UNCLASSIFIED

UNCLASSIFIED

EXPERIMENTAL METHODS FOR

MULTI-GENRE NETWORKS

BackgroundApplications for Mid-IR Lasers

• As we can see the transmission percentage is high between 3-5 (mid-IR) microns and 8-

14 microns (IR) for wavelengths of radiation

Lasers operating in the 3-5 and 8-12 μm wavelength ranges can make use of high atmospheric transmission for

long distance applications. Because of the long wavelengths these lasers are much less sensitive to bad weather

and smoky conditions.

• Remote sensing of atmospheric gases & biochemical agents

(e.g. environmental monitoring, atmospheric pollution control)

• Free space communications

More data can be transmitted in the region of 3-5 and 8-14 microns.

The research goal is to develop mid-infrared laser sources from rare-earth doped low-phonon

crystalline materials that can be efficiently pumped by diode lasers. These lasers have a

variety of uses whether in communications, sensing biochemical agents, and even in medical

fields. When developing rare-earth doped laser materials, one of the main considerations is

storage lifetime for the upper laser level. It is advantageous for the emission lifetime to be as

long as possible, so that the population inversion can be maximized. In rare-earth doped

systems, radiative lifetimes are not easy to measure because it is hard to separate out

nonradiative processes. There are several methods to predict radiative lifetimes; the most

popular being Judd-Ofelt theory, which has been used for over 50 years for the analysis of

spectroscopic properties of rare-earth ions. Alternatively, another method called Reciprocity

of absorption and emission (the cross section comparison method) provides a way to cross

check the values determined from the Judd-Ofelt theory. In this work, MathCAD was

employed to solve for the Judd-Ofelt parameters while Originlab was used to calculate the

Reciprocity method. Then we compared the two results to find reasonable agreement in order

to know whether the rare-earth doped gain materials are suitable for use in the mid-infrared

laser applications.

MethodsA. Judd-Ofelt (J-O) Theory:

B. The Cross-Section Comparison Method:

Reciprocity & Füchtbauer-Ladenburg (F-L)

j

ZLj

ju

i

iil

ZL

u

labsorptionemission

kT

EEd

Z

kT

EdZ

kThc

EZ

Z

))(

exp(

)exp(

]/)exp[()(

dI

I

cn rad

emiss)(

)(

8

1)(

5

2

Measure Integrated Absorption Coefficient

Determine measured Sed

line strength

Using matrices from literature to solve for the Ω values.

Calculate Transition probabilities

Results in Radiative Lifetimes and

Branching Ratios

1850 1900 1950 2000 2050 2100 2150

0

0.5

1

1850 1900 1950 2000 2050 2100 2150

0

0.5

1

1850 1900 1950 2000 2050 2100 2150

0

0.5

1

Wavelength (nm)

Emission spectrum

rad = 10.75 ms

Cro

ss-S

ecti

on

(x10

-20cm

2)

Reciprocity

EZL = 5100.7 cm-1

Zl/Zu = 0.909

RT

absorption spectrum

Fluorescence Spectroscopy and Judd-Ofelt Calculations for Rare-Earth doped Crystals

Results & Discussion

Student: Cameron Moneypenny, cameron.moneypenny@gmail.com

Mentors: Ei Ei Brown, eiei.brown.civ@mail.mil

Abstract

Solid-State Lasers Compact and rugged

Can work at room and cryogenic temperatures

Pulsed or continuous modes

Low beam divergence

High pump efficiency

Research Objective

• Study absorption and emissionspectroscopy of RE doped Crystals

• Study Judd-Ofelt theory & Reciprocityof absorption and emission to predictradiative lifetimes and branching ratios

• Compare the two results to findreasonable agreement between the twomethods for Holmium doped K2LaCl5

,)(

)2(

9

8

)12(3)(

2223

d

n

n

Ne

JhcJJS

RE

ed

meas

2( )

2,4,6

( ) ( , ) ( , ) ,ed t

calc t

t

S J J S L J U S L J

4 2 2 23

3

64 ( 2)( ) ( ) ( ) ,

3 (2 1) 9

ed md

calc calc

e n nA J J S J J n S J J

h J

( )( )

( )t

A J JJ

A J

1

( )rad

tA J

F-L method requires accurate knowledge

of emission spectrum, radiative lifetime &

branching ratio.

