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news.usni.org

Report to Congress on Navy Shipboard Lasers - USNI News

The following is from the April. 21, 2022, Congressional Research Service report, Navy Shipboard Lasers: Background and Issues for Congress. From the report This report provides background information and issues for Congress on shipboard solid-state lasers (SSLs) that the Navy is developing for...
news.usni.org news.usni.org
 
bobbymike said:
www.army-technology.com

China's Korla Laser Weapon Satellite: ASAT Site Hacking Western Satellites?

Explore the implications of China's Korla ASAT laser site, potentially disrupting Western satellites with directed energy weapons in BlackSky's intra-day images.
www.army-technology.com www.army-technology.com
Click to expand...
Okay so the enemy laser would have to fool the satellite into thinking it's a legitimate laser communication and tell the satellite to transmit data to an enemy ground-station. But surely the satellite would know where it is and hence that the place it's being told to transmit to is BS?

www.airforce-technology.com

Satellite hack: BAE Systems forecasts major attack within 2023

BAE’s head of space security predicts hack via satellite blinding laser, payload hijacking and insider compromise during 2023.
www.airforce-technology.com www.airforce-technology.com
 
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jsport said:
www.defenseone.com

Why the Navy & Air Force Can't Get Lasers Across the 'Valley of Death'

A new GAO report details missing links in efforts to move directed-energy weapons from the lab to the field.
www.defenseone.com www.defenseone.com
Click to expand...

On the Army, they are actually going to spend a year or so and put a platoon sized DEMSHORAD capability in the hands of soldiers to see if it works as advertised, is operationally effective and can be tactically useful. Once they are reasonably well along in that effort (which started a month or so ago) they will transition the effort to a program of record. The larger 300 kW system will follow the same playbook and the first systems under that effort will be handed over to soldiers next year. Unlike new kinetic systems they cannot avoid this pause between fielding operational prototypes and PoR transition with something as new as Directed Energy. Its much easier to make that transitions on programs like MSHORAD but HEL and HPM efforts need more time with soldiers for both user evaluation and feedback and to work on doctrine, training and tactics.
 
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fredymac said:
HELIOS laser program status and some general comments on HEL weapons.

Lockheed is pursuing fiber based HEL as the winning architecture and they mention 40% efficiency for the Army system. I think slab based HEL is now being left behind and only General Atomics with their HELLADS design will be in contention. For extremely high power, the free electron laser is still the only concept that can get there unless Alkali gas lasers make a surprise showing. With funding finally being restored, the Navy should resurrect the Jefferson Lab 150KW FEL program.

View: https://www.youtube.com/watch?v=HWJY1oB8gSc
Click to expand...
What do you consider to be "extremely high powers?"

In 2022, Lockheed Martin delivered a 300 kW laser weapon to the Army that used spectral beam combining of multiple fiber lasers operating at slightly different wavelengths (see https://optics.org/news/13/9/28 ).

In the 1980s through 1990s, megawatt class continuous wave HF and DF chemical lasers were demonstrated.

In the early 2000s through mid 2010s, megawatt class continuous wave chemical oxygen iodine lasers (COIL) were demonstrated.

All of these lasers have demonstrated continuous wave output powers that far exceed those achieved by any FEL to date.
 
Forest Green said:
Plans for the US GBL were based on a 35MW FEL laser.

Click to expand...
That 35 MW was just a parameter value in the Rand study, which says "FigureA.8 shows the effect for the same target of raising the lasers from the base-case altitude of 1,248 km to 3,367 km (see Table A.2 for a summary of the parameters varied across the various laser case figures).To compensate for the increased range, we have increased the laser’s power to 35 megawatts, but we have cut the number of lasers on orbit in half to twelve."

FEL output power goals being explored for the SDI GBL were from about 10 MW to 100 MW, but these were goals, not demonstrated output power levels.

The highest average power ever from an FEL that I can find in the open literature is 14 kW. See https://en.wikipedia.org/wiki/Free-electron_laser , table 1 at https://www.semanticscholar.org/pap...heng/a417d47b6120e13843e5ef8db06ddff8caac4526 , and https://en.topwar.ru/155723-lazernoe-oruzhie-voenno-morskoj-flot-chast-4.html . The latter link states "Development of the FEL laser for the US Navy is the company Boeing. A prototype of the FEL laser with a power of 14 kW was demonstrated in the 2011 year. At the moment, the state of work on this laser is unknown, it was planned to gradually increase the radiation power up to 1 MW. The main difficulty is to create an electron injector of the required power...The appearance of FEL lasers of sufficient power is difficult to expect in the near future, rather it will happen after the 2030 year."

