
ELSEYIER
The Stanford Picosecond H.A. Schwettman”, Stanford Picosecond
FEL Center, W.W. Hansen Experimental
T.I. Smith, R.L. Swent Physics Laboratory,
In the past year there have been significant increases in quantity and quality of FEL beam available at the Stanford picosecond FEL center. The new mid-IR FEL has been brought into full operation from 3 to 12 km and has produced substantially higher peak and average power than was available in the past. The far-IR FEL has operated from 15 to 65 p,rn and will soon be ready for user operation. The number of hours of experimenter’s beam time has increased to over 2000 hours per year, and the the
Table 1 Operating
parameters
for the lasers Mid-IR
Wavelength Micropulse width Micropulse repetition rate Macropulse width Macropulse repetition rate Micropulse energy Average power Spectra1 bandwidth Spectral stability Amplitude stability
Table 2 Summary
of operating
(STI)
Far-IR (FIREFLY)
3-12 pm 0.7-3 ps 84.6 ns 5 ms 20 Hz
15-65 pm 2-10 ps 84.6 ns 5ms 20 Hz
1 FJ
1 PJ
1.2w Transform-limited Gaussian 0.01% rms <2% rms
1.2 w Transform-limited Gaussian 0.01% rms <2% rms
FEL Center Stanford University, Stanford, CA 94305-408-7, USA
macropulse repetition rate has routinely been 20 Hz instead of the 10 Hz of previous years, allowing more data collection in each hour of beam time. Table I lists the current operating parameters for the mid-IR and far-IR lasers. Table 2 shows how the operating time was divided among the different classes of experiments. Several of the experimental areas have undergone extensive modifications. New purge enclosures have been built to improve operation at wavelengths with strong atmospheric absorption. An additional experimental station has been added in room FEL 1 to allow concurrent users to operate continuously with a small fraction of the beam. On occasion the beam has been split again downstream, allowing three experiments to run simultaneously. A single-color mid-infrared facility has been established in FEL 2. In this room a pulse selector and alignment system precedes 3 dedicated stations: I ) a pump-probe and photon echo station, 2) a station for transient grating and stimulated echo experiments and 3) a single-beam station. FEL rooms 3 and 4 have been combined and hold the synchronized Ti : sapphire laser with its newly-added amplifier. The amplified pulses are 150 p,J at a 5 kHz rate for use in two-color experiments. A new room has also been built for experiments which use the far-IR FEL. A wide variety of pump-probe experiments have been performed. Measurements of the vibrational relaxation of
time for the year Ott-Nov ‘94
Feb-Apr ‘95
July-Aug ‘95”
Start-up and maintenance time [h] FEL experimental time [h]
125
329
251
System development FEL & accelerator science Solid state and surface science Molecular materials and chemistry Biophysics and medical science Total experimental time [h]
99 82 + 24b 99 119 122 521 + 24b
121 253 + 19b 160 134 214 + gb 882 + 27b
124+41b 31 65 82 143 + 164” 445 + 205 b
a Run in progress at time of writing. ’ Parasitic FEL experimental time. * Corresponding
Final totals may differ slightly
author.
0168-9002/96/$15.00 Copyright PII SO168-9002(96)00051-4
0 1996 Elsevier Science B.V. All rights reserved
Fiscal year Total 705 385 409 324 335 651 2104
H.A. Schwettman
et al. I Nucl. Instr. and Meth. in Phvs. Res. A 375 (1996) 662-663
SH, SD and D,O in A@, have led to the conclusion that the relaxation of small molecules is much more complex than that predicted by the so-called “gap-law”. The temperature dependent vibrational relaxation of the CO stretching mode of rhodium dicarbonyl acetylacetonate (Rh(CO),(acac)) and tungsten hexacarbonyl (W(CO),) in dibutylphthalate (DBP) and 2-methylpentane (2-MP) were measured from 10 to 300 K. Both the parallel and magic angle probe polarizations decay curves are bi-exponential over the entire temperature range. For the fast component, a mechanism of spectral diffusion has been proposed, in contrast to the previously proposed mechanism of scattering between closely spaced vibrational levels. The vibrational relaxation of CO bound to a series of metalloporphyrin complexes was measured. The dependence of relaxation rate on the mass of the metal ion rules out coupling through a sigma bond and is interpreted as arising from a pi-bond coupling between the CO vibrational fundamental and the porphyrin vibrations. The vibrational lifetime of the protein amide I band has
663
been measured using single-color infrared transient absorption spectroscopy. The vibrational excitation relaxes rapidly: within 3 ps. The dependence of lifetime on protein structure and on temperature has been measured for three native proteins; myoglobin, azurin and cytochrome c. The tunability of the FBL in combination with its high brightness makes it a nearly ideal source for scanning near-field infrared spectroscopy applications. High resolution infrared images have been obtained on renal tissue sections, using the intrinsic contrast provided by the vibrational absorption bands from identified molecular species within the tissue. The instrument is expected to be used for novel microspectroscopic applications not only in biophysical studies, but also in materials science.
Acknowledgement This work has been supported in part by the Office of Naval Research, Grant No. NOOOl4-94-l-1024.