Rec. method requires accurate

knowledge of Stark levels and

dopant concentration

• Judd-Ofelt theory allows the calculation of rare-earth transition strengths and radiative lifetimes from

measured absorption spectra.

• Eight absorption bands selected for evaluation of the t parameters, known as the J-O intensity

parameters.

• The intensities of the transitions can be distinguished by their line strength, S, for of each SLJ state.

References1. B. Walsh, “Judd-Ofelt Theory: Principles and Practices”, B. Di Bartolo and O. Forte (eds.),

Advances in Spectroscopy for Lasers and Sensing, 403-433. 2006 Springer, Netherlands.

2. B. Walsh, N.P. Barnes, B.D. Bartolo, J. Appl. Phys. 83 (1998) 2772-2787.

3. M. Eichhorn, Appl. Phys. B 93 (2008) 269-316.

• The percent difference between the two methods is ~17.3 % with the Judd-Ofelt

calculations having a 13.0 ms & 10.75 ms radiative lifetime for Reciprocity method,

which showed reasonable agreement for the two theories on the radiative lifetime of

Ho3+ doped in K2LaCl5.

• It was known that Judd-Ofelt theory and cross-section comparison method have

errors of 15-20 % for the prediction of radiative lifetimes.

• Further work could be performed by comparing these radiative lifetimes with the

fluorescence lifetimes measured at low temperature at 10-20 K.

Conclusions & Path Forward

Known Parameters

∫ () d: Integrated absorption coefficient for each band

: Tabulated in tables (e.g. Kaminskii)

Unknown Parameters

t : Intensity parameters, t = 2,4,6

Radiative transition probabilities: Radiative lifetime: Branching ratio:

Integrated absorption coefficients,

experimental and calculated line

strengths of Ho:K2LaCl5

Transitions (from 5I8)

Average Wavelength (nm)

α(λ)𝒅λ

(nm/cm)

Smd

(x10-20 cm2)Smeas

(x10-20 cm2)(experimental)

Scalc

(x10-20 cm2)(calculated)

5I7 1999.4 21.8149 0.952 3.712 2.9485I6 1173.5 3.5139 1.306 1.1945I5 901.3 0.4015 1.943 1.8065F5 649.4 4.56 3.062 3.1535S2+5F4 541.4 3.499 2.819 2.5985F3 486.7 0.5829 5.223 4.6513K8 471.6 0.7998 7.396 5.2675G6+5F1 455.1 14.8226 1.42 1.42

Transitions Aij (s-1) ij

(BranchingRatio) %

rad

(ms)

5I7 5I8 79.087 100 13.0

5I65I7 20.846 11.2

5I65I8 165.105 88.8 5.38

5I55I6 8.689 5.7

5I55I7 78.433 51.8

5I55I8 64.306 42.5 6.60

Absorption Spectrum Overview Fluorescence Spectra

MathCAD

Originlab

• Absorption cross section was

exploited to obtain the emission

cross-section using the

reciprocity.

• Radiative lifetime was “derived”

from matching the peak emission

cross sections for the F-L relation

& the Reciprocity method.

abs = /Nconc

Calculated radiative transition probabilities (Aij), branching

ratios (ij), and calculated radiative lifetimes (rad)

Valuable skills and beneficial experience gained from this summer research

program:

1. proficiency in the use of software tools such as Mathcad and Originlab

2. skills and knowledge gained on rare earth spectroscopy research under

the supervision of my mentor, Dr. Ei Ei Brown.