Note that Boeing was the prime contractor on the SDI GBL program in partnership with Los Alamos National Laboratory. Since Boeing was demonstrating only 14 kW from an FEL in 2011, it is unlikely that they had achieved higher output powers than that from an FEL 20 years earlier under the SDI GBL program.

Certainly, during the SDI era, no FEL had been developed that could be scaled up to 35 MW. The article Fielden, Donald J., "Paper Session III-C - Ground Based Laser System -Defense at the Speed of Light"(1991). The Space Congress® Proceedings. https://commons.erau.edu/space-congress-proceedings/proceedings-1991-28th/april-25-1991/4 from the SDI era in 1991 stated "An RF FEL has not been developed that demonstrates FEL performance that can be scaled to power levels greater than 1 MW."

I'm not saying that FELs can never achieve hundreds of kW to tens of MW average optical power output. I am saying that they are not the only option, and that some chemical, and solid state lasers have demonstrated hundreds of kW average output optical powers, and some chemical lasers have even demonstrated several MW average output optical powers, which far exceed the 14 kW achieved by the highest average optical output power FEL.
 
Table A2 is actually labelled wrongly. Where it says 3.2, it means A7 and everything after is therefore +1. A13 in table should be A14. ;)
 
4MJ is the same energy a 4MW laser puts out over 1s.

Free electron laser system with 4 MJ flash energy for the laser fusion reactor driver

Saldin, E L; Schneidmiller, E A; Ulyanov, Yu N; Yurkov, M V
cds.cern.ch cds.cern.ch
news.fnal.gov

SLAC’s superconducting X-ray laser reaches operating temperature colder than outer space

The facility, LCLS-II, will soon sharpen our view of how nature works on ultrasmall, ultrafast scales, impacting everything from quantum devices to clean energy.
news.fnal.gov news.fnal.gov
 
Forest Green said:
4MJ is the same energy a 4MW laser puts out over 1s.

Free electron laser system with 4 MJ flash energy for the laser fusion reactor driver

Saldin, E L; Schneidmiller, E A; Ulyanov, Yu N; Yurkov, M V
cds.cern.ch cds.cern.ch
news.fnal.gov

SLAC’s superconducting X-ray laser reaches operating temperature colder than outer space

The facility, LCLS-II, will soon sharpen our view of how nature works on ultrasmall, ultrafast scales, impacting everything from quantum devices to clean energy.
news.fnal.gov news.fnal.gov
Click to expand...
That paper by Saldin et. al. presents an analysis of a proposed FEL scheme to achieve up to 4 MJ per pulse. It does not report actually achieving that goal.

Here are some excerpts from that paper showing that it is about a proposed scheme, not actually achieved results: "None of the existing laser systems could provide the required parameters...It was shown in refs. [1-3] that the laser driver for commercial ICF reactor could be constructed on the base of free electron laser (FEL) technique. The scale and cost of the proposed equipment are comparable with the scale and the cost of the equipment for the heavy ion fusion, while the problem of the technical realization seems to be more realistic...In the present paper we propose a novel scheme of a multi-stage FEL amplifier for ICF energy driver...The present design uses four accelerators with relatively low average current...In this paper we also study the problem of matching the output FEL radiation with the optical system of the reactor chamber...An important feature of the proposed driver is that four optical pulses are amplified simultaneously in each FEL amplifier channel... Nevertheless, self-consistent economical analysis shows...Nevertheless, one of the complicated problem to realize the scheme of ref. [1,2] is the requirement on the high value of the average current of the driving RF accelerator...An important feature of the proposed scheme is that it could operate with a larger spacing of electron bunches...Another advantage of the proposed scheme is in providing the absolute contrast of the radiation pulse...When considering possible ways of technical realization of the energy driver, we have used only those technical solution which have been used (or are planned to be used) elsewhere...Using numerical simulation code FS2RN [8] we have optimized parameters of the first stage of the FEL amplifier...The detailed study of the multi-stage FEL amplifier is presented in ref. [1]...Further we assume that the form of the electron beam pulse is a flat one...An important problem is that of extracting the powerful laser beam into the atmosphere. We propose to perform such an extraction at the stage of expansion of radiation...To solve this problem, we propose to use the channel with differential pumping..."

All the other links are also about future capabilities.

One of those links is about a concept design for a future 10 MW electron beam, not a laser.

The others are about x-ray FELs, which are not suitable for long range ground based or shipborne laser weapons because x-rays are highly attenuated by the atmosphere. The x-ray lasers proposed under SDI were for operation in outer space.