IX. FEL FACILITY CHALLENGES
2s
Nuclear Instruments
and Methods
in Physics Research
A 375 (1996) 662-663
NUCLEAR INSTRUMENTS A METHODS IN PHYSICS RESEARCH Section A
ELSEYIER
The Stanford Picosecond H.A. Schwettman”, Stanford Picosecond
FEL Center, W.W. Hansen Experimental
T.I. Smith, R.L. Swent Physics Laboratory,
In the past year there have been significant increases in quantity and quality of FEL beam available at the Stanford picosecond FEL center. The new mid-IR FEL has been brought into full operation from 3 to 12 km and has produced substantially higher peak and average power than was available in the past. The far-IR FEL has operated from 15 to 65 p,rn and will soon be ready for user operation. The number of hours of experimenter’s beam time has increased to over 2000 hours per year, and the the
Table 1 Operating
parameters
for the lasers Mid-IR
Wavelength Micropulse width Micropulse repetition rate Macropulse width Macropulse repetition rate Micropulse energy Average power Spectra1 bandwidth Spectral stability Amplitude stability
Table 2 Summary
of operating
(STI)
Far-IR (FIREFLY)
3-12 pm 0.7-3 ps 84.6 ns 5 ms 20 Hz
15-65 pm 2-10 ps 84.6 ns 5ms 20 Hz
1 FJ
1 PJ
1.2w Transform-limited Gaussian 0.01% rms <2% rms
1.2 w Transform-limited Gaussian 0.01% rms <2% rms
FEL Center Stanford University, Stanford, CA 94305-408-7, USA
macropulse repetition rate has routinely been 20 Hz instead of the 10 Hz of previous years, allowing more data collection in each hour of beam time. Table I lists the current operating parameters for the mid-IR and far-IR lasers. Table 2 shows how the operating time was divided among the different classes of experiments. Several of the experimental areas have undergone extensive modifications. New purge enclosures have been built to improve operation at wavelengths with strong atmospheric absorption. An additional experimental station has been added in room FEL 1 to allow concurrent users to operate continuously with a small fraction of the beam. On occasion the beam has been split again downstream, allowing three experiments to run simultaneously. A single-color mid-infrared facility has been established in FEL 2. In this room a pulse selector and alignment system precedes 3 dedicated stations: I ) a pump-probe and photon echo station, 2) a station for transient grating and stimulated echo experiments and 3) a single-beam station. FEL rooms 3 and 4 have been combined and hold the synchronized Ti : sapphire laser with its newly-added amplifier. The amplified pulses are 150 p,J at a 5 kHz rate for use in two-color experiments. A new room has also been built for experiments which use the far-IR FEL. A wide variety of pump-probe experiments have been performed. Measurements of the vibrational relaxation of
time for the year Ott-Nov ‘94
Feb-Apr ‘95
July-Aug ‘95”
Start-up and maintenance time [h] FEL experimental time [h]
125
329
251
System development FEL & accelerator science Solid state and surface science Molecular materials and chemistry Biophysics and medical science Total experimental time [h]
99 82 + 24b 99 119 122 521 + 24b
121 253 + 19b 160 134 214 + gb 882 + 27b
124+41b 31 65 82 143 + 164” 445 + 205 b
a Run in progress at time of writing. ’ Parasitic FEL experimental time. * Corresponding
Final totals may differ slightly
author.
0168-9002/96/$15.00 Copyright PII SO168-9002(96)00051-4
0 1996 Elsevier Science B.V. All rights reserved
Fiscal year Total 705 385 409 324 335 651 2104
H.A. Schwettman
et al. I Nucl. Instr. and Meth. in Phvs. Res. A 375 (1996) 662-663
SH, SD and D,O in A@, have led to the conclusion that the relaxation of small molecules is much more complex than that predicted by the so-called “gap-law”. The temperature dependent vibrational relaxation of the CO stretching mode of rhodium dicarbonyl acetylacetonate (Rh(CO),(acac)) and tungsten hexacarbonyl (W(CO),) in dibutylphthalate (DBP) and 2-methylpentane (2-MP) were measured from 10 to 300 K. Both the parallel and magic angle probe polarizations decay curves are bi-exponential over the entire temperature range. For the fast component, a mechanism of spectral diffusion has been proposed, in contrast to the previously proposed mechanism of scattering between closely spaced vibrational levels. The vibrational relaxation of CO bound to a series of metalloporphyrin complexes was measured. The dependence of relaxation rate on the mass of the metal ion rules out coupling through a sigma bond and is interpreted as arising from a pi-bond coupling between the CO vibrational fundamental and the porphyrin vibrations. The vibrational lifetime of the protein amide I band has
663
been measured using single-color infrared transient absorption spectroscopy. The vibrational excitation relaxes rapidly: within 3 ps. The dependence of lifetime on protein structure and on temperature has been measured for three native proteins; myoglobin, azurin and cytochrome c. The tunability of the FBL in combination with its high brightness makes it a nearly ideal source for scanning near-field infrared spectroscopy applications. High resolution infrared images have been obtained on renal tissue sections, using the intrinsic contrast provided by the vibrational absorption bands from identified molecular species within the tissue. The instrument is expected to be used for novel microspectroscopic applications not only in biophysical studies, but also in materials science.
Acknowledgement This work has been supported in part by the Office of Naval Research, Grant No. NOOOl4-94-l-1024.
IX. FEL FACILITY CHALLENGES