The FEL for the SDI ground based laser weapon was designed to operate in the near infrared, originally at 0.8 microns wavelength, but that was eventually changed to 1 micron wavelength for better atmospheric transmission. See https://commons.erau.edu/cgi/viewcontent.cgi?article=3318&context=space-congress-proceedings
 
Forest Green said:
bcredman said:
One of those links is about a concept design for a future 10 MW electron beam, not a laser.
Click to expand...
An electron beam is what drives a FEL though.
Click to expand...
Yes, and an electric current drives a diode laser, and a flash lamp drives some solid state lasers. The driver is just one part of a laser.

Also, note that "For a conventional FEL, the conversion efficiency between the electron beam and optical beam is roughly given by the Pierce parameter, typically on the level of 0.1%." from https://www.sciencedirect.com/science/article/abs/pii/S0168900221009980

The article at that link discussed a proposal for techniques that might improve the efficiency by a factor of about 3, i.e., to 0.3%.

Note that the article does state for FEL amplifiers, which are seeded by another laser, "theoretical studies demonstrate that the maximum conversion efficiency can reach about 50% at X-ray wavelength region when combining a strong undulator tapering with a prebunched beam [10], while at the long wavelength region more than 30% conversion efficiency has been experimentally observed under a strong undulator tapering [20]."

Thus, it is conceivable that a 10 MW electron beam might produce up to a few MW optical power output from an FEL in a master oscillator - power amplifier (MOPA) configuration, but again, this has not yet been demonstrated.

A hybrid fiber laser seeded FEL, is also a possibility, wherein the demonstrated 300 kW output power of a fiber laser might seed an FEL amplifier with a 10 MW electron beam driver to get up to a few MW optical output power. However, would this be better than beam combining more fiber lasers to get to the few MW optical power levels? I don't know since neither have been demonstrated yet.
 
bcredman said:
Yes, and an electric current drives a diode laser, and a flash lamp drives some solid state lasers. The driver is just one part of a laser.

Also, note that "For a conventional FEL, the conversion efficiency between the electron beam and optical beam is roughly given by the Pierce parameter, typically on the level of 0.1%." from https://www.sciencedirect.com/science/article/abs/pii/S0168900221009980

The article at that link discussed a proposal for techniques that might improve the efficiency by a factor of about 3, i.e., to 0.3%.

Note that the article does state for FEL amplifiers, which are seeded by another laser, "theoretical studies demonstrate that the maximum conversion efficiency can reach about 50% at X-ray wavelength region when combining a strong undulator tapering with a prebunched beam [10], while at the long wavelength region more than 30% conversion efficiency has been experimentally observed under a strong undulator tapering [20]."

Thus, it is conceivable that a 10 MW electron beam might produce up to a few MW optical power output from an FEL in a master oscillator - power amplifier (MOPA) configuration, but again, this has not yet been demonstrated.

A hybrid fiber laser seeded FEL, is also a possibility, wherein the demonstrated 300 kW output power of a fiber laser might seed an FEL amplifier with a 10 MW electron beam driver to get up to a few MW optical output power. However, would this be better than beam combining more fiber lasers to get to the few MW optical power levels? I don't know since neither have been demonstrated yet.
Click to expand...
Overall efficiencies of 9.4% have been achieved for FELs.


The transfer from the beam to the seed laser via the Coulomb Effect is far more efficient (see Fig.7).


The seed laser can be relatively low power, since it is the electron beam that adds the power. A reactor can deliver 50MWth (~25MWe) at 10t weight.

www.usnc.com

Nuclear Thermal Propulsion

Nuclear Thermal Propulsion was resuscitated in the 2010s by the efforts at USNC to deliver more capable fuels and designs that use LEU and HALEU rather than military HEU. The work continues.
www.usnc.com www.usnc.com

Scale that up to 40t and you have enough to drive a 9.4MW laser at 9.4% efficiency at a frequency of your choice.
 
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Forest Green said:
bcredman said:
Yes, and an electric current drives a diode laser, and a flash lamp drives some solid state lasers. The driver is just one part of a laser.

Also, note that "For a conventional FEL, the conversion efficiency between the electron beam and optical beam is roughly given by the Pierce parameter, typically on the level of 0.1%." from https://www.sciencedirect.com/science/article/abs/pii/S0168900221009980

The article at that link discussed a proposal for techniques that might improve the efficiency by a factor of about 3, i.e., to 0.3%.

Note that the article does state for FEL amplifiers, which are seeded by another laser, "theoretical studies demonstrate that the maximum conversion efficiency can reach about 50% at X-ray wavelength region when combining a strong undulator tapering with a prebunched beam [10], while at the long wavelength region more than 30% conversion efficiency has been experimentally observed under a strong undulator tapering [20]."

Thus, it is conceivable that a 10 MW electron beam might produce up to a few MW optical power output from an FEL in a master oscillator - power amplifier (MOPA) configuration, but again, this has not yet been demonstrated.

A hybrid fiber laser seeded FEL, is also a possibility, wherein the demonstrated 300 kW output power of a fiber laser might seed an FEL amplifier with a 10 MW electron beam driver to get up to a few MW optical output power. However, would this be better than beam combining more fiber lasers to get to the few MW optical power levels? I don't know since neither have been demonstrated yet.
Click to expand...
Overall efficiencies of 9.4% have been achieved for FELs.


The transfer from the beam to the seed laser via the Coulomb Effect is far more efficient (see Fig.7).


The seed laser can be relatively low power, since it is the electron beam that adds the power. A reactor can deliver 50MWth (~25MWe) at 10t weight.

www.usnc.com

Nuclear Thermal Propulsion

Nuclear Thermal Propulsion was resuscitated in the 2010s by the efforts at USNC to deliver more capable fuels and designs that use LEU and HALEU rather than military HEU. The work continues.
www.usnc.com www.usnc.com

Scale that up to 40t and you have enough to drive a 9.4MW laser at 9.4% efficiency at a frequency of your choice.
Click to expand...
I agree that the seed laser can be relatively low power, but a higher power seed laser may have advantages.

There is a minimum seed power to overcome amplified spontaneous emission, typically at least 9 times the spontaneous power emitted into coherent angle and bandwidth.

The gain depends on the length of the FEL amplifier, so starting with a higher power seed can reduce the length of the FEL amplifier because less gain is needed to produce the required output power.

The paper by Emma et. al. at the link you provided discusses the use of a higher power seed laser for improved efficiency, stating: "Specifically, numerical optimization studies have shown that with a judiciously chosen taper profile, the output efficiency of a seeded FEL can be increased by two orders of magnitude to ∼10% [10,11]. At longer wavelengths, a recent experiment has demonstrated 30% energy extraction from a prebunched electron beam interacting with a large external laser seed in a strongly tapered undulator [16]" (Note that the "longer wavelength" demonstrated in ref [16] is 10.3 microns from a CO2 laser seed with a 200 GW peak power pulse. Ref [16] is at this link: https://arxiv.org/pdf/1605.01448.pdf )

The Emma et. al. paper also states "The results, validated using a fast Matlab-based1D FEL code [17], highlight the importance of an intense input seed power level and of prebunching the initial longitudinal beam distribution."
 
bcredman said:
Interesting article, but since it is about using microwaves to transfer power, why post it to this forum on Solid State Laser News?
Click to expand...
Because it's still sort of beamed energy and there is already a precedent in this thread.
 
Forest Green said:
bcredman said:
Interesting article, but since it is about using microwaves to transfer power, why post it to this forum on Solid State Laser News?
Click to expand...
Because it's still sort of beamed energy and there is already a precedent in this thread.
Click to expand...
Yeah, so is a flash light - still not a laser. ;) Any way, it's not a big deal, and the article is interesting.
 
Forest Green said:
Forest Green said:
Plans for the US GBL were based on a 35MW FEL laser.

Click to expand...
Having read this again, the frequency for their FEL just happens to match an XeF excimer laser precisely.
Click to expand...
The 0.351 micron wavelength also matches that of the tripled Nd:glass laser wavelength used in the Nova laser (which operated from 1984 through 1999) for laser induced fusion experiments. See https://str.llnl.gov/2022-03/koning which states:

"...the decision was made to use 3-omega (0.351-µm wavelength) ultraviolet light for Nova. The 10-beam laser produced up to 30,000 J of ultraviolet laser light and 40 TW of power in 2.5-ns pulses. Nova generated the largest laser fusion yield in prior history—a record 11 trillion fusion neutrons—and achieved implosion symmetry sufficient to compress a fuel capsule to about one-thirtieth its original diameter. During this period, Lawrence Livermore’s broader weapons program and other institutions began using Nova for a wide range of high-energy-density experiments, demonstrating the utility of lasers for understanding issues important to weapon physics."

Note that the National Ignition Facility (NIF) laser induced fusion system also uses tripled Nd:glass lasers at 0.351 microns wavelength. See https://lasers.llnl.gov/about/how-nif-works/final-optics
 
bcredman said:
The 0.351 micron wavelength also matches that of the tripled Nd:glass laser wavelength used in the Nova laser (which operated from 1984 through 1999) for laser induced fusion experiments. See https://str.llnl.gov/2022-03/koning which states:

"...the decision was made to use 3-omega (0.351-µm wavelength) ultraviolet light for Nova. The 10-beam laser produced up to 30,000 J of ultraviolet laser light and 40 TW of power in 2.5-ns pulses. Nova generated the largest laser fusion yield in prior history—a record 11 trillion fusion neutrons—and achieved implosion symmetry sufficient to compress a fuel capsule to about one-thirtieth its original diameter. During this period, Lawrence Livermore’s broader weapons program and other institutions began using Nova for a wide range of high-energy-density experiments, demonstrating the utility of lasers for understanding issues important to weapon physics."

Note that the National Ignition Facility (NIF) laser induced fusion system also uses tripled Nd:glass lasers at 0.351 microns wavelength. See https://lasers.llnl.gov/about/how-nif-works/final-optics
Click to expand...
Yes you can use frequency multiplying materials to triple the frequency of an Nd:Glass laser using phosphate-based glasses, butthe frequency multiplication process isn't 100% efficient, it's 60-80% for doubling, but this involved doubling and mixing, which is likely less efficient. An XeF excimer laser produces 351nm straight from the bat.
 
Forest Green said:
bcredman said:
The 0.351 micron wavelength also matches that of the tripled Nd:glass laser wavelength used in the Nova laser (which operated from 1984 through 1999) for laser induced fusion experiments. See https://str.llnl.gov/2022-03/koning which states:

"...the decision was made to use 3-omega (0.351-µm wavelength) ultraviolet light for Nova. The 10-beam laser produced up to 30,000 J of ultraviolet laser light and 40 TW of power in 2.5-ns pulses. Nova generated the largest laser fusion yield in prior history—a record 11 trillion fusion neutrons—and achieved implosion symmetry sufficient to compress a fuel capsule to about one-thirtieth its original diameter. During this period, Lawrence Livermore’s broader weapons program and other institutions began using Nova for a wide range of high-energy-density experiments, demonstrating the utility of lasers for understanding issues important to weapon physics."

Note that the National Ignition Facility (NIF) laser induced fusion system also uses tripled Nd:glass lasers at 0.351 microns wavelength. See https://lasers.llnl.gov/about/how-nif-works/final-optics
Click to expand...
Yes you can use frequency multiplying materials to triple the frequency of an Nd:Glass laser using phosphate-based glasses, butthe frequency multiplication process isn't 100% efficient, it's 60-80% for doubling, but this involved doubling and mixing, which is likely less efficient. An XeF excimer laser produces 351nm straight from the bat.
Click to expand...

XeF lasers have a typical wall-plug efficiency of only 0.2% which is far lower than the wall-plug efficiency of the NIF tripled Nd:glass laser system which is 0.66% for the flash lamp pumped version and 5% for the diode pumped version as shown in the table below from https://www.osti.gov/servlets/purl/951674 (Note that LIFE is a proposed fusion-fission-hybrid energy generation engine based on laser-driven ICF and the efficiencies in the LIFE column are calculated rather than actually achieved efficiencies as are the values in the two NIF columns):

1686604131887.png
 
bcredman said:
XeF lasers have a typical wall-plug efficiency of only 0.2% which is far lower than the wall-plug efficiency of the NIF tripled Nd:glass laser system which is 0.66% for the flash lamp pumped version and 5% for the diode pumped version as shown in the table below from https://www.osti.gov/servlets/purl/951674 (Note that LIFE is a proposed fusion-fission-hybrid energy generation engine based on laser-driven ICF and the efficiencies in the LIFE column are calculated rather than actually achieved efficiencies as are the values in the two NIF columns):

View attachment 701414
Click to expand...
Odd, I have a book that states efficiencies of up to 15% had been demonstrated with excimer lasers, and it was written in the late '80s.

Now they're stating up to 5% but more with electron beam pumping.

www.rp-photonics.com

excimer lasers

Excimer lasers are lasers where optical amplification occurs in a plasma containing excited dimers with an anti-binding electronic ground state.
www.rp-photonics.com www.rp-photonics.com

Beam pumped.
From 1988

Increased XeF(B→X) laser efficiency at high pump rate and elevated temperature

A XeF(B→X) laser efficiency of 6.0% has been observed in an electron beam pumped device. This is the highest XeF(B→X) laser efficiency reported to date. Mixture
pubs.aip.org pubs.aip.org

Efficient narrowband electron beam pumped KrF laser for pulse‐compression studies

A 25‐J, 50‐ns laser pumped by opposed electron beams is described. Experiments with this device demonstrated a 9% intrinsic laser efficiency at power deposition
pubs.aip.org pubs.aip.org

Direct drive with the argon fluoride laser as a path to high fusion gain with sub-megajoule laser energy - PMC

Argon fluoride (ArF) is currently the shortest wavelength laser that can credibly scale to the energy and power required for high gain inertial fusion. ArF's deep ultraviolet light and capability to provide much wider bandwidth than other ...
www.ncbi.nlm.nih.gov www.ncbi.nlm.nih.gov

LIFE used a solid-state laser known as the Mercury laser, using Yb:SFAP (Ytterbium-doped strontium fluorapatite, Sr5(PO4)3F) as the active gain medium.

Mercury laser - Wikipedia

en.wikipedia.org en.wikipedia.org
 
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bcredman said:
The others are about x-ray FELs, which are not suitable for long range ground based or shipborne laser weapons because x-rays are highly attenuated by the atmosphere. The x-ray lasers proposed under SDI were for operation in outer space.

The FEL for the SDI ground based laser weapon was designed to operate in the near infrared, originally at 0.8 microns wavelength, but that was eventually changed to 1 micron wavelength for better atmospheric transmission. See https://commons.erau.edu/cgi/viewcontent.cgi?article=3318&context=space-congress-proceedings
Click to expand...
A FEL-xaser is going to be an absolutely huge thing, Atomic Rockets says you need most of a kilometer long beam wiggler to generate x-rays.
 
Doesn't really make any sense to use X-ray frequency. Atmosphere would block it. But 1cm is the undulator period for X-rays of 1nm wavelength and about 1000 undulator periods are required, so about 10m. Lower wavelength X-rays would mean shorter periods.
 
Forest Green said:
bcredman said:
XeF lasers have a typical wall-plug efficiency of only 0.2% which is far lower than the wall-plug efficiency of the NIF tripled Nd:glass laser system which is 0.66% for the flash lamp pumped version and 5% for the diode pumped version as shown in the table below from https://www.osti.gov/servlets/purl/951674 (Note that LIFE is a proposed fusion-fission-hybrid energy generation engine based on laser-driven ICF and the efficiencies in the LIFE column are calculated rather than actually achieved efficiencies as are the values in the two NIF columns):

View attachment 701414
Click to expand...
Odd, I have a book that states efficiencies of up to 15% had been demonstrated with excimer lasers, and it was written in the late '80s.

Now they're stating up to 5% but more with electron beam pumping.

www.rp-photonics.com

excimer lasers

Excimer lasers are lasers where optical amplification occurs in a plasma containing excited dimers with an anti-binding electronic ground state.
www.rp-photonics.com www.rp-photonics.com

Beam pumped.
From 1988

Increased XeF(B→X) laser efficiency at high pump rate and elevated temperature

A XeF(B→X) laser efficiency of 6.0% has been observed in an electron beam pumped device. This is the highest XeF(B→X) laser efficiency reported to date. Mixture
pubs.aip.org pubs.aip.org

Efficient narrowband electron beam pumped KrF laser for pulse‐compression studies

A 25‐J, 50‐ns laser pumped by opposed electron beams is described. Experiments with this device demonstrated a 9% intrinsic laser efficiency at power deposition
pubs.aip.org pubs.aip.org

Direct drive with the argon fluoride laser as a path to high fusion gain with sub-megajoule laser energy - PMC

Argon fluoride (ArF) is currently the shortest wavelength laser that can credibly scale to the energy and power required for high gain inertial fusion. ArF's deep ultraviolet light and capability to provide much wider bandwidth than other ...
www.ncbi.nlm.nih.gov www.ncbi.nlm.nih.gov

LIFE used a solid-state laser known as the Mercury laser, using Yb:SFAP (Ytterbium-doped strontium fluorapatite, Sr5(PO4)3F) as the active gain medium.

Mercury laser - Wikipedia

en.wikipedia.org en.wikipedia.org
Click to expand...
I had seen 5% for KrF, but only 0.2% for XeF, so those numbers cover the range in the RP Photonics article. The XeF number was for an electrical discharge pumped XeF laser and came from a very old reference (1976): https://pubs.aip.org/aip/apl/articl...charge-initiated-XeF-laser?redirectedFrom=PDF

Also, some of the larger stated efficiencies may not be wall-plug efficiencies. For example, your link about narrowband electron beam pumped KrF laser for pulse‐compression studies, lists a 9% intrinsic laser efficiency, but that is not a wall-plug efficiency. For electron beam pumped excimer lasers, the intrinsic laser efficiency is defined as the ratio of the laser output energy to the e-beam energy deposited into the laser gas. See https://opg.optica.org/directpdfacc...&id=299350&uri=CLEO-1988-TUO4&seq=0&mobile=no

The link about the ArF laser for direct drive fusion is about ArF, not XeF, and the numbers are projected efficiencies, not achieved efficiencies as indicated in this excerpt "Our laser kinetics simulations indicate that the electron beam-pumped ArF laser can have intrinsic efficiencies of more than 16%, versus about 12% for the next most efficient krypton fluoride excimer laser. We expect at least 10% ‘wall plug' efficiency for delivering ArF light to target should be achievable using solid-state pulsed power and efficient electron beam transport to the laser gas that was demonstrated with the U.S. Naval Research Laboratory's Electra facility."

The 5% wall plug efficiency you stated is on par with the 5% demonstrated by the tripled diode laser pumped Nd:glass laser demonstrated in NIF.

The 15% wall plug efficiency you stated is not significantly different from the 13.3% expected for the LIFE laser, but in both cases these seem to be calculated projections rather than demonstrated wall plug efficiencies.

Consistently throughout my 40-year career in lasers and electro-optics, I saw projected laser efficiencies for new laser technologies that were significantly higher than what was achieved, sometimes by as much as factors of 2 or 3. So, I take the projected efficiencies with a grain of salt.

About LIFE: "LIFE, short for Laser Inertial Fusion Energy, was a fusion energy effort run at Lawrence Livermore National Laboratory between 2008 and 2013...Two designs were considered, operated as either a pure fusion or hybrid fusion-fission system....With the problem of ignition unsolved, the LIFE project was canceled in 2013...The LIFE program was criticized through its development for being based on physics that had not yet been demonstrated. In one pointed assessment, Robert McCrory, director of the Laboratory for Laser Energetics, stated: "In my opinion, the overpromising and overselling of LIFE did a disservice to Lawrence Livermore Laboratory."...LLNL had begun exploring different solutions to the laser problem while the system was first being described. In 1996 they built a small testbed system known as the Mercury laser that replaced the flashtubes with laser diodes." From https://en.wikipedia.org/wiki/Laser_Inertial_Fusion_Energy

The LIFE laser listed in the table I excerpted from the LLNL report was for the hybrid fusion-fission concept, and it's performance listed in the table was a projection, not what was achieved.
 
The 2nd link is broken (no long available on request).

I'm not sure it isn't wall plug efficiency. This suggests it's calculated from the electrical input power:


Using a relatively simple
10-kV power supply to support the discharge implies,
from the electric field requirement noted above, that
the interelectrode spacing will be 10 cm. Making
the beam cross-sectional shape a square produces a
laser cavity as shown in figure 4(a). The electrical
power to produce the laser beam of 1 MW average
power was calculated from the intrinsic efficiency to
be 33 MW.
Click to expand...

Granted, it takes 412MW of solar energy to produce that 33MW, but that's solar panel inefficiency not wall plug.


This makes no mention of 'intrinsic' anyway.

Increased XeF(B→X) laser efficiency at high pump rate and elevated temperature

A XeF(B→X) laser efficiency of 6.0% has been observed in an electron beam pumped device. This is the highest XeF(B→X) laser efficiency reported to date. Mixture
pubs.aip.org pubs.aip.org
 
Last edited:
Forest Green said:
The 2nd link is broken (no long available on request).

I'm not sure it isn't wall plug efficiency. This suggests it's calculated from the electrical input power:


Using a relatively simple
10-kV power supply to support the discharge implies,
from the electric field requirement noted above, that
the interelectrode spacing will be 10 cm. Making
the beam cross-sectional shape a square produces a
laser cavity as shown in figure 4(a). The electrical
power to produce the laser beam of 1 MW average
power was calculated from the intrinsic efficiency to
be 33 MW.
Click to expand...

Granted, it takes 412MW of solar energy to produce that 33MW, but that's solar panel inefficiency not wall plug.


This makes no mention of 'intrinsic' anyway.

Increased XeF(B→X) laser efficiency at high pump rate and elevated temperature

A XeF(B→X) laser efficiency of 6.0% has been observed in an electron beam pumped device. This is the highest XeF(B→X) laser efficiency reported to date. Mixture
pubs.aip.org pubs.aip.org
Click to expand...
I'm confused. The quote you provide says "The electrical power to produce the laser beam of 1 MW average power was calculated from the intrinsic efficiency to be 33 MW." Then you write "This makes no mention of 'intrinsic' anyway." Huh?

Did you mean "This makes no mention of 'intrinsic' anyway." to apply to the last link in your post instead of the previous link?

Anyway, if that is the case, at that last link it states: "A XeF(B→X) laser efficiency of 6.0% has been observed in an electron beam pumped device. This is the highest XeF(B→X) laser efficiency reported to date. Mixtures of NF3 , Xe, and Ne at 425 K and a density of 3 amagat were pumped at a rate of 280 kW/cm3 with a 550 ns pulse. This deposited 150 J/l into the laser gas. Subsequent experiments at 190 J/l input (and 460 K) yielded specific laser outputs as high as 11 J/l."

It does not say explicitly that the "laser efficiency of 6.0%" is the 'intrinsic' efficiency, but note the phrase "This deposited 150 J/l into the laser gas." Now note that it further states "experiments at 190 J/l input (and 460 K) yielded specific laser outputs as high as 11 J/l."

The efficiency of output to input is 11 J/l / 190 J/l = 0.058, i.e., 5.8% which they rounded up to 6%. However, this is an intrinsic efficiency not a wall-plug efficiency since the input is the energy density deposited into the laser gas.
 
Last edited:
bcredman said:
I'm confused. The quote you provide says "The electrical power to produce the laser beam of 1 MW average power was calculated from the intrinsic efficiency to be 33 MW." Then you write "This makes no mention of 'intrinsic' anyway." Huh?


Did you mean "This makes no mention of 'intrinsic' anyway." to apply to the last link in your post instead of the previous link?
Click to expand...
yes. The second comment refers to the 2nd link below it.
bcredman said:
Anyway, if that is the case, at that last link it states: "A XeF(B→X) laser efficiency of 6.0% has been observed in an electron beam pumped device. This is the highest XeF(B→X) laser efficiency reported to date. Mixtures of NF3 , Xe, and Ne at 425 K and a density of 3 amagat were pumped at a rate of 280 kW/cm3 with a 550 ns pulse. This deposited 150 J/l into the laser gas. Subsequent experiments at 190 J/l input (and 460 K) yielded specific laser outputs as high as 11 J/l."

It does not say explicitly that the "laser efficiency of 6.0%" is the 'intrinsic' efficiency, but note the phrase "This deposited 150 J/l into the laser gas." Now note that it further states "experiments at 190 J/l input (and 460 K) yielded specific laser outputs as high as 11 J/l."

The efficiency of output to input is 11 J/l / 190 J/l = 0.058, i.e., 5.8% which they rounded up to 6%. However, this is an intrinsic efficiency not a wall-plug efficiency since the input is the energy density deposited into the laser gas.
Click to expand...
Quite possibly.

It look like fibre lasers are going to be the way forward based on current efficiencies.
 
Forest Green said:
bcredman said:
I'm confused. The quote you provide says "The electrical power to produce the laser beam of 1 MW average power was calculated from the intrinsic efficiency to be 33 MW." Then you write "This makes no mention of 'intrinsic' anyway." Huh?


Did you mean "This makes no mention of 'intrinsic' anyway." to apply to the last link in your post instead of the previous link?
Click to expand...
yes. The second comment refers to the 2nd link below it.
bcredman said:
Anyway, if that is the case, at that last link it states: "A XeF(B→X) laser efficiency of 6.0% has been observed in an electron beam pumped device. This is the highest XeF(B→X) laser efficiency reported to date. Mixtures of NF3 , Xe, and Ne at 425 K and a density of 3 amagat were pumped at a rate of 280 kW/cm3 with a 550 ns pulse. This deposited 150 J/l into the laser gas. Subsequent experiments at 190 J/l input (and 460 K) yielded specific laser outputs as high as 11 J/l."

It does not say explicitly that the "laser efficiency of 6.0%" is the 'intrinsic' efficiency, but note the phrase "This deposited 150 J/l into the laser gas." Now note that it further states "experiments at 190 J/l input (and 460 K) yielded specific laser outputs as high as 11 J/l."

The efficiency of output to input is 11 J/l / 190 J/l = 0.058, i.e., 5.8% which they rounded up to 6%. However, this is an intrinsic efficiency not a wall-plug efficiency since the input is the energy density deposited into the laser gas.
Click to expand...
Quite possibly.

It look like fibre lasers are going to be the way forward based on current efficiencies.
Click to expand...
I agree that fiber lasers will be the way forward, at least for the foreseeable future.

In addition to their high efficiencies, they are easier to make relatively compact and robust for fielding than most other laser types, and it is fairly straightforward at this point to scale up output power while maintaining brightness by either spectral or phased beam combining.

They can probably scale up to the MW class output power, but who knows if they will be able to scale beyond that to the tens of MW to hundreds of MW class that may be needed for ground-based long range ballistic missile defense applications. For that we may need a big FEL or chemical laser or excimer laser or gas laser or perhaps some new type of laser that has not been invented yet.

Alternatively, rather than scaling to extremely high average powers, there seem to be early indications that very high peak power ultrafast/ultrashort pulse lasers may have potential for weapons applications in the future. See https://breakingdefense.com/2021/10/rapid-pulse-laser-weapons-could-be-the-pentagons-future-edge/ and https://idstch.com/technology/photo...emtosecond-laser-directed-energy-weapons-dew/ and https://www.nre.navy.mil/organizati...weapons-uspl-and-atmospheric-characterization
 

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